Most cars in the 30s in Sweden had no heater, few of them was used
during wintertime. And there was a few trix if you used it, alcohol on
a rag to wipe the windshield for example or burning alcohol in a tincan
Later there was a lot of different after market heaters you could buy.
One was the underseat heater like a house radiator under the seat
that eventualy leaked and fogged down the windows and rusted the floor
When my dad bought it in 58 there was no heater in it so he installed
a heater from a Volvo PV444 and electric wipers from the same 444
The water heaters in say a Volvo from the 50s is enough for temperature,
problem is defogging the windows