Sauna or hot tub — which costs more to run?

Updated September 20, 2026

People assume the sauna is the expensive one. It has the bigger heater, after all — 6 kW against 4 kW. In practice it is usually the cheaper of the two, and often by a wide margin.

The short answer

At $0.17/kWh, roughly:

The hot tub costs more despite the smaller heater. The reason is simple.

It is about hours, not kilowatts

A sauna heater runs when you use it. Three sessions a week at roughly 80 minutes each is about four hours of running time, and for most of that the heater is cycling rather than drawing full power.

A hot tub is heated every hour of every day, whether anyone gets in or not. Keeping 400 gallons at 100 °F through a winter night is a small load running constantly, and constant beats large.

So the comparison is a big heater used occasionally against a small one that never stops.

What moves each number

For the sauna, it is how often you heat it. Each heat-up from cold is the expensive part; a longer sit is nearly free. Two people going one after the other costs far less than heating twice.

For the hot tub, it is barely about use at all. It is the cover, the setpoint, and the weather. Whether you soak nightly or twice a month changes the bill much less than people expect.

That difference matters if you are choosing between them. A sauna’s cost scales with how much you use it. A hot tub’s is mostly fixed the day you fill it.

Which suits you

A sauna if you will use it in bursts, want low standing cost, or would resent paying for something sitting idle. Cheaper to run, cheaper to leave alone for a month.

A hot tub if you want something always ready with no wait. That readiness is exactly what you are paying for — the cost is the price of it being hot at 10pm on a Tuesday without planning.

Run your own numbers: the sauna cost calculator and the hot tub cost calculator both take your electricity rate rather than a national average, which is the figure that actually decides this.