Heaters were/are exhausted into the building to reap the exhaust heat,not to add moisture. Moisture in a chicken house is already at high levels,none needs to be added. On a coal burner properly set-up not much heat is lost up the stack so no need to poison the indoor air. Wallyp ,if you install a coal boiler & pex the hot water to modine style heaters you can : heat safely,economically,eliminate the excess moisture issue & actually help to keep the building healthier for the chickens. Is the 450k btu for each house ?? You do not need to go to chineese junk to get a big heater, EFM & Van Wert make BIG boilers & there are some other brands too with HUGE output,( look in the pics of your boiler threads). If you are heating multiple buildings within reasonable distance of each other ,you might consider a HUGE unit to supply multiple buildings.Either way,furnace or boiler you will be able to improve the air quality & cut the energy bill by drier air resulting in less run time for exhaust fans & no propain !!