Where a hot tub's electricity goes
Ask most owners what drives their hot tub bill and they’ll say how often they use it. That turns out to be close to irrelevant. The tub is heated 24 hours a day, 365 days a year, whether anyone gets in or not. That standing cost dwarfs the energy any single soak adds.
The three lines on the bill
Standby heat loss is the big one, typically 60–80% of the total. Water at 38 °C sitting in air at 5 °C sheds heat continuously through the shell, the plumbing and — mostly — the cover. The heater replaces exactly what escapes. Because loss is proportional to the temperature gap, this line roughly doubles between a mild autumn and a hard winter.
The circulation pump is the quiet second place. Tubs ship configured to filter generously, and a 200 W pump running around the clock draws about 146 kWh a month — roughly what a fridge uses, running constantly, for water nobody is sitting in.
Reheating from cold is dramatic and almost always irrelevant. Bringing 1,500 litres up by 20 °C takes about 35 kWh, which sounds alarming, but if you do it twice a year it contributes almost nothing. Draining for a move or a repair is not what is on your bill.
What actually moves the number
Look at your cover first. A cover is foam wrapped in vinyl, and the vinyl eventually fails. Once water gets into the foam it stops insulating and starts adding weight. The diagnostic is simple: if the cover has become noticeably heavy, or one side sags, it is waterlogged and costing you every hour of every day. Replacing a dead cover is the single highest-return thing an owner can do.
Then the setpoint. Heat loss scales with the gap between water and air, so dropping from 40 °C to 38 °C removes about two degrees’ worth of that gap — a straight percentage off the largest line on the bill. Most people cannot tell the difference once they are in.
Then the pump schedule. Check the manual for the turnover your filtration actually requires. On a modern tub it is often satisfied by 6–12 hours a day, not 24. This is a settings change that costs nothing.
What doesn’t help as much as people think
Turning the tub off between uses is usually a false economy: you save standby loss for a day or two, then pay most of it back reheating, and you spend the time waiting. A tub with a good cover holds temperature cheaply; the fix is a better cover, not an off switch.
Similarly, a tub cover lifter is a convenience, not an efficiency measure — though anything that makes you seat the cover properly every time does help at the margins.