Is there an energy efficient type of Sauna yet? It seems a huge waste of energy to heat a room to such high temperatures, using it for maybe an hour and then let it all puff away.
The rooms are small though. Is it a waste of energy to heat an entire oven to bake a cake, only to let the heat all puff away? It would only be a waste if you heated the sauna, but then didn't use it.
It is! That's why the Omnia/Pardini oven is so much more energy-efficient.
I remember heating a small sauna at a friends' house with wood (something like 3 square meters), you don't need much if the sauna is reasonably isolated to the outside.
Place the sauna in the basement. Heat goes up on its own.