Two numbers decide your heater: your room's volume in cubic feet, and what your electrical panel can spare. Here's how to get both in about five minutes.
Step 1 — Measure the room
Length × width × height, in feet. A 6' × 7' sauna with a 7' ceiling is 294 cubic feet. That's the only math you need.
Step 2 — Apply the rule
Plan on 1 kW of heater for every 45–50 cubic feet of room. For our 294-cubic-foot example: 294 ÷ 45 ≈ 6.5 kW — so an 8 kW heater with a little headroom, not a 6 kW running flat-out.
Step 3 — Adjust for glass and cold walls
- Add about 1 kW for a full glass door or a glass wall panel — glass sheds heat.
- Outdoor sauna, or any uninsulated wall? Add 25% to your total.
- Landed between two sizes? Size up. An oversized heater cycles gently; an undersized one never quite gets there and wears itself out trying.
Step 4 — Check the electrical before you order
Every electric sauna heater we sell is 240 V, hardwired on its own dedicated circuit, installed by a licensed electrician. What that means at the panel:
- 6 kW — 25 A draw · 30 A breaker · 10 AWG copper
- 8 kW — 33 A draw · 40 A breaker · 8 AWG copper
- 9 kW — 38 A draw · 50 A breaker · 6 AWG copper
- Wood-burning — no electrical at all; you'll need a 6" insulated chimney run and proper clearances instead
If your panel is already full, that's not a dead end — it's a conversation for your electrician about a subpanel, or a reason to look at a wood-fired stove.
Don't forget the stones
Heaters ship without stones, and the stone mass is half the experience. Wall-mount heaters take roughly one 40 lb set; tower heaters hold 200 lb or more (4–6 sets). More stone = softer, longer steam.
The shortcut
Skip the spreadsheet: every heater order includes a pre-ship call where we confirm your room volume, glass, insulation and panel capacity before anything ships. If we sized it wrong, that's on us. Shop sauna heaters → or start a free room design →.