I suggest a Generac back-up generator which could be powered by your propane tank. You would need a very large generator to power the electric boiler. If you don't want to make that big an investment then it could be sized to power the rest of the house only. You would some electric space heaters to keep the house comfortable while waiting for the power to return.

My home is heated by NG and during this carfuffle on the Texas grid, we ran a generator and space heaters. Not a perfect solution, but we didn't freeze nor do we have pipe bursting issues. It is my intention to invest in a large enough generator to power the whole house. Sadly this is happening far to often.

No fireplace?

I can reduce the amount of electricity necessary for a backup generator by turning off one or more of the heating units in my boiler (need to check with the mfr. and see if that is doable). My house is wired weirdly - the builder decided that one 200A service was insufficient, so rather than increase the size of the wires going from my meter panel to the house, he ran a second set to a second 200A panel, to which my boiler is connected. I don't know what rewiring would be necessary to put in a transfer switch.

Right jrb, no fireplace. We didn't have a good place to put it, not wanting any breaks in our superinsulated roof, and wanted to keep the amount of burned gasses in the house minimized. Also, that wouldn't work if we are not at home.

How about a large Generac-type standby permanent generator installed to run off of propane? I know there needs to be wiggle room between output and load, so maybe you'd need a 30Kw generator for a 20 Kw boiler? The manufacturer would know. Such generators are wired with a device that automatically cuts off the panel from the grid when the generator comes on, and re-establishes the grid connection when the system powers back on and the generator turns itself off.

Maybe $15-20K installed. Just a wild axx guess. But other than in the case of a rare problem, these as close to bullet-proof reliable as you'll find.

Your two electrical panel set up could work out nicely if you want to install the transfer switch for the whole house and not the boiler. I think that would be a reasonable compromise between cost and comfort. But you could also go for everything as Elmer has suggested. You have to decide how much money you are willing to spend.

Hmmmmmm.................... the Minisplit warehouse spambot ^^^ missed the mark yet again!

Without electricity, it doesn't matter what his backup heat is or "as a responsible homeowner, you should really know how this setting works and when it should be used appropriately".

He wants to know how to get some heat into his home when the electricity goes out (and none of the aforementioned emergency heat systems will work).

I remember the ice storm of (January) '98. Near the shores of Cayuga Lake, power was not reliable (and mostly off) for days even though local damage was much lighter than up in the 'daks. I was on well water at the time and an oil-fired boiler supplied heat. I'd leave lights and a radio on to wake me up if the power went on so I could do get up to do some dishes and laundry. I was out all day at work

How much power is lost in the conversion of propane to heat more directly vs. running a genset powering resistance heat? You might be able to come up with a ducted propane furnace installed in a shed to provide back-up heat Lots of insulation on the ducts could make hot air transmission pretty efficient. The furnace would not need be very large or efficient given that you only want to prevent freezing. It would require electricity, but not much. A very small genset would do, but I don't know how small you can go and be automatic. I guess you want some kind of generator in the case your PV system is damaged.

The switch gear to provide power to partial furnace coils would be a custom thing, but not nearly impossible. Since you have a solar system you have a big advantage in that you can either use and AC genset at nearly full power or off while draining and charging batteries which would save a lot of fuel. Alternatively, and probably better, if DC gensets are a good alternative at this point, they can run at the rate needed to keep the batteries nearly fully-charged saving fuel and long term battery capacity. Either way, good integration with your PV system would pay off.

Thanks for your comments, ionized, you have several good ideas. I don't have batteries at present and am trying to decide between them and a genset. Simplest system would be a genset near my meter panel. This is about 200 feet from the house, and has a large propane tank near it. I had one "guestimate" from Lowes of $20k, not including installation. If I spent that amount on batteries, how much energy would I be able to store? As I said earlier, my PV system has a maximum output of 14kW. So far, this year, the weekly energy production has ranged from 115 to 300kWh (January and February). Looking up some information, a single Powerwall ($8000) will provide 5kW of power, with a storage of 14kWh, so based on the power availability of 5kW each, I would need 4 to power my 20kW boiler; that would cost $32,000. And, my pv system could charge it in a couple of days.

My boiler has 4 separate heaters with individual breakers, so if I turned two of them off, I could cut those numbers in half.

If there were a moderate snowfall, would your solar cells be covered or would they remain functional?

I'd think a permanent generator setup could be relied upon to function independent of weather conditions, whether or not you're there.

Yes, when it snows, but the panels shed the snow pretty quickly (the roof is at 45°). I am, however, inclined to agree with you about the generator.

To ionized, if I determine that the boiler will run with half it's heaters turned off and produce enough energy to keep the house above freezing, I would turn off two of the heaters when I leave the house, so the transfer switch would not be involved.