Warpspeed
Solar Wizard
I built myself a natural gas powered "Frankenstein" tumble dryer about ten years ago. That is what the new heat pump dryer is now replacing.
Fully functional Rinnai natural gas room heaters could be bought (at that time) on e-bay for scrap value.
Over time, I bought several for $50 each, and sometimes even less. They still appear occasionally, but not not as often these days.
These have a fully enclosed burner and use a heat exchanger. Outside combustion air has its own combustion air blower and the flue obviously also vents outside.
There is a separate room air blower which blows room air through the heat exchanger.
A bit of measurement showed that both the CFM air flow volume, and discharge temperature were about the same as my resistive tumble dryer
I cannot remember the CFM airflow figure, it was a long time ago.
But as I remember, on low heat the discharge temperature was about 50C.
So in a moment of complete madness, I coupled up the gas heater to the tumble dryer. The 2.4Kw heating element was disconnected and a 240v relay connected in its place. The relay contact fooled the room temperature sensor into firing up the Rinnai gas heater, and it all worked far better than I ever dreamed possible. It all worked perfectly including the cool down cycle along with a massive reduction in electricity consumption.
Natural gas here is very cheap by world standards, so it was a definite winner as far a running cost goes.
It was a very ugly piece of hardware, but the results certainly justified its existence.
The whole mess both heater and dryer cost me under $100 to put together, and it has lasted ten years
