A recommendation you can check
The Harvia, HUUM and US retailer rules run on your room. The answer is the middle of the three, so no single rule decides.
Brand-neutral sauna heater sizing · Made in Finland
The right heater for your sauna, without the sales pitch
Every heater maker has its own sizing rule, and their calculators exist to sell you their heater. Löyly Sizer runs all the common rules on your room, shows where they disagree, and lists heaters from eleven brands that are actually rated for it.
- Three sizing rules side by side
- 48 heaters, 11 brands
- Every figure linked to its source
The problem
Three calculators, three answers
Heater makers agree on the starting point, about 1 kW per cubic metre, but not on how much extra to add for glass, stone and thin walls. For a typical backyard barrel sauna, the rules can disagree by a factor of two or more, which is the difference between a heater that cycles harshly and one that takes forever to heat.
What you get
Everything you need to choose, in one place
How long it takes to heat
A heat model estimates warm-up time for the recommended size and one size either side, so you can see what an extra step of power buys.
Heaters rated for your room
Models from Harvia, HUUM, Helo, Tylö, Tulikivi, Saunum, Finlandia, Amerec, Kastor, IKI and Narvi, listed by fit, not by commission.
Circuit and running cost
Current at 240 V, 230 V and 400 V, a typical breaker size, and what a session costs at your electricity price.
What else you need
Pick a heater and see exactly how many stones it takes, plus the few accessories that are actually worth buying.
Wood, infrared and heat-storing
Wood stoves sized by room volume, infrared by number of people, and the Finnish heat-storing stoves that give löyly for hours.
Learn
Sauna knowledge from Finland
Short, sourced guides on what makes a sauna good, from the law of löyly to ventilation. Written in plain English for people building or buying their first sauna.
What makes a good sauna→The law of löyly, bench and ceiling heights, ventilation, with a bench height checker.Why heater calculators disagree→How Harvia, HUUM and US retailers count glass, masonry and log walls.Barrel sauna heater size→Why thin staves need more power, with sizes and warm-up times.Wood-burning stove size→Sizing a wood stove by room volume, with rated ranges.Sauna accessories worth buying→What you need, what is worth having, and how many stones your heater takes.Smoke saunas and heat-storing stoves→The traditional Finnish favourites: how they work and what it takes to have one.
Why trust it
Built by a sauna owner, not a heater shop
Brand-neutral
Heaters appear because their rated range fits your room. The order never depends on commission.
Sourced
Sizing rules, heater ranges and research link to the manufacturer, study or guide they came from.
Private
The calculator runs in your browser. Nothing you enter is sent anywhere.
Honest about money
Some links may earn a commission. That keeps the site free, and it is disclosed wherever it applies.
Ready to size your sauna?
Takes about a minute. Change any number and the results update.