p.s. - We had a chance to push both our RV furnace and vent-free heater very hard last fall when we were at 10,000' elevation in Colorado in a snowstorm.
I talk about that in detail on my page about
vent-free propane heaters.
In a nutshell, the temps outside were in the teens at night and 30's during the day. The RV furnace ran full-time and couldn't get the buggy's temp above 50 degrees. In 30 minutes, the vent-free heater got the buggy's inside temp from 50 to 70.
That elevation is tough for any propane device due to lack of oxygen, and the vent-free heater's sensor shut the heater off several times (all vent-free heaters are built with sensors and auto shut-off valves) although our stove and oven kept going strong (they aren't built to the same strict specs!). This was easily remedied by opening the RV door for a few minutes.
All in all, it was uncomfortable no matter how you played it. Best solution would be an RV park with free electricity and an electric heater, LOL! But it was interesting to see the two heaters side by side in relatively extreme conditions they weren't really designed for!