Thanks to "preventive maintenance" apparently 1 or 2 of our power plants are offline. So we have rolling blackouts - last round was 3hrs no electricity and 30minutes with. Earlier today we had 12hrs without, 1 with, 1 out, 45minutes with.
Net effect is I got the house from 50 to 57 during the last burst of electricity. Luckily 50 is the lowest we have hit so far and that is quite comfortable.
When I was looking at a fireplace for my new house, I noted inserts are a lot more effective than most ornamental fireplaces. Wood burning stove are probably more effective than inserts. There are a few fireplace designs that are very effective, but they generally cost a lot more than an insert or a wood burning stove. They tend to work by having a more complicated flue system within a very large thermal mass of stone/masonry. My favorite was one design. It was a tiny burn chamber coupled with 5-10 tons of thermal mass. A 30 minute very hot burn (self cleaning) would radiate heat for over 12hrs. If you really needed a LOT of heat, you could do 2 consecutive burns. Even then the radiating stone stonework would not be too hot to sit on.