We built a 1 1/2 20' in Alaska. The smallest Kuma oil stove maxes at 18,000 BTU. It keeps our cabin at 50 when it is -15 outside. We have lots of windows that we have yet to curtain. The problem is when we arrive up and it is 0, it takes a long time to heat all of the cabin surfaces. We boost with a 30,000 BTU radiant propane heater to speed the process and then switch to just oil. It burns 2.5 gal per 24 hours at 18,000BTU.