Sauna heater size calculator

Too small a heater and the room never gets properly hot. Too big and you're paying for power you don't need. Type in your room's size and this gives you a rough heater size, using the sizing rules the heater maker Harvia publishes.

Units
–

A rough guide only. Always check the room size range the maker gives for the heater you're looking at, and follow its installation manual. Most electric sauna heaters are hard-wired, and that work needs a licensed electrician. It isn't a DIY job.

How the sum works

  1. Room volume. Length × width × height.
  2. Glass and stone add to it. Surfaces that aren't insulated soak up heat. Harvia's manuals say to add 1.2 cubic metres of volume for each square metre of glass, brick or tile.
  3. Log walls add more. For a room with solid log walls, the same manuals multiply the volume by 1.5.
  4. About 1 kW per cubic metre. Harvia's heater catalogue works on roughly one kilowatt of heater for each cubic metre of that adjusted volume.

That's why a sauna with a big glass front can need a noticeably bigger heater than a plain room of the same size.

Sources