Obviously this was inspired by the other thread but I didn’t want to divert that. I have a sauna in a cabin built onto the back of my garage and was wondering if I could use the heat from that for something useful.

When I finish a sauna after a ride all of the heat that has built up in the sauna is just lost to the atmosphere.

There is no much point in using it to heat the garage as it isn’t insulated and no-one will be there. I have a heater to use if I am spending much time in the garage but I was thinking I could use the heat to dry my shoes / camelbak etc (Stuff that isn’t washed each time) after the ride?

Ducted crossflow heat exchanger?
They use them in new builds for recovering heat from bathrooms etc. Not sure how you’d adapt it for something useful though.
https://uk.grundfos.com/service-support/encyclopedia-search/cross-flow-heat-exchanger.html

I got as far as looking at this

Look at what Finns do then try and copy it.

I will ask my mates if or how they do it.

^On modern houses the dirty air from outgoing vents is captured to fixed cell or rotating cell heat exchanger which then heats incoming fresh air. During coldest times this is not enough to warm the incoming air so there is extra heater too, either electric or liquid filled radiator.

Keeping it simple would make most sense, if you have wet laundry just put them in sauna after use. Drying laundry in the sauna is one of the most common causes of household fires though.