Your favourite spot for Tempeh incubation and other ferments requiring warmth (winter problem) ?

Hello fellow Permies!

Reading the sourdough starter thread, I stumble upon something that grabs my attention and keeps on nagging, so I need to ask:

For all your ferments, what is the go-to warm spot in your household to keep the ferments warm and cozy and producing the yummy pro-biotica we love so much?

I've created a little shelf (with cob) next to our rocket mass heater bell, it's also sitting over the exit-side of the exhaust tube, that is nice and warm without being too hot. The only problem is that it actually isn't big enough (!) and I should make it more level.

But what is your favourite spot to cheer your ferments on to greater growth?
Looking forward to reading your ideas :)

My vegetable ferments sit out on the kitchen counter year round and are much slower over the winter.

Tempeh, because it is more temperature sensitive, gets a more controlled environment in our large toaster oven (not plugged in), heated with bowls of water and insulated with towels as explained here https://permies.com/t/150194/making-tempeh

and my weekly raw milk yogurt incubates in our electric dehydrator at a controlled 105F.

If you are looking at Saana's sour dough thread you will see I had a problem keeping my new starter warm enough.  Now that it is active and more mature it is much easier to maintain.  I usually feed and keep refrigerated and when I plan to use it set out for a day first and it seems to work fine even in our cool house over the winter.

We have a workshop spot with radiant floor heating. Our ferments go on a seed starting matt set on a pallet. That is enough to keep ferments above 70ºF, with the thermostat set at 58ºF. A good trick, if you don't have radiant floors, is to make a plywood box and line it with rope light.

Judith and E, those are awesome ideas, thanks for sharing!

And as extra bonus I can now dip into tempeh-making experiences :) I tried to search for "tempeh" but the forum search machine didn't come up with anything else than the sour dough starter thread.

This is such a great and supportive site, thank you Permies!

I actually sometimes have less of a problem finding a warm spot in winter, because we have the wood stove on almost all the time. I can put a jar on top of the microwave which is just next to the stove and it has a nice gentle warmth there. If I need more heat I can put it on top of the simmer side lid, on a spacer perhaps, and cover with a cloth. In the summer we may not run the stove at all for days and although not cold, the house isn't that warm either - usually 12 - 15 celsius, which is on the cool side for many ferments. I wonder whether this is the reason I don't experiment very much with fermenting though - not having a reliable warm place year round.
If I had an airing cupboard (a space where a hot water tank is placed) that is usually a warm spot, but our hot water tank is just in the corner of our bedroom, and since the water is heated by the stove, not much more reliable than the kitchen. We are thinking of ways of heating the water in summer when we don't want to run the stove, so maybe this will change in my 4 dimensional house