Heaters and stones: electric or wood
The heater decides how the sauna feels: fast and constant, or slow and alive. The stones decide how the steam rises when water is ladled on.
Choosing the output
Rule of thumb: 1 kW per cubic metre of cabin, plus extra for glass and bare stone walls. A cabin of 200 × 200 × 210 cm (roughly 8 m³) therefore needs a heater of 8 to 9 kW.
Electric
Wall-mounted heaters with stones on top are compact and affordable; tower heaters with plenty of stones give a softer, longer-lasting steam. Mind the connection: from 6 kW usually 400 V.
Wood
A wood-fired stove needs an approved flue, a floor plate and clearance from the timber. In return you get a sauna without electricity and a scent no electric heater can match.
The stones
Olivine diabase or volcanic stone, sorted by size: large stones at the bottom, smaller ones on top. Restack once a year and replace any broken stones.