Home Energy Diet

THIS CHAPTER INTRODUCES A NUMBER OF IMPORTANT CONCEPTS and definitions regarding energy use. How much energy do we use? Where does it come from? Where does it go? Why does it matter? Where does one start thinking about energy? By the time you are finished reading this chapter, you will be able to grasp global and local energy issues and speak intelligently to your contractors about which fuels you might want to use in your home.

Our homes generally consume one or more primary fuels in addition to electricity. A primary fuel is one that can be used in a relatively unprocessed form to deliver the energy required for any number of different uses. Examples of primary fuels include oil, coal, uranium, wood, natural gas, propane, water, wind, and solar power.

The most common primary fuels used in homes are natural gas (NG), liquid propane gas (LPG), and oil. Kerosene and coal are also used, though infrequently. Those in more rural regions may add wood to this list. Most homes take advantage of the ultimate primary energy source, the Sun, to some degree, if proper design is considered before construction.

Electricity can be considered asecondary power source as it is not really a fuel, but an energy carrier, bringing to your home the energy embodied in the primary fuels from which it was produced.

We all use fossil fuels; entire societies have been built on their use throughout the past 150 years. We know that they work reliably to bring us warmth and power, and that they’re relatively inexpensive, but we now also know that their use has a high environmental cost. All fossil fuels contain the elements carbon and hydrogen. Thus, they are known as hydrocarbons. The vast portion of energy available in a fuel comes from its hydrogen content, whereas the carbon generates much of the waste, resulting in pollution. Gasoline, heating oil, and propane are over 80 percent carbon by weight. Natural gas contains 75 percent carbon by weight; the remainder is hydrogen.

Pure hydrogen gas (H₂) is the cleanest energy source and the most abundant element in the universe. Burning pure hydrogen for energy creates only water vapor as a byproduct. Hydrogen fuel cells have received lots of attention lately because they are potentially a very clean source of energy. However it is the source of the hydrogen that is at issue. Hydrogen is difficult to find on its own in nature, and needs to be liberated from the substance in which it is found. Most of the hydrogen on the earth is bound up in water (H₂O), and separating water into its constituent hydrogen and oxygen is an energy-intensive process. Fuel cells in use today typically rely on hydrogen-rich fossil fuels for the source of hydrogen.

What we commonly call combustion, or burning, is chemically known as oxidation: a reaction between the fuel and oxygen in the air. Both useful heat energy and wasted byproducts — or pollution — are liberated from fuels by oxidation. Combining hydrogen in the fuel with oxygen in the air releases energy, but when oxygen in the air combines with carbon and sulfur in the fuel and nitrogen in the air during the combustion process, the result is air pollution. These pollutants include carbon dioxide (CO₂), carbon monoxide (CO), nitrogen oxides (NOX), sulfur oxides (SOX) and particulates.

Before we get too far into a discussion of energy, it would be useful to know how to quantify it.

We buy energy in units. The specific unit depends on the type of fuel. Liquid fuels such as oil, gasoline, and liquid petroleum gas (LPG) are sold in gallons, natural gas is sold by the therm or by the cubic foot, and electricity is measured and sold in kilowatt-hours.

When comparing fuels and their energy content, we need to find a common denominator for all energy measurement units regardless of fuel. We need to compare apples to apples. The energy “apple” (at least in the US and Britain) is the British Thermal Unit, or Btu. By definition, a Btu is the amount of energy required to raise the temperature of one pound of water (about a pint) by 1°F.

For perspective, one Btu is approximately the amount of energy released by completely burning a wooden kitchen match, and there are about 5.8 million Btus in a 42-gallon barrel of oil. Oil is bought and sold on the global market in units called barrels.

A Btu is a fairly small unit of energy. It may take 50 to 100 million Btus or more to heat and/or cool a home over the course of a year. How much energy you use depends on your climate, your home’s efficiency, and how you operate your heating and cooling equipment. When large quantities of energy are compared — such as how many Btus are required to heat a home, or when comparing fuel costs — it is common to think in terms of million Btus, or MMBtu. One million Btus is the amount of energy contained in a little over seven gallons of oil.

Calorie counters may find this relationship helpful: a gallon of gasoline contains the equivalent of about 31,000 food calories (kilo-calories). This is equivalent to the energy in over 50 McDonald’s Big Macs!

On a global scale, energy is measured in quads, or quadrillion Btus. (One quadrillion is 1 followed by 15 zeros.) There are 172.4 million barrels of oil in a quad. All the energy consumed in the United States amounts to just under 100 quads of energy each year, about one quarter of the world’s total energy consumption.

Measuring electrical energy is a little different. While we can still speak in terms of Btus when talking about electricity, the more common units are the watt and the watt-hour. Electric power usage is measured in watts. We use the term “watts” all the time when we buy light bulbs. How many watts an appliance uses represents its energy demand. Some larger electrical measuring units to know are:

When we leave the lights on, power is consumed over time. The way to measure electrical power consumed over time is with the watt-hour or more commonly, the kilowatt-hour, or kWh. Electric companies bill us in kilowatt-hours.

For example, a 100-watt light bulb consumes 100 watt-hours when left on for one hour. After ten hours, the same bulb has consumed 1,000 watt-hours, or one kWh. A ten-watt night-light needs to be on for 100 hours to add up to one kWh of power. One kilowatt-hour represents an energy content of 3,413 Btus. An average home might use between 300 and 1,000 kilowatt-hours each month. When speaking of larger electrical production or consumption such as what a power plant produces, we’ll need some convenient terms to represent these larger numbers:

A kWh is the consumption of 1,000 watts over aperiod of one hour, or any product of time and electrical power demand that adds up to 1,000 watt-hours.

A number of energy sources fuel our lives. We’ll take a closer look at each one to discover where each fuel comes from and how it is used. To put things in context, we’ll start with a look at the big picture of global and US energy consumption, then examine how energy is used, where it comes from, and where it goes. The remaining chapters will narrow the focus to the energy used in your home.

The annual energy consumption figures used throughout this chapter are based on the most recently available data from the US Energy Information Administration. The years range between 2000 and 2002, which may at first appear confusing, but during that time span the percentages and consumption data changed very little.

In 2002, the world used 409 quads of energy. Figure 1.1 shows the sources of energy used by the world.

With the world’s largest economy, the United States is also the world’s biggest producer and consumer of energy. In 1950, the US was energy independent, consuming under 35 quads of energy. Fifty years later, our population had increased by 189 percent while energy use grew by 280 percent.

One positive spin on US energy consumption is that we are getting more efficient in terms of energy used for each dollar of Gross Domestic Product (GDP), a concept known as energy intensity. In 1950, we consumed just over 20,000 Btus for every dollar of GDP. By 2001, that figure declined to just under 10,000 Btus per dollar of GDP and continues to drop. However, one could easily argue that this decrease in energy consumption is tied to the loss of manufacturing facilities, as we become a nation of less energy-intensive service and information providers.

In 2002 the US consumed 97.3 quads of energy — about 24 percent of the world’s total annual energy use, equivalent to the energy contained in nearly 17 trillion barrels of oil. This figure is expected to rise to 131 quads by 2020.

Americans burned up an average of 339 million Btus each in 2002, or the equivalent of about 2,450 gallons of oil. In terms of air pollution, the average American’s annual energy-consumption habits produce about 22 tons of the potent greenhouse gas, carbon dioxide (CO₂), a major factor in global warming. In terms of dollars, US consumers spent about $703 billion on energy in 2000, representing about 7.2 percent of the $9.8 trillion GDP for that year.

Some of these primary sources are used in the generation of secondary sources such as gasoline (refined from oil) and electricity (derived from any of these primary sources). Figure 1.3 is a flowchart showing energy flows — inputs, uses, and outputs — in the US in 2002. The chart may at first appear confusing, but if there is one point I want you to grasp here it’s that over half the energy we produce is wasted! You’ll learn where the majority of this waste comes from in Chapter 2.

In 2002, US net fossil fuel energy imports totaled 25.4 quads, about 26 percent of total energy consumption, valued at $105 billion. Nearly 60 percent of petroleum products were imported, along with 16 percent of the natural gas we consumed. We imported 81 percent of the uranium used in nuclear reactors,

Fig. 1.3: US energy inputs by fuel and outputs by sector, 2002. Credit: University of California, Lawrence Livermore National Laboratory, and US Department of Energy.

bringing the total net fuel energy imports up to about 33 percent. Coal is the only primary fuel the US has an abundance of and does not need to import. Energy imports (including enriched uranium) accounted for 24 percent of 2002’s $483 billion trade deficit.

Table 1.1 shows energy consumption in several countries compared with population and gross domestic product in 2002. The 37 countries represented consumed 67 percent of the world’s energy. Take a look at one of those photos of the earth at night from space — you can tell who the wealthy countries are because they leave the lights on! You can find one of these photos on the web at <http://antwrp.gsfc.nasa.government/apod/image/0011/earthlights_dmsp_big.jpg>.

Western Europe includes: Austria, Belgium, Bosnia and Herzegovina, Croatia, Denmark, Farce Islands, Finland, France, Germany, Gibraltar , Greece, Iceland, Ireland, Italy, Luxembourg,

Macedonia, TFRY, Maki, Netherlands, Norway, Portugal, Serbia and Montenegro, Slovenia, Spain, Sweden, Switzerland, Turkey, United Kingdom.

Note the high use of energy in the US as compared with population.Associated with this high rate of energy use are a high level of electrification, the world's highest GDP, and extensive land area.

Now that we know what the global and national energy pies look like, let’s take a closer look at each slice to learn something about the fuels used to energize our society.

Coal is a combustible black or brownish-black rock, formed from plant remains that have been compacted, hardened, chemically altered, and metamorphosed by heat and pressure over geologic time. Standard classifications of coal include (from soft to hard) lignite, sub-bituminous, bituminous, and anthracite. These ranks are based on carbon content, volatile matter, heating value, and agglomerating (caking) properties.

Due to its fairly low cost and domestic abundance, coal remains a very popular industrial fuel. The US imported only about four percent of the coal it used in 2000. About 90 percent of the coal consumed in the US is used to produce over 50 percent of our nation’s electricity. On average, a ton of coal contains about 21 million Btus, the equivalent of about 150 gallons of oil. The nation consumed over one billion tons of coal in 2000, representing about a quarter of US energy consumption.

The first nuclear plant in the US was built in Shippingport, Pennsylvania, in 1957. The last order to build a new nuclear plant came in 1977, two years before the Three Mile Island accident. In 2000, 103 nuclear reactors within 66 US nuclear power plants (there are 442 in the world), generated about 20 percent of our nation’s electricity. In 2000, 51.5 million pounds of uranium were loaded into nuclear reactors. Seventy-seven percent of this uranium was imported. Our primary foreign sources of uranium are Canada, Russia, Australia, and Uzbekistan.

One pound of enriched uranium contains about 33 billion Btus of energy, the equivalent of approximately 240,000 gallons of oil, 1,500 tons of coal, or 10 megawatt-hours of electricity — enough to power 1,000 homes for a year. However, only about four percent of the fissionable material available in a pound of uranium is used up in a nuclear reactor, and reactors operate at an efficiency of about 31 percent. Adjusting for these factors, the amount of energy converted from a pound of enriched uranium by a nuclear power plant is equivalent to approximately 3,300 gallons of oil, 23 tons of coal, or 134,000 kilowatt-hours of electricity — enough to power about 14 homes for a year.

Nuclear power plants are clean in actual operation, and the fuel is relatively inexpensive (around $11 per pound for wholesale uranium). However, uranium strip mines do terrible environmental and social damage, and there is still no place to put the radioactive waste generated by nuclear reactors. The US Department of Energy’s Energy Information Administration (EIA) reports: “A 1982 law required the Department of Energy to dispose of spent fuel as of January 31, 1998; however, feasibility studies have yet to be completed for an underground site in Nevada’s Yucca Mountain, located 100 miles north of Las Vegas. Meanwhile, utilities are complaining that they are running out of nuclear waste storage capacity at their nuclear plants.”

It is likely that the Yucca Mountain site will eventually accept nuclear waste, but the US General Accounting Office reports that the site will not be ready until 2015. In addition, there are some very real safety concerns associated with the many truck and train trips required to move radioactive waste around the country. There are over 40,000 tons of radioactive waste from US nuclear power plants awaiting permanent storage. This waste is accumulating at a rate of nearly 2,000 tons per year. The Yucca Mountain site has an uncertain capacity, but the assumption is that it will hold about 70,000 tons of waste. At current waste production rates, the facility will be full in fifteen years — by the time the site opens, a new one will be required!

Hydro power represents over 40 percent of our renewable energy consumption, contributing about 2.4 percent (2.3 quads) to the nation’s total energy use in 2001.

Actual hydro power contribution to the national electric grid varies between 7 and 12 percent depending on rainfall and water levels.

Hydro power plants convert the energy in flowing water into electricity by using a dam on a river to retain a large reservoir of water. Water can be released under controlled conditions and used for mechanical power, or sent through turbines to generate electrical power. American Rivers, a non-profit conservation organization, notes that there are 75,000 dams greater than six feet in height in the United States, and less than three percent are used to generate electricity. The remainder are used for flood control, municipal and agricultural water supply, or are leftover and unused from mill operations of the past.

One of the drawbacks to hydro power is that some of the projects are so large that many thousands of people, plants, and animals have been displaced from their flooded homes. Hydro-Quebec in Canada (delivering power to the northeastern US and Canada), operates 51 separate hydroelectric generating stations with a capacity of over 30,000 megawatts from 561 dams and 24 large reservoirs. One of these projects, the La Grande dam, flooded 3,822 square miles of land inhabited by the native Cree people. The Three Gorges project on the Yangtze River in China will be the world’s largest hydroelectric dam, stretching over 1.4 miles with a generating capacity of over 18 gigawatts. Scheduled for completion in 2009, Three Gorges will create a 375-mile long reservoir, and displace about 1.5 million people.

Natural gas (NG) is a gaseous mixture of hydrocarbon compounds, primarily methane, found along with oil deposits or on its own. Methane can also be captured from landfills as organic materials decompose, and from animal wastes by a process called anaerobic digestion — a breakdown of organic material in the absence of oxygen. Natural gas is somewhat cleaner burning and more versatile than heating oil, and can be used in homes for space and water heating, as well as for cooking and clothes drying. Due to the cost of underground or overland pipelines, and because it is difficult to transport by truck or rail, availability of natural gas is limited to higher population centers where the over 1.1 million miles of pipelines can transport it from 400 thousand wells to power plants, industry, and homes.

Natural gas can also be used to fuel vehicles in slightly modified gasoline burning engines. The gas is stored on board the vehicle in tanks as compressed natural gas (CNG), or cooled to an even more energy-dense liquid state called liquefied natural gas (LNG). The volume of the liquid natural gas is 1/600th that of the gas in its vapor state, increasing its energy density. Unfortunately, it takes quite a lot of energy to compress natural gas, along with specialized handling equipment. This limits our ability to import natural gas from abroad.

Natural gas has received a fair amount of attention lately as a clean-burning fuel that may allow us to transition from fossil fuels altogether. Like all other fossil fuels, there is a finite supply of natural gas, and “clean” is only a relative term. However, because of this clean reputation, the majority of future power plants will likely be fueled by natural gas.

Natural gas has an energy content of approximately 1,000 Btus per cubic foot, depending on the level of purity. It is usually measured and sold in cubic feet (cf), hundreds of cubic feet (Ccf), or units called therms. A therm is equivalent to 100,000 Btus, or approximately 100 cubic feet. Homeowners throughout the country pay an average $1.00 per therm to purchase natural gas; the price has been extremely volatile in recent years.

According to the EIA, the US has proven natural gas reserves of 177 trillion cubic feet (Tcf) (about three percent of world reserves), and currently consumes natural gas at a rate of nearly 23 Tcf per year, representing about a quarter of

US energy consumption. In 2000, 15 percent of natural gas was imported; over 99 percent of this came from Canada via pipeline.

Liquefied petroleum gas (LPG) is a petroleum distillate sometimes known as “bottled” gas, and is similar to natural gas. LPG consists of a group of hydrogen-rich gases — propane, butane, ethane, ethylene, propylene, butylene, isobutane, and isobutylene — derived from the process of refining crude oil or natural gas. For convenience of transportation, these gases are liquefied through pressurization. LPG has an energy content of about 91,690 Btus per gallon, or 2,516 Btus per cubic foot. Many people know LPG as the fuel used for the backyard grill.

LPG is commonly used in rural areas where no natural gas pipeline exists, and can be used with natural gas equipment with only minor adjustments. LPG is delivered by truck to where it is needed and dispensed into storage tanks or bottles.

Over 6.5 billion gallons of LPG were used in homes in 2000; 71 percent was used for space heat, 22 percent for hot water, and 7 percent for appliances such as stoves and refrigerators. The price of propane fluctuates wildly depending upon how much of it you use, and if you buy it in bulk (pre-buy for the season)

or on the spot market (will-call, as needed). You can expect to pay between $1. 50 and $3 per gallon to use propane in your home.

Home heating oils include #2 fuel oil, kerosene (#1 fuel oil), and sometimes diesel motor fuel. Equipment designed for one of these fuels can usually operate acceptably with all of the others. The main difference is the purpose for which they are sold. Home heating oil is nearly identical to diesel motor fuel, but the diesel fuel may have additives to prevent gelling in cold weather. In cold climates, it is necessary to have an indoor space to store home heating oil so that it doesn’t thicken, or gel, in cold temperatures. If cold is a problem, kerosene can be mixed with the heating oil to lower the gelling temperature. In addition to having a lower gel temperature, kerosene is slightly lighter in weight and slightly lower in energy content than home heating oil.

Fuel oils have an energy content of approximately 135,000 to 140,000 Btus per gallon, and are generally low-cost fuels due to their high energy density. The price fluctuates, but averages about $1.50 per gallon. Diesel motor fuel is taxed by federal and state government highway departments and is typically a bit more expensive than kerosene and home heating oil. Due to the highway tax imposed on motor fuels, it is illegal to use untaxed kerosene in place of diesel

motor fuel. Red dye is used in kerosene for the purpose of identification for consumers and law enforcement agents.

About 6.1 billion gallons of fuel oil and kerosene were used in our homes in 2000, 84 percent for space heat, the remainder for hot water heating. Over 80 percent of this oil was used in New England and the mid-Atlantic states.

Wood is a non-fossil, renewable hydrocarbon fuel. While wood fires can be smoky, releasing high quantities of particulate matter, the Environmental Protection Agency has set efficiency guidelines for wood-burning equipment. Wood is burned in an airtight wood stove, allowing for a controlled burn based on how much air is allowed into the combustion chamber. When modern wood-burning appliances are used, wood is generally a more environmentally friendly energy source than fossil fuel. Trees take up carbon dioxide from the atmosphere while they are growing and release it when oxidized in a fire. Thus, there is no net carbon dioxide (CO₂) gain in the atmosphere. If left to decay on the forest floor, wood eventually releases the same amount of CO₂ as when burned, albeit over a much longer period of time. Wood is most commonly used in rural areas as a primary or backup fuel for space heating and sometimes for hot water.

The energy content of wood varies by species, but a full cord (a stack measuring 4 feet × 4 feet × 8 feet) of mixed hardwood weighs about two tons and contains about 20 million Btus — the equivalent energy of 145 gallons of fuel oil, or about a ton of coal. Harder woods (such as oak, beech, and maple) have higher energy content than softer woods (pine, hemlock, and aspen). Wood availability and prices vary greatly throughout the country, but the cost per unit of energy is generally about the same as heating oil. A cord of wood costs in the neighborhood of $150, depending on when you buy it, what part of the country you live in, and whether you buy it green or seasoned.

Each day more solar energy falls to the Earth than the total amount of energy the planet’s six billion inhabitants would consume in 27 years. The desert region of the southwestern United States receives almost twice the sunlight as other regions in the US, making it one of the world’s best areas for solar energy. Globally, other areas with high solar intensities include developing nations in Asia, Africa, and Latin America. These countries need education and incentives to foster a sustainable energy future rather than buying into the dirty fossil fuel-based energy we’ve exploited during the twentieth century.

If you have a suitable house site, solar and/or wind energy can be used to heat your house and your water, or generate electricity; and regardless of where you are on the planet, renewable energy can meet some or all of your energy needs. Many states and utilities offer financial incentives for the purchase and use of renewable energy. These incentives can be in the form of tax credits or cost sharing, and are in a constant state of flux due to budget and other concerns. To see what renewable energy incentives your state offers, visit the website of the Database of State Incentives for Renewable Energy (DSIRE), a comprehensive source of information on state, local, utility, and selected federal incentives that promote renewable energy, at <www.dsireusa.org>

In addition to the sun and wind, efforts are being made to harness thermal and electrical energy from the oceans, biomass — including wood, biodiesel (a vegetable-oil-based diesel fuel substitute), ethanol (an alcohol-based gasoline substitute) — and hydrogen, which can be used in any number of transportation and home energy situations.

Local streams can be employed to generate hydroelectric power in quantities that are suitable for an efficient home. Many rural homes use these micro-hydro systems without altering the stream and often without the need for permits. Specific information about solar, wind, and other renewable energy systems for your home can be found in an excellent magazine called Home Power, on the web at <www.homepower.org>.

Deep down at the core of the earth, temperatures reach about 7,600°F. It is estimated that 42 trillion watts of energy is continuously radiated from the earth into space. That adds up to 3.4 quads of energy every day, about three times the daily energy consumption of all humanity.

Geothermal energy can be used on a large scale to generate electricity, or at home to help heat your living space or hot water.

There are a few places on the planet where the intense heat from magma or steam from geysers is close enough to the surface (.5 to 2.5 miles deep) to be used cost-effectively to provide high pressure steam to drive utility-scale electric generators, or to capture the heat for buildings or industrial processes. More practical for home energy use is the top 20 feet or so of the earth’s crust where a constant temperature of between 50 and 60°F is maintained depending on climate and depth. It is possible to use this fact to our benefit in transferring heat from the ground to water or air. Geothermal heat can be obtained from the ground or from water in lakes or drilled wells. Because moving heat requires less energy than creating it, geothermal heat pumps can save on home energy costs by delivering more energy than they consume. For more information on geothermal energy, look into the Geothermal Energy Association on the web at <www.geo-energy.org>.

Now that we’ve reviewed energy supply, let’s look at the demand for energy. There are four large categories, or sectors, of energy consumption:

Remember that energy doesn’t just go away after we use it. The inherent energy of a fuel is not consumed, but transformed into work, heat, and waste. Every gallon of gasoline you burn in your car’s engine produces mechanical energy, heat, and nearly twenty pounds of CO₂, along with other gases such as oxides of sulfur and nitrogen.

Of the fuels used as primary energy sources, nuclear, hydro, wind, and solar power are all used to generate electricity. That leaves us with three giant slices of the energy pie to look more closely at. These are oil, natural gas, and coal. Let’s make a pie out of each of these to see what each fuel is used for. Figures 1. 5 through 1.7 show the end uses of each of these fuels.

Of the nearly 20 million barrels (840,000,000 gallons) of oil Americans use every day, about 43 percent (361,200,000 gallons) goes straight into our gas tanks; the remaining portion of that shown for “transportation” is primarily diesel, jet fuel, and lubricants. Petroleum refining is the most energy-intensive manufacturing industry in the United States, accounting for about 7.5 percent of total US energy consumption, while supplying about 40 percent of America’s energy needs.

In 2001, the US Department of Energy performed a detailed, nationwide survey of home energy consumption. Figure 1.8 presents the energy consumed by the average American household in 2001 according to end use. In 2001,

each American household spent an average of $1,493 on energy to heat, cool, and power their homes.

We ask a great deal from our homes. They need to shelter us in comfort in addition to providing heat, light, hot water, and all the modern conveniences and entertainments. And we expect all of this to happen economically over a long period of time — without an owner’s manual! You probably know more about the operation of your car or VCR than about how your house operates. In fact, we don’t really think in terms of the “operation” of our homes at all. We buy a house for price, square footage, location, and amenities. We optimistically assume that the builder and the building codes have taken care of everything else and that the house will “work.” Builders and building owners rarely envision the house as a whole, as a living organism with multiple, interdependent systems and functions, much like our own bodies. Very often, heating systems are installed almost as an afterthought, and indoor air quality is largely ignored. What you can’t see in a house sometimes matters more than what you can see. I’ll show you the inside of your walls later in this book.

Figure 1.9 indicates the type and percentage of energy consumed by American households in 2001.

Look at the largest area of energy consumption: electricity losses. These losses are due to inefficiency! Electric companies burn fuel to generate electricity. Losses in power generation, transmission, and distribution mean that three units of fuel energy burned at the power plant give you only one unit of energy at the outlet in the wall. This power system (the grid) is only about 30 percent efficient at delivering power to your home. And the problem gets worse inside our homes. The appliances we use are not very efficient either. An incandescent light bulb is only about ten percent efficient at converting electrical energy into light energy — the remaining 90 percent is lost as waste heat. When electricity generation, transmission, and distribution losses are added in, the overall efficiency of the same light bulb at converting the primary energy from the power plant to the actual light that you use in your home has dwindled to just three percent.

One way of addressing the inefficiency of power transmission and distribution is through what power companies call “distributed generation.” Distributed generation is where electricity is fed into power lines by small,

scattered power plants such as wind mills, solar electric arrays on roof tops, small-scale hydro power, methane captured at farms or landfills, or fossil fuel-powered turbines. The energy from these decentralized power sources tends to be used on-site by whoever is producing it, with the excess going out onto the grid for everyone else. Energy security analysts think distributed generation is preferable because reducing the demand on a single, central power plant makes widespread power interruptions less likely.

Another way to increase power plant efficiency is by way of co-generation (cogen) also known as combined heat and power (CHP). Co-generation means producing useful energy for more than one use from the same fuel source. For example, power plants generate enormous amounts of heat. Most of that heat boils water into high-pressure steam, which spins a turbine to produce electricity. Energy is lost in the process via low grade heat left in the water after the steam has passed through the turbine. If that heat energy is captured it can be used to heat the power plant, or even neighboring buildings in the town.

Your car is an excellent example of a co-generation power plant. It uses a single fuel source — gasoline — to produce mechanical power, electrical power, heat, and air conditioning. That still doesn’t make the car very efficient — only about 25 percent under ideal conditions. A huge amount of waste heat comes off the engine.

How do you choose the right fuel for the right task in your home? Is it time to switch fuels? Some questions to ask yourself are:

How do you begin to think about these issues? Let’s use electricity as an example. Electricity is available almost everywhere a house can be built and is probably the most convenient and carefree source of energy for your home. A heating element can be used to heat air by way of electric baseboard heat, radiant heat panels, a hot air furnace, electric clothes dryers, ovens, and toasters. Heating elements are also used to heat water in electric water heaters and dishwashers. Electricity requires no storage tank or monthly deliveries, emits no odor or local pollution, and needs no chimney. Installation of an electric space or water-heating system is far easier, placement more flexible, and is initially cheaper than an equivalent fossil-fuel system. Depending on where you live though, electricity is likely the most costly energy source, making it the least “comfortable” fuel if you can’t stay warm without breaking the bank.

Beware of low initial equipment costs when choosing fuels or buying appliances. It is important to consider the lifetime operating cost of an appliance because the initial purchase price is a small percentage of the overall cost of owning and operating almost anything over time (see Chapter 7 to learn

how to perform a life-cycle cost analysis). Space- and water-heating energy requirements can be substantial, and because electricity is typically the most expensive energy source, performing these tasks with electricity year after year can be more costly than using fossil fuels.

When considering alternatives to electricity, make a list of what fuels are available in your location. In addition to the sun and wind, these fuels are typically natural gas, propane, heating oil, or kerosene. You can find appliances that operate on nearly any of these fuels. Read more about the appliance in question in the appropriate chapter, and then talk to your local fuel dealers for estimates and about the practicality for your home. For the best price, many dealers offer a “pre-buy” plan where you buy all your fuel at once and don’t need to worry about price fluctuations during the year.

• What do you want to use the fuel for? Heating your house and hot water? Cooking?

• Do you only want one fuel in your home? Perhaps you like to cook with gas but heating oil might be cheaper to use to heat your home.

• You might want to consider gas (natural or LP) over oil because it burns more cleanly (less CO₂and other emissions per unit of energy used). See Appendix B for a CO₂production profile of fuels.

• Can the fuel be delivered to your home? If there is natural gas in your neighborhood, call the local gas company to find out if it is available to your home. If you need heating oil or propane gas, can a fuel delivery truck get to your home? Sometimes a bridge, steep hill, narrow road, or poor weather can prevent delivery of a fuel to your home.

• Where will the fuel be stored? If you use heating oil, the storage tank (typically 275 gallons) will probably need to be located in your basement or some other place that is out of the weather. A propane storage tank will be outside your home and you’ll need to make a space for it that both you and your supplier can live with.

Energy prices vary regionally, seasonally, and annually based on contractual agreements and market forces. The following section will help you determine the delivered energy costs for different fuels.

Too often I hear homeowners struggling with the question of fuel prices and how to reduce costs. Often, the term “bill” gets in the way. Just because you get two different fuel bills doesn’t necessarily mean that you’re going to pay more in energy costs than when you only had one bill. In fact, after scrutinizing their energy uses and costs, I often encourage folks to switch fuels for one or more items in their homes. Once you understand how to compare fuel costs and actual, usable energy delivered for that price on an apples-to-apples comparison (using Btus), the mystery clears up.

The Energy Audit

When I visited Ken and Connie Sumer on a hot day last summer, the first thing I noticed pulling into their driveway was that they had underground power lines. The electric meter was on a pole near the driveway, and there was no sign of power cables going into the house. This is not a problem, but it could be a clue to unexplained high use in older homes. More clues turned up.

Connie told me about how they had installed an in-ground pool last year and their power bill really jumped. Not surprisingly, I found out later that the pool filter had a one horsepower pump and they kept it on all day and night. I noticed that the pool was between the house and the power pole and asked them, “How long were you without power after the backhoe started digging?”

“Oh, what a mess — four days! How did you know?”

If your underground lines are damaged due to an excavation project, it is possible that a small amount of current could leak into the ground through a break in the insulation. In such a circumstance, you might notice a spike in your usage when the ground is wet. To help prevent accidental damage, all underground wiring should be encased in properly sized conduit rated for electrical use. If you have underground power lines, it’s always a good idea to call the power company before you dig. If you suspect a problem, an electrician can check an underground line with a meter without the need to dig it up.

I took a walk over to the Sumers’ meter to get a reading. The meter disk was spinning about as fast as my table saw! Air conditioner I thought. And pool pump. Maybe she’s cooking in the electric oven. But, geesh! I could cut wood with that meter dial!

With that in the back of my mind, I met with Connie’s husband, Ken Sumer, and continued on my house inspection.

Yes, the central air conditioner was on, the thermostat set for 68°.

“Too low,” I told Ken. “Are you from the north country?” I teased. “Look, your heat thermostat is set at 72° and if that’s good enough in the winter, why not summer too? In fact, if you really want to save energy and money, you should reverse these two settings — 72° or higher in summer, 68° for winter. And I’ve just solved your high use problem,” I boasted.

The heating and air conditioning thermostats were right next to each other. The heat was set higher than the air conditioner. The AC would come on and cool the air off to 68°, and then the heat would kick in trying to keep the place at 72°. You wouldn’t think it could get much worse than dueling thermostats.

But it did.

Junior came rollerblading into the living room and looked excitedly at the stranger. I knew that I’d be his next victim.

“Wanna see something cool?” he asked.

I bit. “Sure.”

He led me to the playroom with its wall-to-wall aquariums and terrariums. “I collect snakes.” He said proudly.

“Cool.” I meant the room — it was cool, almost cold. “Don’t snakes and fish like it hot?”

“Yeah, the tanks all have heaters in them. See those rocks inside?

They’re really heaters! You just plug ’em in.”

I rolled my eyes at the sight of fifty-two little electric rock heaters and twenty fish-tank heaters: 4,100 watts of connected load. I turned to Ken and asked, “Do you want me to do the math for you or do you just want to turn off the air conditioning in this room? You could take the family out to a four-star restaurant with the savings.”

“I wanna a cheeseburger!” Junior shouted.

I sought refuge in the basement. Ken followed along.

In the corner of the basement there was a big blue tank — a water pressure tank. They had a drilled well to supply water. I looked at the pressure gauge and watched it slowly descend. I asked Ken if there was water on in the house somewhere. Nope. The gauge bottomed out and then started to rise again. I could hear the pressure switch clicking, switching the well pump on and off.

“Time to call a plumber and have your water system checked out. You could have a bad pressure tank, or an underground water-line leak, or maybe a bad check valve on the pump, causing water to slowly drain out of the system. Maybe the water softener timer’s gone haywire. While you’re at it, have him check out this gray box. It’s for the septic pump, and the light’s been on for the last ten minutes. That means you’re pumping sewage from the holding tank out to the leach field. You may have a bad float switch in the tank.” By the end of this litany, his eyes were fully glazed over.

“Call a plumber,” I repeated. “Point him over here.”

Next, I noticed electric heat tapes on the water pipes. Evidently, the pipes would freeze in the winter and the heat tapes were to keep the pipes warm. They ran along the top of the basement wall and as I looked more closely, I could see daylight through the rim joist at the top of the concrete wall — apparently the remains of an old hose spigot.

“You need to seal up those holes and keep the cold winter air off those pipes. Use expanding foam and then insulate the rim band around the entire basement perimeter. You can then unplug the heat tapes and enjoy lower bills and warmer floors upstairs too.”

Turning around, I saw a wood stove and walked towards it.

“Y2K,” Ken said sheepishly. “But I do use it occasionally, it’s a nice heat you know, but dry.” (I side-stepped this comment but readers should see the discussion on heat and air infiltration in Chapter 6.)

“So how many cords do you burn in a season?”

Ken led me to the small room he built in the basement where the wood was stacked. “I just had a cord delivered as back-up in case the power goes out.”

In the middle of the wood-room hummed a dehumidifier. I stared. First at the dehumidifier, then at Ken, then at the pile of wet, green wood, then back at the dehumidifier. Ken reached for the tray to empty it out. “Gosh, I can’t seem to empty this often enough.”

“Smells good in here.” I said. “Green wood has quite a lot of moisture in it. And so does your basement. You might want to consider building a small, open-air wood shed outside — just to keep the rain off the wood. Stack the wood in the shed and after a year it will be dry enough to burn. You really don’t want to pay extra for your wood by drying it with a dehumidifier. And your basement is so damp that the wood might never really dry out enough to burn well.”

The basement was also home to the usual cadre of infrequently used appliances, including an exercise treadmill and an old refrigerator holding a single six-pack of beer and a single can of ginger ale, with a freezer filled with more frost than food. A sump pump sat in a pit in the corner. It was off. Just above it was the circuit breaker box. I looked inside to try to identify the big users in the house. I do this by identifying the 240-volt breakers (the big, fat ones) indicating an especially large electrical load. As I pulled the panel door open, it fell into my hand, revealing a nest of spaghetti-like wiring. Inside the box, I noticed that many of the electrical connections had a chalky white coating on them. One of the breakers was loose in its socket. I tried to push it back in and a few sparks flew.

“Time for an electrician,” I said, handing Ken the breaker box door. Bad grounding, poor connections, and corrosion can all lead to inexplicably high electrical use in addition to being a dangerous situation. Ken told me that the basement was prone to flooding and that’s why he got the sump pump. That’s probably why there was corrosion on the breaker box, too.

The amount of energy contained in a unit of fuel can be described in terms of its energy density. Despite their relatively small percentage of hydrogen, hydrocarbon fuels are very energy-dense, meaning that they contain lots of potential energy in relation to their weight or volume. The high energy density of fossil fuels makes them convenient to store and use almost anywhere.

Energy density is expressed as a measure of how much energy is contained in a given unit of a fuel. The units are usually pounds, gallons, or cubic feet. Here are the energy densities by weight of a few energy sources:

• automotive battery (including the lead, electrolyte, and case) = 55 Btus per pound

Expressing energy density in different units reveals other qualities. Using the same fuels, let’s switch units from weight to volume:

It’s easy to see now what the problem with electric cars is. It takes 345 pounds of batteries to store the equivalent energy of one gallon (just over six pounds) of gasoline. You can also see that 345 pounds of batteries occupies 187 times more space than a gallon of gasoline.

Hydrogen, which can be completely combusted with no waste, is a gas and not very dense. To make hydrogen easy to transport or store in useful quantities would take a very large container. To make the container size more manageable would require that hydrogen gas be compressed, and that takes energy. Natural gas (which is one part carbon to four parts hydrogen or CH₄) comes closest to pure hydrogen of any home energy fuel, but natural gas is only available where pipelines exist to deliver it. Compressing and transporting hydrogen or natural gas has not been found to be cost-effective for home use.

Embodied Energy

When considering the true cost and efficiency of an energy source, the fuel’s embodied energy should be considered. Embodied energy is a measure of the energy input that goes into producing an end product. For example, it takes a certain amount of energy and resources to extract a gallon of oil from the earth. The well-drilling equipment and processing infrastructure needs to be built, energy is used to extract the oil from its reservoir, then the fuel needs to be transported to and from the refinery (in a fossil fuel-burning truck or train). Finally, the end-user receives the fuel in the form of gasoline, oil, kerosene, jet fuel, liquid propane, diesel fuel, and others.

Embodied energy can be expressed as a ratio of energy output to energy input. This is sometimes called energy balance or energy profit ratio. For example, if it takes one gallon of oil to get two gallons out of the ground and deliver it to you, the energy balance of that gallon of oil is 2:1. When the energy balance ratio falls below 1:1, then it’s time to start looking for another, cheaper fuel source.

However, the actual embodied energy in a gallon of oil is not reflected in its relatively low price. Consider that a gallon of gasoline costs about the same as a gallon of milk, and not much more than water. When you think about the energy that goes into producing a gallon of each, you have to wonder why gasoline is so cheap, or why water is so expensive. Petroleum prices would be quite a bit higher if the industry — rather than the government — were required to pay for the security of its global product transportation routes. That cost is instead reflected in our federal taxes. So you can see that it can be difficult to draw a clean circle around the costs and activities involved in producing fuel to keep our homes warm and economy moving.

Consider the embodied energy involved in supplying a kilowatt-hour of electricity to your home. Energy is used to extract the fuel from the earth (coal, for example), and then to refine, transport, and burn it to produce steam to drive the turbines to create electricity that flows through power lines, switching stations, and transformers. Roughly two thirds of the energy in the original fuel is lost in the generation, transmission, and distribution of electricity. In addition, the electric company expends energy for the operation and maintenance of this infrastructure. Electricity is in fact the most efficient energy source to use once it gets to your home, but it is not very efficient when you consider all of the embodied and lost energy that goes into getting the power to your house. These losses add up to make electricity a very expensive (and wasteful) energy source.

As we’ve learned, the Btu is a way of comparing the energy content per unit of fuel (gallons, cubic feet, or therms). Table 1.2 lists common fuels and their energy content per unit. These units represent how the fuels are typically sold. Also included for comparison is the energy content of a typical lead-acid battery as is used in your car and in a solar-powered home, and a pound of enriched uranium as might be used in a nuclear power plant.

As you can see, home heating oil has 50 percent more energy than propane per unit volume. Propane, however, typically costs at least as much or more than heating oil. Figure 1.10 shows the cost per MMBtu of common fuels based on the average price of the fuel, and the Math Box shows you how to make the calculation yourself based on local fuel prices.

Note: Energy content per unit of fuel may vary due to additives, impurities and source.

This chart can illustrate why choosing the cheapest fuel per unit doesn’t guarantee that you will pay the least amount possible for the actual energy delivered. The price per MMBtu of useful energy will be affected by the efficiency of the equipment utilizing the fuel. For example, if your heating system is 75 percent efficient at converting fuel input to heat output, you lose 25 percent of your fuel up the chimney along with 25 percent of your fuel dollars.

Figure 1.11 shows the fuel price per MMBtu after adjusting for average equipment efficiency, and the Math Box shows you how to make the calculation yourself based on local fuel prices and your equipment’s rated efficiency.

As you can see, when equipment efficiency is taken into account, the net energy converted into useful work is reduced, and the effective price of the fuel rises.

The assumptions for fuel price and equipment efficiency in Figure 1.10 and Figure 1.11 are shown in Table 1.3. I have included the energy content of uranium here to illustrate both its incredible energy content by weight, and its

Gasoline is used only for illustration. The efficiency shown is for that of an internal combustion engine.Other efficiency figures are typical for heating equipment

overall inefficiency as a fuel. This inefficiency is primarily due to the fact that only about four percent of the fissionable material in the uranium loaded into reactors is converted into energy. Still, enriched uranium is incredibly energy-dense.

Let’s take a few minutes here to clear up any confusion between efficiency and cost. Efficiency is the ability to produce a desired result with a minimum of effort or waste. Mathematically, efficiency is the relationship of energy output divided by energy input, and is usually expressed in percentage. Nothing is more than 100 percent efficient. An electric water heater is very efficient (nearly 100 percent) at converting its electrical energy input into hot water output, and it is likely the cheapest kind of water heater to buy and install. This does not mean that the electric water heater is the most cost-effective way to heat water over the long term. Because electricity is an expensive energy source compared to most other fuels you can use to heat your water, a more expensive fossil fuel or solar water heater can cost less to buy, install, and operate over time.

To determine overall cost-effectiveness, you must consider efficiency (which affects operating costs), initial cost of the equipment, maintenance costs, and the lifetime of the equipment. To learn more about performing a life-cycle cost analysis for any energy using appliance in your home, see Chapter 7.

• How well heat is transferred from the flame to the air in a furnace or water in a water heater which is called transfer efficiency.

• How much heat is lost through the jacket, or housing, of the equipment which is called standby loss.

• How much heat goes up the chimney while the burner is firing which is called flue loss.

• Heat lost up the chimney while the burner is not firing is called off-cycle loss. This includes heat lost from the heating appliance along with heated air from the house.

The net price (after accounting for conversion efficiency) per MMBtu of gasoline burned in a typical (very inefficient) internal combustion engine is much higher than the purchase price. Most of the fuel energy consumed by your car is wasted as heat, a byproduct of combustion. The same is true for a gasoline-powered generator, a very expensive way to make electricity.

Math Box: Fuel-Switch Savings Calculations

To figure your own fuel-switch savings scenarios, follow these steps.

1. Decide what appliance you want to consider for a fuel switch and what fuel you want to use for the new appliance.

2. Determine that appliance’s energy consumption in fuel units (gallons, kWh, Ccf or therms) by looking at your bills, having an energy audit, or reading the rest of this book to learn to make a reasonable estimate.

3 Determine the operating cost of the appliance by multiplying the fuel units by the price per unit.

4. Convert fuel units to equivalent Btus of energy consumption.

5. Multiply the Btus consumed by the old equipment by its efficiency.

6. Divide the adjusted Btus (from #5) by the efficiency of the new equipment. This is how many Btus the new equipment will consume.

7. Convert Btus to units of the fuel under consideration.

8. Multiply the number of fuel units by the price per unit.

9. Subtract new from original fuel costs to determine energy cost savings.

For example: I want to know if it is worth while to switch my electric water heater to a natural gas water heater. I have read the chapter on electricity use and determined that my water heater uses 5,250 kWh per year (including standby losses) to heat water. The local utility charges $0.095 per kWh, so it costs me:

5,250 × $0.095 = $498.75 per year to heat my water

There are 3,413 Btus in a kWh (from Table 1.2), so my water heater uses:

5,250 kWh × 3,413 = 17,918,250 Btus per year

The efficiency of the electric water heater (in this case called energy factor; read more about this in Chapter 4) is 0.89. Multiplying total consumption by the energy factor removes the effect of standby losses and offers a level ground for comparison to the new water heater, with its own energy factor.

17,918,250 × .89 =15,947,243 Btus hot water demand

The new gas water heater has an energy factor of 0.63. Dividing demand by the new energy factor gives us total Btus required to heat the water, including standby losses.

15,947,243 ÷ .63 = 25,313,084 Btus total energy consumption

You probably noticed that the energy consumption has increased compared with that of the electric water heater. This is because the efficiency of the gas water heater is lower than that of the electric. Let’s see how this works out in terms of cost by first converting from Btus to new fuel units. Table 1.2 shows that there are 100,000 Btus in a therm.

25,313,084 ÷ 100,000 = 253 therms

I’ll need to buy 253 therms of natural gas instead of 5,250 kilowatt-hours to keep my family in hot water. The local gas utility charges $0.98 per therm, so to operate the gas water heater would cost:

253 × $0.98 = $247.94

By switching from an electric water heater to a gas unit, we will save:

$567 – $248 = $319 per year

With an installed cost of $900 (it’s a high quality, sealed-combustion model), the gas water heater will pay for itself in under three years.

Once you know what fuels are locally available, their costs, their appropriateness for specific jobs, and your needs, you can determine the most efficient equipment and the least costly fuel options for any task in any home. You can simply reference Figure 1.10 to get an idea of what the lowest cost fuels are, although these costs will vary widely throughout the country. To learn the intricacies of fuel-switch savings calculations, work through the exercises in the fuel-switch savings Math Box on pages 49 and 50.

Refer back to Figure 1.9. The biggest slice of the home-energy-use pie is electrical energy waste. There is little you can do about this at the power plant, but you can make a big difference at home, and you will see your efforts reflected in lower energy bills. Many small efforts add up to big change. One of the easiest things to do is to simply be aware of what is using energy at any given time and why. Our homes have many phantom loads, using energy that we may

be unaware of. As you will read in the chapter on electricity, a phantom load is an item that consumes energy even when it appears to be off. This is true not only for electric appliances, but for gas equipment as well.

If you have a gas oven, water heater, or space heater with a standing pilot light, you may be burning more money than you need to. The pilot light on your oven might use 400 Btus, your water heater’s pilot light might burn at a rate of 700 Btus, and a gas furnace could be as high as 1,000 Btus. Many new gas appliances have electronic ignition, eliminating wasteful pilot lights. If you’re shopping for new fossil fuel equipment, look for those with electronic ignition. If you’d like to figure out just how much a pilot light is costing you, see the Math Box above.

Heat is energy. The faster a substance’s molecules move, the more energy it contains and the hotter the object. As long as there are temperature differences, heat will move — always from hot to cold (from high energy to low-energy). The universe wants to be at equilibrium and until that happens, everything will be in some kind of chaotic motion, desperate for balance. In your home, this means that air you paid to heat is frantically trying to get outside and be at one with the cold.

There are three ways, or paths, by which heat can be transmitted. Your house exhibits all three of these types of heat loss, as does a tea kettle heating on a stovetop. Reducing heat transmission cost-effectively is the key to energy savings and increased personal comfort. These three heat transfer paths are:

Heat conducts through solid objects in contact with each other. The flame from the stove heats the tea kettle and heat is conducted through the metal and into the water. The hot handle will conduct its heat to your hand. More dense materials (such as metal) conduct heat better than less dense materials (such as air or insulation).

Heat transfer by a moving fluid like air or water is called convection. Convection happens because of density differences between warmer and cooler parts of the fluid. The hotter the fluid, the less dense it is. In the tea kettle, the water on the bottom heats up first and becomes less dense as its molecules begin moving faster and expand. These lighter molecules rise to the top of the kettle, forcing cooler, heavier molecules down. This motion is called convection. When you blow on a hot drink, convective heat loss occurs between the drink and the air. A cool wind causes convective heat loss from your skin.

Heat passing through space from one object to another is said to radiate. The sun radiates heat that you can feel on your skin. When you stand next to a cold window, your body radiates heat towards the window and that is why you feel cold –– heat is being removed from your body. The window doesn’t radiate cold towards you because heat always moves from hot to cold. The tea kettle will radiate heat to the air and objects around it until there is no temperature difference between them.

Specific, Sensible, and Latent Heat

Air and moisture are the two biggest components in our living environment affecting our comfort level. Each absorbs and gives up heat predictably, but differently.

The number of Btus required to raise the temperature of one pound of a material by 1°F is called its specific heat.

When one Btu of heat energy is added to one pound of water, its temperature rises 1°F. The specific heat of water then is 1. This relationship holds true while water is in its liquid phase, between 32°F and 212°F. For air, the relationship says that raising one pound of air one degree requires 0.24 Btu.

As we add Btus to a material, its temperature rises according to its specific heat. This relationship is called sensible heat.

Things get more complicated when materials change phase such as when water changes from liquid to vapor. When one pound of water reaches 212°F it boils, remaining at 212° while it slowly vaporizes into steam. With a specific heat of 1, the pound of water absorbed 162 Btus to go from 50°F to 212°F (212 – 50 = 162), but will absorb 970 more Btus to completely turn to steam. The pound of water requires six times more energy to allow it to change phase. The heat energy required for water to change phase — that is to boil or freeze, condense from the air or evaporate into the air — is called latent heat.

As you can see, there is a lot of energy in water vapor. If you can get water to evaporate, it will absorb lots of heat energy from where it is evaporating, effectively cooling the object. This is why we sweat. The heat released or absorbed when a material changes from liquid to vapor is called latent heat of vaporization and is a very efficient way of removing heat from our bodies. To get that water vapor to condense again releases the same amount of energy. If you want to freeze that pound of water, you would need to remove 18 Btus to cool it from 50°F to 32°F (50 – 32), and another 144 Btus to change its phase to a frozen block. This is called latent heat of fusion.

Latent heat of vaporization is the basic principle behind evaporative coolers and heat pumps (air conditioners are heat pumps). Evaporation removes heat from the source, while condensation releases the heat in the water vapor onto a cooler object. Think of your eyeglasses (if you wear them). When you come in from the cold, the eyeglasses fog up as moisture condenses out of the warm air and onto the cold surface, warming up the glasses (heat travels from hot to cold). Stepping outside again reverses the process as heat from the glasses along with the moisture now condensed on their surface is released into the cold air.

This is the same idea behind high efficiency “condensing” boilers or furnaces — they capture the latent heat of vaporization, which would otherwise be lost up the chimney along with hot flue gasses. Twelve percent of the heat generated by combustion of natural gas is water’s latent heat, so a condensing furnace can theoretically be 12 percent more efficient than a conventional furnace.

Now that you know how to think critically about energy use, you can apply this knowledge to reducing energy use in your own home. In the coming chapters, we will examine ways to reduce home energy use, increase occupant comfort, and also learn about how the systems within your home may interact with each other to support the individuals living in the home. We’ll do this by looking into the following areas:

Understanding how these components work individually and in combination will lead to a more intimate understanding of your home. You already know that your house has a distinct personality with its sometimes mysterious creaks and groans and its particular spaces — each offering a unique feeling.

Your home may be asking for attention. Do you understand its language? Can you make your home happy? If you do, it will return the favor!

Fuel	BTU/Unit	unit
Home healing oil	138.690	gallon
Natural gas	100,000	therm/Ccf
Liquid petroleum gas (LPG)	91,690	gallon
Gasoline	125,071	gallon
Kerosene	125,071	gallon
Coal	21,000,000	ton
Wood	20,000,000	full cord
Electricity	3,413	kWh
Hydrogen	52,000	pound
Hydrogen	333	cubic foot
Enriched uranium	33 billion	pound
Solar home storage battery	60	pound