Sauna Heater Size Calculator
The wrong heater size means a sauna that never gets hot enough — or one that wastes electricity overshooting. Enter your room dimensions below and we'll match you with the right Harvia heater, the brand Grayson installs in every Saunas Plus build.
How heater sizing works
The rule of thumb is about 1 kW per 45 cubic feet of sauna space. But glass doors, windows, uninsulated walls, and high ceilings all bleed heat — so we adjust your room's effective volume upward before calculating. Harvia's own sizing charts follow the same method.
When in doubt, size up slightly. An undersized heater runs constantly and still can't hit temperature; a slightly oversized one cycles normally and lasts longer.