I have a small ventless gas heater that will heat approximately 1000 sq.ft. For a short period of time, we can get by with that and the gas range in the kitchen. As for the number of KW hrs, I checked our usage for the past year and we never used less than 750Kw hrs. Our average was about 1500 Kw hrs. per month, with the high being in July of this year when we used 3000 KW hrs.
Our lowest consumption was in May of this year when we used 930 Kw hrs. May was unusually cool and July was unusually hot.