Sauna heater size calculator
Enter the inside dimensions. The planner adjusts the volume for solid-wood walls and glass, picks a 240 V heater size from a published spec table, and adds up running and setup costs.
1 · The room
Saunacraft: "Recommend height is 7'. Max. height should never be higher than 8'."
Check your kit's spec sheet for an insulation layer. Harvia counts log walls at 1.5× volume; we apply the same to solid barrel staves, which no maker states for barrels — check the heater your barrel maker pairs with it.
A glass door of about 2 × 6 ft is 12 sq ft. Each uninsulated square meter adds 1 m³ of volume (HUUM manual).
2 · Use
3 · Setup
Heater size (Saunacraft table)
– kW
| Room volume | |
|---|---|
| Volume for heater sizing | |
| Harvia average (1 kW/m³) | |
| Current at 240 V | |
| Breaker / wire (Saunacraft) | |
| Heat-up time | |
| Electricity, per month (max) |
Setup cost
| Kit (your quote) | |
|---|---|
| Foundation | |
| 240 V circuit | |
| Total |
Not in the total: permits, delivery and assembly labor, and possibly trenching for a long outdoor run or a panel upgrade — Fixr's circuit price describes a circuit in the home's existing panel and doesn't say what it covers beyond that. Ask for local quotes.
Breaker and wire sizes are Saunacraft's recommendation for its own heaters; other makers list different sizes for the same kW (Almost Heaven's 6 kW heater: 30 A breaker, 10/2 wire). Your electrician works from the manual of the heater you buy and pulls the permit.
Installed price by size (Fixr)
| Capacity | Installed price (U.S.) |
|---|---|
| 1 people | $2,000 – $3,500 |
| 2–4 people | $3,000 – $6,000 |
| 5–7 people | $6,000 – $9,000 |
| 8–10 people | $9,000 – $10,000 |
Source: Fixr, Sauna installation cost (updated Jan 31, 2025). A prefab 4-person kit you assemble yourself: $2,640 – $4,790.
The heater table we match against
| kW | Room, cu ft | Amps @ 240 V | Breaker | Wire (AWG) | Mount |
|---|---|---|---|---|---|
| 4 | 100–150 | 16.7 | 30 A | 10 | wall |
| 5 | 150–250 | 20.8 | 30 A | 10 | wall |
| 6 | 200–300 | 25 | 40 A | 8 | wall |
| 7.5 | 290–375 | 31.3 | 40 A | 8 | wall |
| 9 | 360–450 | 37.5 | 50 A | 8 | wall |
| 12 | 450–700 | 50 | 60 A | 6 | floor |
| 15 | 600–900 | 62.5 | 80 A | 4 | floor |
Saunacraft 240 V single-phase models. Other brands publish their own ranges, so check the spec of the heater you actually buy.
How the planner works
- Volume: barrel = π × (diameter ÷ 2)² × length; cabin and cube = length × width × height (inside dimensions).
- Solid log walls without insulation: volume × 1.5 (Harvia); we use the same factor for solid barrel staves (our assumption). Glass, brick or tile: + 1 m³ per m² (≈ 3.3 cu ft per sq ft, HUUM).
- Heater: the smallest 240 V Saunacraft model whose range covers the sizing volume at no more than 90% of its maximum. Harvia's 1 kW per m³ average is shown as a second opinion — in our checks it comes out higher.
- Electricity: heater kW × (heat-up + session time) × sessions per month × your rate. That assumes the heater runs at full power the whole time, so it is a ceiling; the thermostat switches it off once the room is hot.
- Setup: your kit price + pad area × $4–$8 per sq ft for concrete or $1.25–$1.80 for a gravel pad (This Old House) + $500–$800 for a new circuit (Fixr).
Not modelled: outdoor winter temperatures (we found no manufacturer figure for a cold-climate allowance), wood-burning stoves, and infrared cabins.
Sources
- SaunaFin, Saunacraft Heater Specifications table, 240V single phase, in the "TPT3 & EL-13 (208 Volt-3 Phase)" document (Oct 2024), p. 3 — 240 V heater table: room range (cu ft), amps, wire, breaker; "Recommend targeting 90% of capacity"; ceiling 7 ft, never above 8 ft
- Harvia, Electric heaters (harvia.com) — average 1 kW per cubic meter of room volume
- HUUM DROP electric sauna heater manual, EU edition (H1001L02 v6, 2025), p. 4, Table 1 note — add 1 m³ per m² of uninsulated glass, brick or tile wall; heat-up "around one hour"
- Harvia, The Wall USA Owner's/Operator's Manual (Y05-0859), p. 7 — log walls: multiply room volume by 1.5
- Almost Heaven Saunas, Wall heater installation & owner's manual (Harvia heater) — heat-up to 175–185°F in about 45–60 minutes "properly installed"
- Almost Heaven Saunas, FAQ (checked Nov 1, 2026) — outdoors "in the middle of winter, give your sauna a little more time to heat up"
- U.S. EIA, Electric Power Monthly, Table 5.6.A (average retail price, residential) — U.S. residential average 18.16¢/kWh (August 2026, U.S. residential average (preliminary; next EIA release Nov 24, 2026))
- Fixr, Sauna installation cost (updated Jan 31, 2025) — "220-volt circuit" in the existing panel + "220-volt receptacle" $500–$800 (Fixr's wording); installed price by size; DIY prefab 4-person kit $2,640–$4,790; electric sauna $25–$30/month to run
- This Old House, Concrete slab cost (updated Mar 17, 2026) — concrete slab $4–$8 per sq ft (example: a 30 × 30 ft slab)
- This Old House, How To Build a Shed Foundation (updated May 28, 2026) — gravel pad $1.25–$1.80 per sq ft (shed foundations)
Figures checked 2026-11-01.
Safety and permits
A sauna heater needs its own circuit sized to the maker's manual — have a licensed electrician wire it and pull the permit. Wood-burning stoves need the clearances and chimney in the stove's manual and local code approval. Before digging for a foundation, call 811. This site doesn't give medical advice: if you're pregnant or have a health condition, ask your doctor before using a sauna.