Hot Tub Running Cost Calculator

Almost nothing on a hot tub’s electricity bill goes into heating the water up. The tub reaches temperature once, then spends the rest of the month replacing heat that leaks out through the cover, the shell and the plumbing. That standby loss, plus the filtration pump, is the whole bill.

Most residential heaters draw 3,000 to 7,500 watts, and the pump adds another 1,000 to 2,500 watts. Neither runs continuously. A well-insulated modern tub in moderate weather costs somewhere around $20-50 a month. Cold-climate winters push that to $50-100. An old tub with a sagging cover can easily double either figure.

What actually moves the number

Insulation and cover condition matter more than everything else combined. Full-foam cabinets with a tight, dry cover keep heating cycles short. A waterlogged cover from six summers ago is barely better than no cover, and there is no thermostat setting that will save you from it.

Outside temperature is next, and it works through the gap between the water and the air rather than through the air temperature itself. Heat loss is proportional to that gap, so a 10-degree drop from a 47-degree gap adds about 21 percent to the bill.

Set temperature follows the same rule, which is why the widely repeated “10 percent per degree” claim is wrong. Going from 102°F to 103°F in 55°F weather widens the gap from 47 to 48 degrees, a 2 percent increase. Real, but small. The saving from dropping the setpoint two degrees is measured in a few dollars a month, not tens.

How this calculator works

It estimates daily heat loss from tub volume, an insulation multiplier and the temperature differential, works out how many hours the heater must run to replace that energy, adds the filtration pump on top, and multiplies by your rate. The chart runs the same model across all three tub sizes so the comparison is apples to apples.

One caveat worth stating plainly: every hot tub is different, and an estimate built from three size buckets cannot know about your particular cabinet. Treat the output as a budgeting figure. If you want the real number, read your meter before and after a 24-hour period with the tub covered and untouched.