I designed my heating system around a fairly efficient non-condensing NG boiler that takes 40W for the fan. I can run it and the circulators off my battery bank no problem, and handle a sustained power failure. But only because of the natural gas.

I've been integrating a water-water GSHP into it to provide summer cooling and a supplemental heat source from my solar panels. It works well, but in my climate (Rural Canada) I would be insane to completely remove my gas boiler IMO. Heating demand is just way too high on the sort of days where the power goes out. I've been working on plans for a wood boiler but insurance has put their foot right down on anything that burns wood in the last couple years.

Here in Canada we can't get lithium at a reasonable price so I have 10kWh of lead-acid (which as you know is actually 5). Doesn't go very far on a cold winter day with 4 hours of sun and snow on the panels!

On the upside I haven't had to hook my generator to my house in years, I'm really happy with my "grid-independent" system.