Do you realize that on a cold windy day you are probably losing more heat through cracks around your side wall curtains than you are through your timer fans? For example, let’s say it is 400F outside, the wind is blowing 10 mph, you have day old chicks, and two 36" fans are set to run one minute out of five. In this situation 192,000 Btu's of heat are exhausted through timer fan ventilation each hour. This heat loss is necessary to insure that you are bringing in enough fresh is to keep the li...tter dry and the birds healthy. But, if you have just a half an inch crack between your curtain and side wall, you will lose an additional 507,000 Btu's of heat each hour. This additional heat loss increases your fuel bill and makes the house colder and draftier (The burning of one gallon of propane will produce 100,000 Btu’s of heat).