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> The blower motors are pretty power hungry, on the order of about 330 watts, give or take. For a 12V system that is about 30 amps, or about 2 hours of output from a typical deep cycle batter before you risk depleting it to the point of damage. An ~$300 12V Lifepo4 battery might get you 4 hours of runtime, but not much more than that.

This is 2-4 hours of run time though. My experience is that the blower turns on for a period and then off for a period. It would depend on your heat loss rate which is situation specific, but you can probably get significantly more than this in time coverage with the blower only running periodically.

I have a 7500W dual-fuel generator but haven't gotten around to installing a transfer switch yet. I have a well pump and a gas boiler that I really miss when the power is out :)

Radiant in-floor heat is pretty efficient (and it's nice not to have an ice-cold floor first thing in the morning), just need power for the circulation pumps and the boiler. My back up heat is a wood-burning stove - and we have lost power for several hours when the temps are -20F or so...

> power for the circulation pumps and the boiler

If the boiler is in the basement would you not be able to treat the circulation tubes as a thermosiphon, with the hot water rising from the boiler, creating pressure to push water through the loop?

> TL;DR - Your deep cycle battery approach may not prove to actually be worthwhile, consider working out the car-as-generator hookup plan in advance.

Ha yep, learned that the first time and was ready to go with an extension cord the second time I needed this setup. First time, I had a stash of 3 batteries but I didn't realize how much power the blower motor would draw, so I was charging on the car and swapping out batteries as needed. Did that the first day then rigged up cords for day 2. Halfway through day 3 we got power back.