Sauna heater guide: electric, wood-fired, infrared

The heater is the heart of a traditional sauna: it warms the air, heats the stones, and turns a splash of water into steam. Infrared saunas work differently, using radiant emitters instead of a rock heater, which is why the two feel so different. This guide walks through the main heater types, how to size one in kilowatts, and what to plan for on wiring, stones, controls, and safety.

The short answer

For most home saunas, an electric heater sized to the room volume is the practical default: it heats on a timer, needs little upkeep, and pairs with simple or app-based controls. Choose wood-fired if you want authentic radiant heat and off-grid use and don’t mind the extra work. If you’re leaning toward infrared, you’re really choosing a different category of sauna, not just a different heater, so it’s worth reading our infrared vs traditional comparison before you commit.

Heater types compared

There are four main ways to heat a sauna. The first three heat a real cabin with stones; infrared is a separate approach.

Electric is the most common choice because it is clean, quiet, and easy to schedule. Wood-fired wins on atmosphere and independence from the grid, which is why it’s popular for outdoor and barrel saunas. Gas is a niche option used where electrical supply is limited but gas is available. Infrared isn’t a rock heater at all, so if you want loyly (the burst of steam from water on hot stones) it isn’t the right route.

Sizing your heater in kilowatts

This is the section that matters most for getting the experience right. Sauna heaters are rated in kilowatts (kW), and the rating is matched to the volume of the room, not the floor area.

The widely used rule of thumb is roughly 1 kW for every 1.3 cubic metres (about 45 cubic feet) of cabin volume. To estimate volume, multiply length by width by height in metres.

1. Measure the room: for example, 2 m long x 2 m wide x 2.1 m high.
2. Multiply to get volume: 2 x 2 x 2.1 = 8.4 cubic metres.
3. Divide by 1.3: 8.4 / 1.3 = about 6.5 kW, so a 6 to 6.5 kW heater is a sensible starting point.

Then adjust upward for anything that loses heat:

Manufacturers publish a sizing chart for each model listing the minimum and maximum cabin volume it suits. Use the chart as the final word, and if you fall between sizes, choose the larger one so the heater isn’t running flat-out. For help working out cabin dimensions in the first place, see our guide to sauna dimensions.

Electrical requirements

Power draw rises with heater size, and that drives the wiring.

• Small heaters (roughly under 3 kW) can sometimes run on a standard household circuit, which is why some compact plug-in models exist.
• Most sauna-room heaters (around 4.5 to 9 kW) need a dedicated 240V circuit with a correctly rated breaker and cable gauge.
• The exact breaker and wire size depend on the heater’s wattage and your local electrical code.

Treat these as general rules of thumb only. Confirm the circuit, breaker, and wiring with the manufacturer’s spec sheet and a licensed electrician before you buy. Getting this wrong is both a fire risk and a reason a heater fails early.

Sauna stones and steam

Rock heaters (electric, wood, and gas) sit under a bed of sauna stones, and those stones do real work:

• Thermal mass: they hold heat and even out the cabin temperature, so it doesn’t swing every time the element cycles.
• Loyly: when you ladle water over hot stones, it flashes to steam, lifting the humidity and the feeling of heat without raising the air temperature much. That moist heat is a big part of why a traditional sauna feels the way it does, which we cover in how hot a sauna should be.

A few practical points on stones:

• Choose dense, heat-resistant stones (peridotite, olivine, and similar) made for saunas, not random landscaping rocks, which can crack or even shatter.
• Arrange them loosely so air and heat can move between them. Don’t pack them tightly or bury the elements.
• Replace them when they crack, crumble, or wear smooth, typically every year or two with regular use. Inspect and restack once or twice a year.

Controls and convenience

How you run the heater shapes daily use as much as how it heats:

• Built-in controls sit on the heater itself, a simple knob-and-thermostat setup that’s reliable and cheap.
• External controls mount on the wall outside the hot cabin, which is more comfortable to reach and easier to read.
• Timers let you set a heat-up window so the sauna is ready when you are; many include a safety cut-off after a set number of hours.
• Wi-Fi and app control let you start the heater from your phone, so it’s warm by the time you walk out to it. This is electric-only and worth having if you use the sauna often.

Wood-fired specifics

Wood-fired heaters reward you with ambiance but ask for more in return:

• Chimney and flue: you need a proper insulated flue, correctly routed through the wall or roof, with the right cap and clearances.
• Clearances to combustibles: wood stoves run hot, so they need generous distances from walls and benches, often larger than electric units. Heat shields can reduce these, but follow the manufacturer’s figures.
• Fuel and tending: keep dry, seasoned wood on hand, expect a longer warm-up, and plan to feed the fire during a session.
• Never leave a wood-fired heater unattended while it’s burning, and let ashes cool fully before disposal.

Cost and running cost

Heater price is only part of the picture. Wood-fired units can cost more up front once you add the flue kit, while electric heaters add the price of the dedicated circuit and any electrician’s labour. Running cost then depends on local energy or fuel prices and how often you heat up. For a fuller breakdown of build and ownership costs, see our sauna cost guide.

Safety essentials

A few non-negotiables apply to every rock heater:

• Respect clearances to combustibles. Keep walls, benches, and anything flammable the manufacturer-specified distance from the heater.
• Fit a guard rail around the heater so no one brushes the hot surface or stones by accident.
• Ensure proper ventilation. Good airflow keeps the cabin safe and the steam quality good; follow the heater’s intake and exhaust guidance.
• Use professional installation for electrical connections (licensed electrician) and for wood-fired flues (qualified installer), and follow local codes throughout.

The bottom line

Pick the heater type that matches how you want to use the sauna, then size it to your cabin volume and let the manufacturer’s chart and a licensed electrician confirm the details. Get the type and the kW right and almost everything else, from steam to running cost, falls into place. If you’d rather buy a sauna with a properly matched heater already fitted, start with our roundup of the best barrel saunas.