Harvia
Harvia Hidden Heater sauna heater
Harvia makes the Hidden Heater in 3 sizes, from 6 to 12 kW, for saunas of 212 ft³ to 600 ft³. Slide to your room size to see which one fits, how fast it heats and what it needs from your fuse box.
Updated Oct 18, 2026
Output
6–12 kW
Rooms
212 ft³–600 ft³
Stones
33 lb
Sizes
3
Which size fits your sauna?
Your room's effective volume
424 ft³
Best fit: HH9
Work out your effective volumeEffective volume = inside volume, plus 1.2 m³ for every m² of glass, tile or stone; × 1.5 for solid log walls (Harvia's rule, used by most planners).
Sizes and specifications
| Model | Output | Room range | Stones | Heat-up | Per session |
|---|
Heat-up and cost are our heat model's estimate for each size in a room at the middle of its range: indoor, insulated walls, 68 °F around the sauna, heated to 176 °F, one hour of bathing, electricity at $0.18/kWh (United States average).
Electrical connection
| Model | Supply | Current | Fuse / breaker | Cable |
|---|---|---|---|---|
| Hidden Heater HH6 | 3~ 400 V | 8.7 A | – | – |
| Hidden Heater HH9 | 3~ 400 V | 13 A | – | – |
| Hidden Heater HH12 | 3~ 400 V | 17.3 A | – | – |
Current is computed from the output; fuse and cable are shown where the maker or dealer states them. A licensed electrician sizes and installs the circuit following the heater's manual and local rules.
Where to see it
- Hidden Heater HH6€1,069 at esaunashop.com (2026-10-18)
- Hidden Heater HH9€1,121 at esaunashop.com (2026-10-18)
- Hidden Heater HH12€1,172 at esaunashop.com (2026-10-18)
Prices and availability come from the shop or maker and change; their page is what counts. Shop offers are added as retailers join.
Sources
- esaunashop.com/harvia-hidden-heater-hh6-6-0-kwdealer · read 2026-10-18
- esaunashop.com/harvia-hidden-heater-hh9-9-0-kwdealer · read 2026-10-18
- esaunashop.com/harvia-hidden-heater-hh12-12-00-kwdealer · read 2026-10-18
Other heaters for the same rooms
Questions and answers
What size sauna does the Harvia Hidden Heater heat?
Harvia rates the sizes for these rooms: Hidden Heater HH6 212 ft³–353 ft³; Hidden Heater HH9 353 ft³–494 ft³; Hidden Heater HH12 424 ft³–600 ft³. Use your room's effective volume: add 1.2 m³ for every m² of glass, tile or stone, and multiply by 1.5 for solid log walls.
What fuse or breaker does the Harvia Hidden Heater need?
It depends on the size and your supply: Hidden Heater HH6: 3~ 400 V: 8.7 A; Hidden Heater HH9: 3~ 400 V: 13 A; Hidden Heater HH12: 3~ 400 V: 17.3 A. A licensed electrician sizes the circuit from the heater's manual and local rules.
How long does the Harvia Hidden Heater take to heat up?
In a well-insulated indoor room at the middle of each size's range, our heat model gives: Hidden Heater HH6 25–35 min; Hidden Heater HH9 20–25 min; Hidden Heater HH12 15–20 min to reach 176 °F. Outdoor saunas, glass and cold weather take longer.
How many stones does the Harvia Hidden Heater take?
As stated by Harvia: Hidden Heater HH6 33 lb; Hidden Heater HH9 33 lb; Hidden Heater HH12 33 lb. Use the stone size the manual specifies and re-stack the stones at least once a year, replacing crumbled ones.