By The Zagosa Team. Published .
Reviewed or updated .
In almost all cases, yes, leave it on. Modern hot tubs are built to sit permanently powered, with the thermostat switching the heater on and off to hold your chosen temperature. Switching the whole thing off and reheating from cold each time typically costs you more, not less.
What it really costs per month
Under the current UK price cap, a typical four to six-person tub held at 38C behind a good cover runs to roughly 50p to 90p a day in summer and 1.50 to 2.50 pounds a day in winter. Averaged across the year that works out somewhere between 25 and 75 pounds a month.
Three things swing those figures: how cold the air is, how good your cover is, and how much you run the jets. A split or sodden cover can, on its own, double what you pay.
The times switching off genuinely pays
If you honestly use the tub less than once a fortnight over summer, easing the set temperature down to around 28C between soaks can claw back a few pounds a week. You still need to sanitise, but the heater barely fires.
The rest of the year, reheating from cold on every visit tends to cost more than switching off ever saves. Cold water also grows biofilm quicker, which shows up on your chemical bill.
Five small tweaks that actually shift the bill
Swap the cover once it feels heavy. A waterlogged cover is doing half a job, and you will notice the difference within a single billing cycle.
Take the temperature down a degree. The energy gap between 39C and 38C is larger than people expect because of the wider differential to cooler air.
Slip a thermal blanket under the main cover. A four-pound floating blanket cuts evaporation, and evaporation is where the bulk of your heat disappears.
Shift the filter cycle to off-peak. On a time-of-use tariff, set the long filtration window to run during the cheap hours.
Hold the chemistry steady. When sanitiser levels swing, the pump works harder and the water is trickier to heat to a comfortable feel.
Common questions
Can I leave it on while away on holiday?
For a fortnight or so, yes, as long as the cover is locked, the chemistry is balanced before you leave, and someone can check it after a week. For anything longer, drop it into economy mode or book a proper service visit.
Do the jets add much to the cost?
Less than most people assume. The jet pump might pull 1.5 to 2kW, but only for the few minutes you have it running. It is the constant heater and the long filter cycles that dominate the bill.