Sauna heater size calculator

Enter your room and this returns the kW figure Harvia's own sizing rule produces, then shows exactly what manufacturer manuals specify for breaker and wire at that size — alongside what the generic code formula gives, because the two do not agree.

Disclosure and scope. This page contains affiliate links; we may earn a commission on qualifying purchases at no cost to you. This tool reproduces published manufacturer and code figures so you can check them yourself. It is a starting point for a conversation with a licensed electrician, not an electrical specification, and it is not a substitute for your heater's own installation manual or your local inspector.

Sauna room

Length interior, feet

Width interior, feet

Ceiling height interior, feet

Wall construction

Wall type Harvia applies a 1.5× volume factor to non-insulated log rooms.

Glass area sq ft — door and windows A typical full glass door is roughly 15–18 sq ft.

Stone, tile, brick or concrete sq ft of exposed uninsulated surface

Supply voltage

Circuit voltage

Wire run length feet from panel to heater

I understand this tool reproduces published figures for reference only, that the final circuit must be sized and installed by a licensed electrician to the code edition my jurisdiction has adopted, and that my heater's installation manual governs over anything shown here.

Where these numbers come from

Nothing on this page is our own engineering determination. Every figure below is reproduced from a published source and linked so you can read it in context.

Sizing rule. Harvia, How do I select the correct heater power — one kilowatt per cubic metre of room volume; each square metre of glass, stone or similar non-insulated surface counts as an extra 1.2 m³; non-insulated log rooms take a 1.5 factor. Harvia support
Breaker and wire, 4.5–8 kW. Harvia heater installation guide: 30 A double-pole with 10/2 for 4.5 and 6 kW, 8/2 beyond 30 ft of run; 40 A with 8/2 for 8 kW; copper with 90 °C insulation; hard-wired; and the manual's own instruction not to use a GFCI. Harvia installation guide (PDF)
Breaker and wire, 9–10.5 kW, and the long-run threshold. Redwood Outdoors heater and electrical FAQ: 45 A with 8/2 at 9 kW, 50 A with 6/2 at 10.5 kW, and 8/2 for a 6 kW heater beyond 90 ft. Redwood Outdoors FAQ
Room volume bands and wire size by model. Harvia KIP series manual, model specification table. Harvia KIP manual (PDF)
Code framework. Fixed electric space-heating equipment falls under NEC Article 424; branch circuits under Article 210, including the 125% continuous-load rule and the GFCI requirements of 210.8. Adopted editions vary by jurisdiction — 2023, 2020 and 2017 are all still in force somewhere.

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