Before I had frogs, house lost power one night while asleep during winter. When I woke up the house temperature was in mid-50s and dropping. Lit-up the gas fireplace and got common living/dinning/foyer area to high 60's. Power loss lasted 8 hours and my mature fish survived (in large tanks) but a brood of couple hundred Half-Moon Betta fry in a half-filled 10G perished.

Guess the best thing to have is a back-up generator; but some of us can't afford or install one. If you have a regular wood or gas fireplace, can light it and move enclosures into that room. If gas and clean burning (mine is), can close vent to send all heat into room.

If all animals are in one room, there are portable gas heaters that produce no dangerous fumes (at least to humans) and could be turned on inside a room. Burner heaters are a fire (if tipped) and child hazard (get hot) and you have to consider that in plans. You could also cover enclosures in blankets to prevent heat loss; but if power loss goes on for more than a day, think it will get to room temp inside the enclosures eventually.

The opposite situation is actually worse. A power loss during Summer in a warm area could easily wipe out many frog species in enclosures getting in the mid 90s or even above. Unless you have a generator that can run the AC or an unlimited supply of ice; you have an environmental disaster in you house . Just some ideas, hope it helps !