My tack room is 11x11, VERY well insulated with concrete floor, insulated door and 1 window. The ceiling is also 11’ high… A simple oil filled radiant heater, on the lowest setting (750w, level 1) keeps the room 70* or warmer when the outside temps are above 20*. When it dips below 20* outside, I bump the heater up to “medium” (1000w, level 1) and it keeps the room at 70*. The ONLY time I have needed the 1500w, level 6 setting was when I needed to warm up freshly born goat kids that were soaking wet on a windy 0* day. The tack room maintained 88* overnight that night!
I can blow the heater clean each fall before I use it with my force-air dryer. I never smell burnt dust/hair when I start it. I love that I can roll it out of the way when I don’t need it, and if it does quit working, it is $70 to replace vs. service calls and $$$ parts for a in-floor, in-wall or mini-split system.