Sounds like a good low-cost product. A duct, a box and a few rails to hang the clothes on.

The citation is that they use a heat pump. They’re 3-4x as efficient at heating compared to resistive heaters.

Tumble dryers can also use heat pumps now.

99.9% of them do not. “Tumble dryer” means resistive or gas heating unless otherwise specified.

What are you talking about? Even ten years ago heat pump dryers made up 43% of dryer sales in Europe, and it's only gone up.

https://storage.topten.eu/source/files/EEDAL15_Eric_Bush_Hea...

Well that's interesting, I didn't realize it was so different in the EU. I suppose differences in energy prices and political willpower might explain it. In the US, the idea of a heat pump dryer is still more or less a foreign concept due to the price.

Or the heat released from the back of a fridge. I always wondered why nobody made one that used that heat for some purpose.

I've seen houses where the heat from the fridge vents to a drying cupboard on the floor above.