[pgryko]

I'm also open to ideas. My girlfriend's elderly parents are based in Irpin, so I'm worried about heat outages. I've got them a battery powerstation, but even the large ones seem to have a limit of ~1000 watts, whilst a small heater pulls 2000 watts.

I'm contemplating getting a diesel generator, to share amongst them and their neighbours, but it's less than ideal as the generator has to be outside (for ventilation) and their apartment block doesn't have balconies.

[simne]

This depend on what exact tech is used in heater. Many old heaters are just Ohm heaters, for them working Ohm rule: power is proportional to square of voltage, and simple transformers are extremely effective - 90% is normal (sure, 2000W transformer is not small, but affordable), so if you will just use transformer to transform voltage from 220 to 120, your 2000W heater will effectively become 2000/((220/120)*2) = 595W, so 1000W powerstation could feed it (transformer should be for larger power than feed, 2000W will be normal for case of 2000W heater). Even exist regulated transformers, but I don't recommend they for people without electric education.

For heat pumps (fridges, conditioners), boiler automation, microwave, modern high frequency furnaces, things are more complicated and this will not work directly, but for them usually written MAX power input, but in reality they consume max power only few seconds to start, and all other time, typical 1/4 of max power or even less. So, you need to check peak power output of your powerstation, many have constant power for example 1000W, but peak 2000W.

In some cases, may be good solution automobile booster, as they designed to have insane high peak power.

I could not recommend this, but in many cases, in modern tech, only digital part is much depend on voltage and consume very little power, and use closed loop control and sensors, but heaters are just old Ohm heaters, and they connected with digital by relays, so it is possible to power digital part from external power supply, like mobile charger (international variants usually work 100-240V), and heaters directly with lower voltage (120V instead of 220V).