If our power is out too long, I bought a power inverter we can hook up to my car's battery to power 1 of our ceramic heaters. If that's not sufficient, we'll just keep the birds on us since they can get heat through their feet.
Based on that wording, it sounds like your inverter connects to the accessory/cigarette socket, which is limited to about 200 watts.
Larger inverters need to be hard-wired directly to the battery.
Ceramic space heaters are typically rated at 1500 watts, which would drain most car batteries in 20 minutes (assumed battery has a 100 Amp Hour rating, but it's likely less).
Throttling that down to the 200 watt accessory socket limit (if possible), would drain the battery in 2.5 hours if the car isn't running.
Your home won't lose enough heat in 2 hours to make that necessary, so that means you'll need to run the car's engine to extend the heater's run time.
There are many variables in determining how long a car's engine will run at idle, but to keep the math easy we can use 1 L/hr, so a 50 L tank will run for 50 hours.
A small fuel efficient engine will use less fuel and run longer, while a large displacement engine will use more fuel and run shorter (although the larger displacement engine will also likely have a larger fuel tank to compensate, but.. only if its tank is full).
Lastly, you'll need a long long enough cord to reach the car while it's running safely outside, and a way to route it inside to your heater which doesn't cause your home to lose extra heat (cracking open a window or door).
Disclaimers:
- I'm not an electrical engineer, so the figures may be off, or completely wrong
- I'm a nerd, and was curious about the feasibility of this option, and am simply sharing my though-processes in that exercise.
- BUT, I've conducted numerous disaster recovery tests professionally, and would suggest testing any such solution,
before you need to count on it.