What Does a Hot Tub Cost to Run?

The number first

Hot tubs are usually quoted in a confusing way, because the heater's rating has almost nothing to do with what you pay. A 5.5 kW heater sounds alarming, but it does not run continuously. What matters is the average draw across a full day, which on a reasonably modern, well-covered tub lands near 400 watts.

That is roughly 3,504 kWh a year, which for most households is second only to heating, cooling and hot water. It is also wildly variable: the same tub in Nevada and in Massachusetts differs by more than two to one on rate alone, before any difference in weather.

Those figures assume the same tub, the same cover and the same habits. Only the price of electricity changes. If your state is not listed, the rates by state guide has all fifty, and the calculator will run your own rate against your own numbers.

Where the energy actually goes

Three things in a hot tub use electricity, and they are nothing like equal.

Standby heating is nearly all of it. Water at 102°F sitting in cold air loses heat continuously, through the surface, through the cabinet walls and through the plumbing. The heater's only job most of the day is replacing that loss. On a cold night a tub can shed several kilowatt-hours just standing there, and every one of those has to be bought back.

Filtration is a modest, constant cost. The circulation pump moves water through the filter and past the heater. Depending on the model it is either a small dedicated pump at 100 to 300 W running many hours, or one speed of the main pump drawing more for fewer hours. Call it 10 to 15% of the total.

Jets are almost irrelevant. The jet pumps are the biggest motors in the tub, often 1,500 to 3,000 W each, but they run only while someone is in it. Two hour-long soaks a week at 2 kW is about $3.18 a month. Nobody's bill is high because of the jets.

The practical consequence is that how often you use the tub barely affects what it costs. A tub used twice a week and a tub used every day cost within a few dollars a month of each other. The bill is set by how well the tub holds heat, which is a property of the hardware and the cover, not of your habits.

The cover is the whole ball game

Most of the heat leaves through the water surface. A cover that seals properly and is not saturated is the difference between a tub that costs $40.14 a month and one that costs $93.67.

Covers fail slowly and invisibly. The foam cores absorb water over a few years, which both adds weight and destroys their insulating value. A cover you can barely lift is a cover that is costing you money every hour.

Three checks worth doing today:

• Lift it. If it is noticeably heavier than when it was new, the foam is waterlogged. Replacement typically pays for itself within one to two heating seasons.
• Look along the seam. The hinge in the middle is the weakest point. A hinge seal or a foam wedge insert closes the gap where warm air escapes.
• Feel the edges. Run a hand around the lip on a cold evening. Warm air leaking at the corners means the cover is not seating, usually because the skirt has shrunk or the tub lip is deformed.

A floating thermal blanket laid directly on the water under the hard cover adds a second barrier and costs very little. In cold climates it is the highest-return accessory available.

Temperature, and the myth about turning it off

Heat loss scales with the difference between water and air. That gives you two levers: lower the water, or wait for warmer air.

Dropping the setpoint from 104°F to 100°F typically cuts running cost by 8 to 12%, which on the baseline above is $5.35 a month. Dropping to 98°F between uses and raising it a few hours before you get in saves more, and modern controls will schedule that for you.

What does not work is switching the tub off between weekends. Reheating 350 to 500 gallons from cold runs the heater at full power for the better part of a day, and you pay for every degree you let it lose. The arithmetic only turns in favour of shutting down at around a week or more away, and even then you have to weigh freeze risk in winter. For a two-week winter holiday, most owners are better off dropping to the lowest setting that keeps the plumbing safe rather than draining and shutting down.

What else moves the number

• Climate. A tub in Ottawa in January works far harder than the same tub in Phoenix. Expect winter months to run 50 to 100% above the annual average in cold regions, and summer months well below it.
• Siting. Wind strips heat from the cabinet and the cover. A tub on an exposed deck can cost noticeably more than one tucked against a wall or behind a screen. Shelter is free insulation.
• Cabinet insulation. Full-foam tubs hold heat better than "thermal barrier" designs with an empty cavity. This is set at purchase and is the main thing that separates a cheap tub from an expensive one over ten years of ownership.
• Filtration schedule. Many tubs ship with filtration cycles far longer than needed. Two cycles of an hour or two, enough to turn the water over a couple of times a day, is usually plenty for light domestic use. Check the manual before changing it; under-filtering costs chemicals and clarity.
• A failing element or sensor. If your cost jumps with no change in habits or weather, suspect the heater staying on. This is a service call, not a settings change.

Is it worth putting on a timer?

Generally no, and it is worth understanding why, because it is the most common suggestion people get.

Switching the heater off during peak hours does not reduce heat loss; it just defers the heating. The water keeps cooling, and the heater works harder afterwards to catch up. You end up buying about the same number of kilowatt-hours.

The exception is a time-of-use rate plan. There the aim is not to use less but to buy it cheaper: let the tub coast through the expensive late-afternoon window and do the catching up overnight at the low rate. On a plan with a 40¢ peak and a 12¢ overnight price, moving even half the heating out of peak is worth real money. Our time-of-use guide explains how to tell whether you are on such a plan and what the windows usually are.

What to do, in order of payoff

1. Check the cover. Waterlogged or badly sealing is the single biggest avoidable cost. Replace it or add a floating blanket.
2. Lower the setpoint by two to four degrees and see whether you miss it. Most people do not.
3. Trim the filtration cycle to what the water actually needs.
4. Shelter the tub from prevailing wind if it sits exposed.
5. Check your rate plan. If a time-of-use option exists, a hot tub is one of the loads that benefits most from shifting.
6. Watch for a sudden jump in cost that weather does not explain, and get the heater checked.

To put your own numbers against this, open the electricity cost calculator, choose the hot tub preset and set your own rate and average wattage. If you want to see how it ranks against everything else in the house, the most expensive appliances guide puts it in order, and the wattage chart has the figures for everything else you own.