? which furnace????

What size batteries and inverter do you use, nofossil? And what will it run? I'm thinking at minimum, you'd need enough capacity to run the blower on the boiler and at least one pump to get the hot water away from the boiler. I think in my house, if I was able to heat the gas boiler vessel, gravity would handle heating the house, at least at a minimum level. Since I live in town, I'm guessing I'd probably need hours--rather than days--of potential capacity. Can you charge a marine battery with a car or truck?

Yes.

Although a proper battery charger is preferred. But putting power to it will charge it, if needed.

I'd really like to see a good inverter system (for a reasonable price) that will have two outputs - one that runs as long as there is power, and one that only runs when the power is over a certain level. That way, you could operate on batteries during a small power outage, but if the power dropped to a certain level, it would switch off the combustion fan and just run the system to cool the boiler.

Joe

I have a pair of 1000 watt/hour batteries. I'm still messing around with the setup, but the intent is to run the controller, and let the controller decide how long to run the fan. My design goal is to be able to be comfortable for 24 hours with no power and without firing up the generator. The circ pump is the biggest draw since it runs non-stop.