How to heat

Evan Dutch said
that sounds interesting, can you give me an example?

Many unit heaters use "outside air for combustion." I can't provide specific models, I have not been in HVAC for over 20 years. "Back then" some of the home heating high efficiency furnaces were sealed/ outside air. A very quick search gave this example

Hot Dawg Separated Combustion Heater

This from Modine

Commercial Gas Fired Unit Heaters | HVAC

Look for terms like "separated combustion chamber", "outside combustion air" or "sealed combustion."