I would have agreed with the notion that "these heaters don't work that well anyways" until I drove home (in 2007) a ragged 1954 pickup that I had just bought. It had been shipped from WA state to NJ and I had to drive it about 180 miles to my home near Albany, NY (in December). The truck was supposedly drivable, but the brakes were dangerous and the steering was loose. The windows and doors rattled and it had no seals/weatherstrip/windlace. It was 8 degrees F outside and I had the foresight to bring multiple layers of clothes and a down jacket with hood.

To my enjoyment, the original recirculating heater was able to keep the cab so warm that I was able to drive comfortably in my shirtsleeves with no gloves.

The original Fresh Air (Air Flow style) heater in my 1954 Suburban more than adequately heats the truck, clears the windshield, and it had a variety of settings.