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A hot tub is a well-insulated tank of hot water that sits outside all year. The electricity it uses has almost nothing to do with how often you get in, and almost everything to do with how well it holds heat when you do not.
Key figures
- 250 watts Example: continuous heat-loss power draw
- 6 kilowatt-hours Example: daily electricity from that standby draw
- 18 cents Example: electricity cost per kWh
Find the standby number
California has required an energy label on portable electric spas since 1 June 2019, under its appliance efficiency rules. The label reports the tested standby performance of that model, measured with its cover.
If a model is sold in California, that figure exists. It is the closest thing to an honest prediction of what the tub will cost you, and it is far better than a salesperson’s “about a dollar a day”.
To turn watts into money:
standby watts x 24 / 1,000 x days x your rate per kilowatt-hour
A tub drawing 250 watts continuously uses about 6 kilowatt-hours a day. At 18 cents a kilowatt-hour that is a bit over a dollar a day, every day, before you use it at all.
The four things that change the total
- The cover. It does most of the insulating. Covers absorb water over years, get heavy, and lose their R-value. Lifting a cover that has become noticeably heavier than it was is a sign to replace it.
- The set temperature. The loss is driven by the gap between the water and the air, so every degree costs more than the last. The CPSC’s long-standing guidance is that hot tub water should never exceed 104°F, and a healthy adult is fine at around 100°F.
- The climate and the season. A tub in a windy, freezing yard in February costs several times what the same tub costs in June.
- Where it sits. Out of the wind, on an insulated base, with the cover closing properly, beats an exposed corner every time.
Letting a tub go cold and reheating it costs roughly what holding it would have cost, and in freezing weather it risks damage to plumbing. Lower the set temperature instead if you will be away for a week.
The chemical line
Hot water, small volume and a heavy bather load make a hot tub much harder on sanitiser than a pool. The CDC recommends a free chlorine concentration of at least 3 ppm in hot tubs, against at least 1 ppm in pools, and advises against using cyanuric acid stabiliser in hot tubs at all.
That means more chemical, more often, and testing before each use rather than weekly. It is a modest cost and a large part of whether the tub is pleasant.
The lines people forget
- Filters, which need rinsing regularly and replacing periodically.
- Water changes, typically every few months, which is a tank of water and a new balance each time.
- Repairs. Pumps, heaters and control boards fail eventually, and a tub outside in a cold climate works harder than one in a mild one.
Related reading: A Hot Tub Cover Purchase Needs Fit and Safe Handling and Heating a Pool Is Where the Money Goes.
Questions people ask
How much does a hot tub cost to run per month?
Multiply the standby watts from the model's energy label by 24 hours, divide by 1,000 and multiply by your electricity rate and the number of days. That is far more reliable than any general figure.
Should I turn my hot tub off when I am not using it?
Usually no. Reheating consumes roughly what holding costs, and in freezing weather an unheated tub risks damage. Lowering the set temperature is the better move.
What temperature should a hot tub be?
The CPSC advises that water temperature should never exceed 104°F, and notes that about 100°F is comfortable for a healthy adult. Children and pregnant women need extra caution.
Why does a hot tub need more chlorine than a pool?
Hot water and a small volume with many bathers consume sanitiser quickly. The CDC recommends at least 3 ppm free chlorine in hot tubs, against at least 1 ppm in pools.
Where these figures come from
- Portable Electric Spas, appliance efficiency program California Energy Commission · energy.ca.gov
- Home Pool and Hot Tub Water Treatment and Testing Centers for Disease Control and Prevention · cdc.gov
- CPSC Issues Warning for Pools, Spas, and Hot Tubs US Consumer Product Safety Commission · cpsc.gov
Figures last checked September 2026.
