My chicken house addition was built from recycled rough cut lumber that was rescued from an old lumber camp my husband helped tear down. The rough cut wood was still 2″ X 6.” Modern planed 2 X 6′s are really only 1 and 3/4″ by 5 and 3/4.” That is why they had to change the spacing between the studs in modern walls to 16″ instead of the 2′ or 24″ that they used to be. Since I had real 2″ X 6″ wood I built with 24″ center to center spacing.
I researched wherever I could to learn about ventilation for chickens when I decided to put an addition on the shed. I wanted to increase the size of my flock. I found such suggestions as “one square foot of vent per bird.” This would be almost 1/3 of one of the long walls of the 8′ X16′ addition, or the top 1/6 of each long wall! This would be totally absurd in a building that I am going to heat in -40 degree weather. But search as I would I didn’t find anything helpful that would work in our cold winters, just saying how important ventilation is. I hadn’t settled on what I was going to do for sure, but I had to hurry and get the addition built. If I didn’t I wouldn’t have any place for my new birds, which I had been raising all summer.
So I built it and left the door open onto the chicken yard all that late summer and fall. Then winter hit. I had to close the door and keep the chickens in out of the snow. It soon became evident that I had to make up my mind about what I was going to do. When I went in, it was like stepping into a sauna. It is really amazing how much moisture the lungs of 30 large birds can produce!
I could not find anything about ventilation for chickens, but I had been researching ventilation and heating alternatives for passive solar houses. I had read a fair bit about air-to-air heat exchangers. Only they are complicated to make and energy intensive (using fans) not passive. They use fans to force fresh air from outside in, and blow out moist dirty inside air. The two streams of air are separated by a membrane which allows heat to pass from one stream of air to the other without the air mixing. Thus the outside air is warmed and the inside air is cooled. So most of the heat is retained in the building but the moisture and pollution is vented out.
I thought about some of the basic laws of physics which I had learned about in school. One is the law of inertia; that a body in motion tends to remain in motion. And the law of conservation of angular momentum; that something that is moving in a certain direction will tend to continue moving in the same direction. Another is that cold air falls and warm air rises.
I got to thinking. Air particles that are warm will try to rise and will probably continue to rise, even if more slowly, as it cools, if the distance is not too far, and even if the particle next to it is going in the opposite direction. And falling air will continue to fall even if slower as it warms, if the distance isn’t too far. And yet the distance needs to be long enough for the heat to exchange before the inside air gets out and the outside fresh air gets in. Maybe this would work even if the two air flows were intermingling. I got an idea for a sort of crude passive air-to-air heat exchange system.
Time To End The Sauna
The first two vents I built were put in during winter in the shed where there was damage to the plywood. The first was high on the wall by the corner with a 4″ opening out. The air was warmed fairly well but not as much moisture came out as in the 6″ opening which was lower on the wall and didn’t warm the air enough. I could tell how much moisture was coming out because it would form frost on the wall outside till the sun hit it. My husband remembered one of his teachers saying that if the ‘out’ opening was larger than the ‘in’ opening it would increase air flow. Neither of these was successful, and they were in what was going to be the unheated bedroom of the floor plan. I closed them off, but they looked like I might be on the right track.
What I did was locate the wooden studs behind the plywood. Using a jigsaw and a Sawzall saw I cut the plywood face just at the bottom of the top plate of the wall, over to the studs on either side, and down 6 inches and removed the insulation from the space. Then I cut a piece of 2 X 6 the exact width of the space between the 2 studs, fitted it into the space pushing it down till the top surface was just even with the edge of the hole through the plywood faces and fastened it in place with screws from both sides. Whenever possible I build with screws instead of nails because they are usually more reversible for repair and remodel.
Then on the inside I put an 86″ 2 X 4 on edge against the wall on each stud and covered the space between them with an 86″ by 24″ piece of 3/8″ plywood. This formed an air passage just under 2′ wide and 4″ deep and 86″ long. This air passage became 6″ wide as it made a right angle turn from vertical to horizontal when it came to the top of the wall and exited out through the 23″ X 6″ hole I had just cut.
I put a vent in each of the 2 spaces between the studs closest to the outside door of the addition. I am still not sure why, but the one nearest the door did not heat the air as well and wasn’t venting much moisture, but the next one did fine, especially after I took off the window screen and put on wire mesh with larger holes that didn’t clog up with frost and dust. It was still too moist so I opened a vent into the 3rd space. Two worked fine. The corner one was noticeably not working as well
All of them had a 4″ deep spacing between the plywood shell and the wall and a 6″ deep exit hole through the wall to the outside. What was different about the end one? It is the farthest from the heat – can’t be changed. It is closest to the door – can’t be changed and why should it matter? It is about 20″ wide instead of 24″ because of how the two walls join – that shouldn’t matter. The plywood stayed wet at the bottom – evaporating water cools air.
Vents #2 and #3 were working well but nothing I tried seemed to make #1 work as well. Suddenly the weather report said that our annual few days or a week of -40 degree cold weather was going to hit by the weekend. It had been fairly mild so far. I made a decision. I shut off #1. The weather did hit -40F at night and -30 during the day for a full week. When I put my hand under the #2 and #3 vents I could feel air movement, but almost no change in temperature! Frost was definitely showing around the opening outside and the humidity was way down. Success!