Here's how to deal with this problem. It is called an Air Handler. It take outside air and passes it thru a coil. It also takes some of the air in the space and mixes it with the new incoming air, That keeps the operating expense within reason. the amount of air that is drawn from outside is proportional to the amount of moist, ammonia tinged, dusty air that is purged by the exhaust fans. The temperature that we are talking about keeping the barn at is above freezing. Not 60 or 70 degrees. It only needs to be kept warm enough that the chickens wattles don't freeze and the feed/water/poop doesn't freeze either. It's also important not to have the cold air blowing on the livestock too much as they don't do well in cold drafty conditions. The dry, heated, outside air that has been mixed with the heated air from the top of the space, should be introduced into the bottom of one end of the barn and pulled out of the barn by the exhaust fans. That way the poultry always has warmer air gently flowing across their space drying the poop and carrying out the moisture/smells/ ammonia dust. So an air handler equipped with a Variable Speed Drive to match the incoming air to the exhausting air would be ideal. Low maintenence, less chance of dust clogging the coil due to excessive dust, able to be mounted to outside or inside of building to suit the need. And the most important part, a big efficient coal boiler to supply the heat. I know of several that would fit the bill.