Narvi
Narvi Ultra Big sauna heater
Narvi makes the Ultra Big in 3 sizes, from 18 to 30 kW, for saunas of 530 ft³ to 1,413 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
18–30 kW
Rooms
530 ft³–1,413 ft³
Stones
265 lb
Sizes
3
Which size fits your sauna?
Your room's effective volume
918 ft³
Best fit: 24 kW
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 |
|---|---|---|---|---|---|
| Ultra Big 18 kW | 18 kW | 530 ft³–848 ft³ | 265 lb | 30–40 min | $2.69 |
| Ultra Big 24 kW | 24 kW | 706 ft³–1,130 ft³ | 265 lb | 20–30 min | $3.16 |
| Ultra Big 30 kW | 30 kW | 918 ft³–1,413 ft³ | 265 lb | 20–25 min | $3.73 |
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
| Output | three-phase 400 V (per phase) | single-phase 230 V |
|---|---|---|
| 18 kW | 26 A | 78.3 A |
| 24 kW | 34.6 A | 104.3 A |
| 30 kW | 43.3 A | 130.4 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
Prices and availability come from the shop or maker and change; their page is what counts. Shop offers are added as retailers join.
Sources
- narvi.fi/en/product/narvi-ultra-big/maker · read 2026-10-18
Other heaters for the same rooms
Questions and answers
What size sauna does the Narvi Ultra Big heat?
Narvi rates the sizes for these rooms: Ultra Big 18 kW 530 ft³–848 ft³; Ultra Big 24 kW 706 ft³–1,130 ft³; Ultra Big 30 kW 918 ft³–1,413 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 Narvi Ultra Big need?
It depends on the size and your supply: Ultra Big 18 kW: 3~ 400 V: 26 A, 1~ 230 V: 78.3 A; Ultra Big 24 kW: 3~ 400 V: 34.6 A, 1~ 230 V: 104.3 A; Ultra Big 30 kW: 3~ 400 V: 43.3 A, 1~ 230 V: 130.4 A. A licensed electrician sizes the circuit from the heater's manual and local rules.
How long does the Narvi Ultra Big take to heat up?
In a well-insulated indoor room at the middle of each size's range, our heat model gives: Ultra Big 18 kW 30–40 min; Ultra Big 24 kW 20–30 min; Ultra Big 30 kW 20–25 min to reach 176 °F. Outdoor saunas, glass and cold weather take longer.
How many stones does the Narvi Ultra Big take?
As stated by Narvi: Ultra Big 18 kW 265 lb; Ultra Big 24 kW 265 lb; Ultra Big 30 kW 265 lb. Use the stone size the manual specifies and re-stack the stones at least once a year, replacing crumbled ones.