How Much Does It Cost to Run a Hot Tub?
Most of a hot tub's electric bill isn't the time you spend in it. It's the hours in between, when the heater keeps 300 gallons of water at 102°F under a cover while the air around it is 40 or 50 degrees colder. California's analysis put that "holding temperature" energy at about three-quarters of what a typical spa uses. So the two numbers that decide your bill are how well the tub holds heat, and how cold it is outside.
Since 2019, California has capped how much power a portable spa may draw while holding temperature, and published the formula. That gives a defensible baseline for any tub size: a well-covered spa built to the standard. At 18¢/kWh with normal use:
| Average outdoor temp | Inflatable, 250 gal | Hard-shell, 300 gal | Hard-shell, 450 gal |
|---|---|---|---|
| 75°F (summer) | ~$31/mo | ~$23/mo | ~$29/mo |
| 60°F (spring / fall) | ~$48/mo | ~$36/mo | ~$45/mo |
| 40°F (mild winter) | ~$71/mo | ~$53/mo | ~$66/mo |
| 20°F (cold winter) | ~$94/mo | ~$70/mo | ~$88/mo |
Two things stand out. First, a winter month can cost three times a summer month for the same tub, because the heat loss tracks the gap between the water and the air — 27 degrees in July, 82 degrees in a 20°F January. Annual cost is best estimated month by month rather than from one average.
Second, the inflatable is not the cheap one to run. The standard lets an inflatable spa lose almost twice as much heat per gallon as a hard-shell spa, which reflects what thin vinyl walls actually do. A 250-gallon inflatable built right up to its limit uses about as much electricity as a 450-gallon hard-shell tub, and about a third more than a 300-gallon one. Inflatables are cheaper to buy, not cheaper to keep hot — and budget models sold outside California don't have to meet the standard at all.
Treat these as a floor rather than a ceiling. They assume a dry, tight-fitting cover and a sheltered spot. A waterlogged cover, a gap at the hinge, or a windy deck all raise heat loss beyond what the standard's test allows.
What Affects Hot Tub Running Cost
- Cover quality: A thick, well-fitting, waterlogged-free cover is the single biggest factor in heater duty cycle. A worn-out, waterlogged or ill-fitting cover lets heat escape far faster than the standard's test allows.
- Set temperature: Each degree above 100°F (38°C) meaningfully increases heater runtime. Dropping the set point 2-4°F when not in use saves noticeably over a month.
- Ambient temperature and wind: Cold, windy locations force the heater to run far more often than sheltered, mild-climate placements.
- Pump run schedule: Some spas run the filtration pump continuously; others cycle it a few hours a day. Continuous pump operation adds a steady baseline cost even when the heater isn't active.
- Insulation quality: Full-foam insulated built-in spas retain heat far better than partially insulated or inflatable models, cutting heater duty cycle substantially.
Tips to Lower Hot Tub Running Cost
- Use a high-quality, well-fitting cover every time the tub isn't in use — this is the highest-impact change you can make.
- Add a thermal blanket (a floating layer under the cover) for inflatable hot tubs, which lose heat fastest through their thin walls.
- Lower the set temperature slightly during periods of lower use, and raise it an hour or two before you plan to use the tub.
- Shelter the tub from wind with a windbreak, gazebo, or enclosure — wind chill significantly increases heat loss on exposed spas.
- Run the pump on a schedule rather than continuously if your model allows it, and check manufacturer guidance for minimum filtration needs.
- Consider running during off-peak hours if your utility offers time-of-use electricity rates.
For related running-cost calculators, see our Pool Pump Running Cost Calculator or Appliance Energy Cost Calculator.