I am looking to purchase an infrared propane heater for my calving shed. Most winters i have used nothing but sometimes if it is brutally cold when i am calving heifers i would run my space heater but i hate it because i am afraid of starting a fire and it is loud. I am looking to mount an infrared from the ceiling. I am not planning on trying to keep the barn heated I just want to be able to take the edge off the worst days. My calving shed is a 24x40 Morton building. with 9' side walls and no insulation. What do you use or how many BTU's should i get?