How Much Does It Cost to Run a Hot Tub? The Math by City

Keeping a hot tub hot costs about $25 a month in electricity for the median model certified in California, at the US average price and by the formula on its energy label. In January, our estimate for the same tub runs from $20 (Miami) to $82 (Boston). That is standby only: the tub at 102°F with its cover on. Soaking time, jets and refills add to it, and we found no published test that measures how much.

Most cost guides start from an assumed number of heater hours. We started from measured data: the certified standby watts of 1,566 approved hot tubs in the California Energy Commission’s appliance database, scaled to each month’s normal temperature in 21 US cities and priced at each state’s 2026 residential electricity rate.

Start with the number on the energy label

Every portable electric spa sold in California must pass a standby test under the state’s Title 20 appliance rules. The tub is filled, held at about 102°F with the manufacturer’s specified cover on and left unused, and the total electricity it draws is reported as “normalized standby power”: watts, adjusted to a standard 37°F gap between water and air.^1,11,12 For a standard spa the limit is 3.75 × fill volume^2/3 + 40 watts, set in the approved Title 20 text.¹ Manufacturers must list each model, with the cover it was tested with, in the CEC’s Modernized Appliance Efficiency Database System (MAEDbS), which anyone can search.^2,3

The required label turns that into a yearly figure: standby watts × 8,760 hours = kilowatt-hours a year, and kWh × your rate = annual standby cost.¹ It also states what it leaves out:

does not include spa usage or extreme cold conditions.

We read all 2,229 approved listings on October 6, 2026. The 1,566 standard (non-inflatable, non-swim) spas with test data, from 54 manufacturers, have a median standby power of 188 watts at a median fill of 331 gallons; the middle 80% run 132–237 watts. The median listing uses 86% of its legal limit.

Label math for the median tub: 188 W × 8,760 h = 1,647 kWh a year, or $300 at the US residential average of 18.19¢ per kWh for January–July 2026.⁴ That figure assumes a constant 65°F outdoors (102°F minus the 37°F test gap), which no US city has all year.

What the same hot tub costs by city and month

The CEC normalizes its test by assuming heat loss rises in step with the difference between water and air temperature.¹ We applied that same scaling to each month’s normal mean air temperature (NOAA 1991–2020 normals, nearest station)⁵ and each state’s residential electricity price from the Energy Information Administration.⁴ The formula is monthly kWh = standby watts × (102°F − average air temperature) ÷ 37 × hours in the month ÷ 1,000. Extending a lab normalization to real weather is our assumption: wind, sun, rain and snow are not in it.

Range: tubs at the 10th and 90th percentile of certified standby watts (132 and 237 W). Prices are state averages.

Swap in your own numbers: your tub’s standby watts, your monthly temperature from our climate data and your price per kWh. Our heat pump vs. furnace guide uses the same EIA prices and NOAA normals for home heating, and our saltwater vs. chlorine pool guide prices a salt cell’s electricity the same way.

Cost to run a hot tub in winter

In our table, January standby costs 1.7 to 7.0 times July’s, from Seattle to Phoenix. Boston’s January air (30°F) is 21 degrees milder than Fargo’s, yet the same tub costs $82 there against $43 in Fargo, because Massachusetts power averaged 30.1¢ per kWh and North Dakota’s 12.4¢.

Unlike a pool you close for the winter, a hot tub kept running all year pays for these months too. Our estimates use average temperatures, so a cold snap costs more than the monthly figure shows, and the CEC label itself excludes extreme cold.

What changes the bill

• Size. The limit grows with volume, and so do certified watts: a median 143 W for tubs of 250 gallons or less against 236 W above 450 gallons (Table 1).
• The tub’s own efficiency. Among 251–350-gallon listings, a tub at the 90th percentile draws about 1.5 times the standby watts of one at the 10th. Compare the label or the MAEDbS listing before you buy.
• 120 V vs. 240 V. Among 251–450-gallon listings, 122 plug-in-class models (rated 110–120 V) have a median standby of 166 W at 285 gallons, and 918 models rated 199–257 V a median 194 W at 340 gallons. Per 100 gallons that is 58 W against 57 W: in this data, 120 V tubs use less standby power because they are smaller, not because of the voltage.
• Inflatable spas. California sets inflatable spas a looser limit, 7 × fill volume^2/3 watts, and a label duty cycle of 5,040 hours a year instead of 8,760.¹ The 328 approved inflatable listings with data have a median of 238 W for 259 gallons, about 95 W per 100 gallons against 57 W for standard spas.
• Your price per kWh. State averages in our table run from 12.4¢ to 33.2¢, so the same tub costs 2.7 times as much to run in California as in North Dakota before weather.

Water temperature: 100°F vs. 102°F vs. 104°F

Hot tub water temperatures should never exceed 104 degrees Fahrenheit.

CPSC’s hot tub warning also notes that 100°F is considered safe for a healthy adult. Within those limits, the setting matters because standby loss follows the water–air gap. By the same formula, keeping the median tub at 104°F instead of 102°F adds 3–8% to its yearly standby energy across our cities, and 100°F saves the same share. The percentage is largest in warm places, where the gap is small to begin with. Google’s AI answer, when we checked in October 2026, put the saving from a 1–2°F drop at roughly 10%; by the CEC formula, 2°F is worth 3–8% of standby.

Is it cheaper to keep a hot tub hot all the time?

Not by the heat balance behind the CEC test. Several top search results, and Google’s AI answer, say the opposite without showing numbers. A cooler tub loses heat more slowly, and reheating only replaces the heat that was lost, so with an electric heater a setback does not use more energy. Idaho Power’s advice matches: 102°F when in use, “a lower temperature at other times,” with keeping it near 98–100°F mainly a convenience for tubs used often.⁷ The utility also notes that a typical covered tub loses about half a degree an hour with the heater off and gains about 4 degrees an hour with it on, so plan the warm-up.⁷

Refilling and reheating

Each refill means heating a full tub from tap temperature. One British thermal unit raises one pound of water by 1°F, and 3,412 Btu equal one kWh;⁸ water weighs about 8.34 pounds a gallon at 50–60°F (USGS lists 62.4 pounds per cubic foot, and a cubic foot holds 7.48 gallons).⁹ For the median 331-gallon tub and 55°F tap water (our assumption; yours varies by place and season): 331 × 8.34 × (102 − 55) ÷ 3,412 = 38 kWh, about $7 at the US average price, if every kWh ends up in the water. A portable tub’s fill volume is in its MAEDbS listing; for a built-in spa, our pool volume calculator estimates gallons for round and rectangular shapes.

Ways to cut the cost, as the sources state them

Hot air rises, so make sure your lid is gap-free and has good insulation.

• Keep the tested cover. California requires each tub to be sold with the cover it was tested with, or an approved equivalent also tested with it.¹ A worn or different cover means the label no longer describes your tub. The often-repeated claim that about 70% of a hot tub’s heat escapes through the top had no test behind it in any source we read, so we don’t use it.
• Turn it down between uses. Idaho Power: lower the temperature when not in use, and in hot summers set it to the lowest setting or turn off the heater if the tub isn’t used regularly.⁷
• Block the wind, which Idaho Power says can cool the water while you soak, and keep filters clean: clogged ones, it says, strain the pump and reduce the heater’s efficiency.⁷
• Buy on the label. Same-size listings differ by about 1.5 times in standby watts (Table 1). Idaho Power also points to a separate, lower-wattage pump for filtering and settings that lower the heat when the tub is idle.⁷

What this estimate leaves out

Soaking time with the cover off, jets, blowers, wind, snow and time-of-use rates are not in the label test, and we found no published measurement of them, so we give no number. Water care is a separate running cost: our hot tub chemical levels guide covers sanitizer and pH, and CDC’s minimums for pools are in our ideal pool chemical levels guide.¹⁰ For how we compute climate figures, see our methodology; more hot tub guides are in the hot tubs section.