This weekend was our last planned camping trip and I managed to kick it off with a klutzy move.
Friday night the temps got down to about 30 degrees, so we went to sleep with the furnace on and set to 60 just to keep the edge off. About midnight it shut down and all of the rest of the electrical was dead too. No power.
We heated in the morning by turning on one of the stove burners for a while
I felt really flummoxed that a fully-charged battery (even my crappy low-AH one) would be drained after only 5 hours of intermittent use of the furnace. Low and behold, it turns out I had forgotten to turn off the DC power on the fridge when I turned on it's propane after arriving. That explained the rapid power usage at least.
I hooked up the car and let it idle for about an hour as a make-shift generator to get enough power for basic lights and such. We also figured we'd run the furnace (30 degrees outside again) and make the best of it.
So, now that you have the back-story, here's the warning/advisory.
Furnace was purring along great, kicking on for a while, resting a while, and keeping it at a comfy 62 degrees or so. About 3am, the smoke alarm goes off. We leap up, see nothing on fire but can smell the acrid furnace smell like when we first got it (the smoke detector would go off then as well until I had ran the furnace several hours to burn off the oils). I quickly open the roof vent and only then notices that the lights are super dim. Looks like the power drained again.
My thinking is that as the power wound down, the furnace fan slowed down enough that it wasn't getting adequate air flow any longer, and hence the acrid smells. Not sure how hot it would have gotten if we hadn't been woken up.
I want to do a more controlled test at some point to see if I can correlate this behavior to low power, but I wanted to pass along this experience since we're heading into heating season.
At least in the spring I'm planning a power-system upgrade with solar and two batteries, so we'll have more capacity and passive recharging as well.