How we verify
Sauna shopping is full of confidently stated numbers that nobody published. We would rather show you a gap than fill it, so here is exactly how the figures on this site are sourced.
1.Every spec has a source and a date
Each record carries the URL it was read from and the day it was read. Specs for one product often come from several places, because the price sits on a retailer page while the sizing table sits with the heater maker. So records carry several sources, and each figure says which one it came from.
2.A shop's number and a maker's number are not the same number
Specialist sauna retailers publish dimensions and capacities that some manufacturers make hard to find, and that data is genuinely useful, so we carry it and label it retailer-published. But a maker's own sizing table is what our calculator matches against. Where both exist, the maker wins.
3.Empty beats guessed
A dash means the publisher does not state that figure. It never means we could not be bothered. Right now 0 of the 11 heaters we track have no published room volume rating we could find, and the calculator tells you it did not evaluate them rather than quietly guessing.
4.Heater sizing follows the maker's own tables
A heater matches your sauna when your room's effective volume falls inside that heater's own published minimum to maximum range. We never apply a generic formula over the top of a maker's table, and we sort matches toward the middle of each range because Harvia advises against buying at the edges.
5.Electrical figures are arithmetic, not instructions
Amps shown on this site are computed from the heater's stated kW at 240 volts, with a conservative continuous-load margin that we mark as ours. None of it is installation guidance. A licensed electrician should confirm the circuit, breaker and wiring for any heater, and local code on wood stoves and chimneys varies enough that checking before you buy is part of the purchase.
6.Buy links go where you can actually buy
Every buy button lands on a page where the product can be purchased or a quote requested. Where a maker sells only through dealers and no stocking retailer lists the product, we say so and show no button at all.
The sizing standards we compute with
These are the exact rules the heater calculator applies, rendered from the same code that does the arithmetic.
Manufacturer rules we apply
Base power per volume: 1 kW per m3 of hot-room volume
Harvia publishes 1 kW per cubic meter as the average requirement, and notes the calculated figure is in most cases the minimum. An undersized heater runs longer and harder, which shortens its life.
Read from Harvia's published guidance on 2026-08-30.
Glass and non-insulated surface: +1.2 m3 of effective volume per m2
Harvia treats each square meter of glass, stone or similar non-insulated surface as if the room were 1.2 cubic meters larger, because those surfaces store and leak heat.
Read from Harvia's published guidance on 2026-08-30.
Non-insulated log walls: multiply room volume by 1.5
Harvia applies a 1.5 factor when the hot-room interior walls are non-insulated logs.
Read from Harvia's published guidance on 2026-08-30.
Where in a heater’s range to buy: aim for the middle of the maker’s min-max m3 range
Harvia advises against buying at the minimum or maximum of a heater’s stated volume range. We sort matches by distance from the midpoint of each heater’s own range for this reason.
Read from Harvia's published guidance on 2026-08-30.
Framing that is ours
Circuit sizing framing: amps at 240 V, then 125% for a continuous load
This is our conservative framing, not an installation instruction. A sauna heater runs for hours, and sizing a circuit at 125% of a continuous load is common North American practice. Every figure we show is paired with the same advice: have a licensed electrician confirm the circuit, breaker and wiring for your installation.
We track 15 saunas and 11 heaters. The oldest verification date on any record is 2026-08-30. Who runs this site and why is on the about page.