Sounds like you have a couple of scenarios to consider.

-Power outage
-Furnace broken

For a broken furnace, an electric space heater may prove useful.

If you find yourself in a situation trying to keep a little one warm, bundle them into your jacket with you. Your body heat will defintely keep them warm enough.

If you insulate a room well enough with blankets, you would be surprised at how much heat a candle can provide. Those 7 month olds are pretty robust. My little guy is 10 months now.

I would imagine you would only undress them to change them. Beyond that, keep them in a snowsuit or bundled with you.

Do you have a gas stove? You can turn on a burner and light with a lighter (preferably one of the long ones). I would have the lighter going first tho. That would also provide heat and doesn't require power.