Back when I used light bulbs to heat the RO closet, it barely needed 1at 100 watts, but I had 3 100's (and they were on a line volt t-staT, SET AT 40f) to be sure. I now have a 8000 BTU wall heater, direct vented and the line volt t-stat has a 1200 watt electric heater for back up, and that circuit is on a solar bank and inverter in case the grid power goes out. The propane thermostat is set at 43F and the electric is set at 40F backup.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.