An inflatable hot tub is cheap to buy, but it’s warm water in a thin-walled bag, and the heater has to keep replacing what leaks out. Insulation and the cover decide how often it runs.
This article covers how to estimate and cut the running cost. For the rest of the hot tub decisions, start with the hot tub buying guide.
Short answer: every degree the water loses costs money to put back. Buy for insulation and a good cover, and use the formula below to estimate your bill.
The formula
The EIA defines one Btu as the heat to warm one pound of water by 1°F, and one kWh as 3,412 Btu. Water weighs about 8.34 lbs per gallon (USGS).
So for any tub: kWh = gallons × 8.34 × degrees lost ÷ 3,412.
A worked example
Take a 177-gallon inflatable, like the Bestway SaluSpa Hot Springs or Coleman SaluSpa 4-Person.
| Heat the heater replaces per day | kWh per day | Cost per day at 18.34¢ | Cost per 30 days |
|---|---|---|---|
| 5°F | about 2.2 | about 40¢ | about $12 |
| 10°F | about 4.3 | about 79¢ | about $24 |
| 20°F | about 8.7 | about $1.59 | about $48 |
These are illustrations from the formula, not measurements of any tub. Pumps and bubblers add to them.
Here’s what the spec sheet won’t tell you: the daily heat loss is the number that matters, and no listing publishes it. It depends on the walls, the cover, wind, and the air temperature.
What helps
- Insulated walls and floor. Bestway claims its EnergySense insulation is up to 40% more efficient than typical inflatables.
- A sealed cover. Keep it on whenever you’re not in the tub.
- Wind shelter. A fence or screen cuts heat loss.
- A ground mat. It slows heat loss into the ground.
- Lower the setpoint when you’re away for days.
Run the numbers per degree
The formula gives a handy single figure for a 177-gallon tub. Each degree Fahrenheit the water loses costs about 0.43 kWh to put back (177 x 8.34 ÷ 3,412). At 18.34 cents per kWh, that is about 8 cents a degree.
So if your tub drops 6°F overnight with the cover on, that night cost you about 48 cents. You can measure this yourself: note the water temperature when you switch the heater off at night and again in the morning.
The first heat
Filling from the hose at 60°F and heating to 102°F is a 42°F rise. That takes about 18.2 kWh, or about $3.34. It is a one-time cost per fill, and small next to what holding the temperature costs over a month.
Run the numbers against the purchase price
Take the middle row of the table: 10°F a day, about $24 a month.
- Over a 6-month season, that is about $144.
- Over a full year, about $290.
The Bestway SaluSpa Hot Springs costs $455. At 10°F a day, a year and a half of electricity matches what the tub cost. At 20°F a day, it takes about nine and a half months.
These are illustrations from the formula. The lesson holds whatever your real figure is: with an inflatable, the running cost is the larger part of ownership, and the cover is the cheapest way to reduce it.
When to switch it off
If you use the tub every day or two, holding the temperature is usually simpler than reheating. If you’ll be away for a week, turn it down or off. Reheating 177 gallons by 20°F costs about $1.59, which is less than a week of holding heat at even 5°F a day.
The Coleman SaluSpa isn’t rated for use below 40°F. In a cold climate, plan a shorter season, and drain and store the tub for winter.
Climate
Cold air means more heat to replace. Coleman says its SaluSpa 4-Person can’t be used below 40°F at all.
My rule of thumb: track your electricity bill for the first month. If it’s well above the formula, look for cover leaks first.
To compare an inflatable with insulated acrylic spas, see our hot tub comparison.
Bottom line: the formula is simple; the heat loss is the unknown. Insulation and the cover are where you control it.
Sources
- U.S. Energy Information Administration, “British thermal units (Btu),” accessed October 5, 2026: eia.gov
- U.S. Energy Information Administration, Electric Power Monthly, Table 5.6.A (residential average 18.34¢/kWh, June 2026 data), accessed October 1, 2026
- U.S. Geological Survey, “Water Density,” accessed October 2, 2026: usgs.gov
- Bestway SaluSpa Hot Springs AirJet and Coleman SaluSpa 4-Person listings (capacity, EnergySense claim, temperature limits), checked September 2026
- U.S. Geological Survey, “Water Density” (a gallon of water weighs about 8.34 lbs), accessed October 2, 2026: usgs.gov