Calculator
What size heater does your sauna need?
Measure the room, add the glass, and pick a heater whose maker rates it for that volume. Most backyard barrels land between 6 and 9 kW.
Pick a heater whose maker rates it for your room's volume, after you've added an allowance for glass and stone. Most backyard barrels hold around 7 to 8 m³ and land between 6 and 9 kW. The calculator below matches your room against the ratings Homecraft and Nootka publish for their heaters, and it works in metres or feet.
Try it with your room
What size heater does your sauna need?
Room to heat
9.2 m³
326 cu ft
Heaters rated for it
7.5–9 kW
- Homecraft Revive 7.5 kW, rated by Homecraft for 7.1–10.5 m³
- Nootka 7.5 kW, rated by Nootka for 6.1–10.1 m³
- Homecraft Revive 9 kW, rated by Homecraft for 9.2–12.7 m³
- Nootka 9 kW, rated by Nootka for 7.3–12.7 m³
Ratings are each maker’s own, for an insulated room. We add 1.2 m³ for every square metre of glass, stone or tile, as Homecraft’s manual does for masonry. A solid-wood outdoor barrel isn’t insulated, so if your room sits near the top of a range, take the next size up.
The heaters Canadian makers rate by room size
Homecraft and Nootka both publish the room volume each of their heaters is made for, and that's what the calculator uses. Every rating has a floor as well as a ceiling, so a heater can be too big for a small room, not only too small for a big one.
| Heater | Rated room (m³) | Rated room (cu ft) | Breaker at 240V |
|---|---|---|---|
| Homecraft Revive Slim 5 kW | 2.8–7.1 | 100–250 | 30 A |
| Homecraft Revive Slim 6 kW | 5.7–9.2 | 200–325 | 40 A |
| Homecraft Revive 6 kW | 5.7–9.2 | 200–325 | 40 A |
| Homecraft Revive 7.5 kW | 7.1–10.5 | 250–370 | 40 A |
| Nootka 7.5 kW | 6.1–10.1 | 215–356 | 40 A |
| Homecraft Revive 9 kW | 9.2–12.7 | 325–450 | 50 A |
| Nootka 9 kW | 7.3–12.7 | 259–450 | 50 A |
| Homecraft Apex 10 kW | 11.3–17.7 | 400–625 | 50 A |
| Homecraft Apex 12 kW | 12.0–19.8 | 425–700 | 70 A |
| Homecraft Apex 15 kW | 15.6–25.5 | 550–900 | 80 A |
From Homecraft's Revive Slim, Revive and Apex pages and Nootka's heater manual, read Oct 11, 2026. Homecraft rates in cubic feet and Nootka in cubic metres; the other column is our conversion. Nootka rates its heaters for an R12-insulated room. Nootka's heater ships with its saunas and isn't sold on its own here.
Measure the inside of the room
Use the inside dimensions, wall to wall and floor to ceiling. For a cube or a cabin, you'll multiply the width by the depth by the height. A barrel's a cylinder, so multiply 3.14 by the radius squared and then by the length.
A barrel 2 m across and 2.4 m long works out to about 7.5 m³ by our math. That sits inside the ratings for Homecraft's 6 and 7.5 kW Revive and both of Nootka's heaters, which is why most barrels ship with something in that band. A small cabin with a standard ceiling usually comes out a bit bigger, and that's where the 9 kW sizes take over.
Glass and stone count as extra volume
Glass, tile and stone soak up heat that the wood would otherwise hold, so the room behaves like a bigger one than it is. Homecraft's Revive manual adds 1.2 m³ for every square metre of plastered or masonry surface, and it names glass among the surfaces that stretch the warm-up. We apply the same allowance to glass.
That adds up quickly. A full-glass door about 0.8 m wide and 2 m tall adds almost 2 m³ by that allowance, enough to push a 7.5 m³ barrel into the range where a 9 kW heater fits better. Enter your glass and stone area in the calculator and it'll do the sum for you.
Barrels aren't insulated, so lean toward the larger size
The makers' ratings assume an insulated room, and Nootka's says so in as many words. A backyard barrel is solid cedar with no insulation behind it, and in February it loses heat faster than an indoor room of the same size.
If your room lands near the top of a heater's range, we'd take the next size up. Nootka makes the same call with its own barrels. It ships the 9 kW heater as standard and offers the 7.5 kW as an option, which it says takes a few extra minutes to get hot.
A heater can be too big for the room
Every rating in the table has a minimum as well as a maximum, so stay inside the range and don't simply buy the biggest heater you can wire. For a small barrel, the Revive Slim's low floor makes it the easier fit.
Where to buy
Homecraft Saunas Heaters & Stoves
Homecraft Revive Slim
Built in British Columbia
Homecraft Saunas Heaters & Stoves
Homecraft Revive
Built in British Columbia
Homecraft Saunas Heaters & Stoves
Homecraft Apex
Built in British Columbia
Wood stoves are rated differently
Wood-stove makers give a maximum room size rather than a range, so the calculator doesn't cover them. Henki rates its bigger H2 for a larger room than its H1, and each product page gives the figure. You'll find what every Canadian stove maker states in sauna heaters and stoves made in Canada.
Where to buy
Then check the circuit
The heater you choose sets the breaker, and the table gives each one's size, so you'll want it in hand when you call an electrician. The wire, the timer and the rules on doing it yourself are all in how to wire a sauna heater, and the running-cost calculator shows what each size costs to run in your province.
How did we work this out?
We read Homecraft's Revive Slim, Revive and Apex pages and its Revive installation manual, and Nootka's heater installation guide, on Oct 11, 2026. The ratings are the makers' own, the conversions between cubic feet and cubic metres are ours, and so is the decision to count glass with masonry. For a room no rating covers, the calculator falls back to our rule of thumb of about 1 kW for every 45 cubic feet and says so.
Common questions
- What size heater does an 8 ft barrel sauna need?
- An 8 ft barrel sauna about 2 m across holds roughly 7.5 m³, by our math, which suits a 6 to 9 kW heater. Nootka ships its 8 ft barrel with a 9 kW heater as standard and offers a 7.5 kW option. Add more for a glass door.
- How many kW does a sauna heater need per cubic metre?
- Makers rate heaters by room ranges rather than a fixed figure per cubic metre. Homecraft rates its 9 kW Revive for 9.2 to 12.7 m³ (325 to 450 cu ft), and Nootka rates its 9 kW heater for 7.3 to 12.7 m³ in an insulated room.
- Does a glass door change the heater size a sauna needs?
- Yes. Homecraft's manual adds 1.2 m³ to a sauna's volume for each square metre of plastered or masonry surface, and we apply the same allowance to glass. A full-glass door about 0.8 by 2 m adds almost 2 m³.
- Can a sauna heater be too big for the room?
- Yes. Heater makers set a minimum room size as well as a maximum, such as 325 cu ft (9.2 m³) for Homecraft's 9 kW Revive. Choose a heater whose rated range includes your room's volume.
We review from makers’ documentation, owner reports and published research. How we choose products and write reviews.
