These were air-cooled and the hot air from the engine cooling blower was piped into the passenger compartment.
Anyone remember the very first Honda Civics? Air-cooled 600 cc engine. Gearshift stuck straight out of the middle of the dashboard. No AC, no radio, nothing but heat, which was just a vent in the firewall. When you opened it up, it did get warm--and also really noisy. I could lift the rear end of the car clear off the ground. At college, the typical prank was two ore three strong guys would pick up the whole car and turn it 90 degrees in the parking space.
It also got nearly 60 MPG...