By The Zagosa Team. Published .
Reviewed or updated .
Yes, cooler water is cheaper to run. The saving between 40C and 38C is slight. Between 38C and 35C it becomes noticeable. Drop below 32C, though, and the tub starts to feel less inviting, particularly in winter.
What each degree really saves
On a typical UK 1,200-litre tub with a decent cover, every degree you lower the set point trims roughly 4 to 6% off the running cost. Across a winter month costing 60 pounds to run, that is around 3 pounds per degree.
The savings stack up. Going from 39C down to 36C claws back around 12 to 18 pounds a month in winter, which is a worthwhile chunk.
The temperatures UK owners settle on
38C is the standard set point. Properly warm in winter, comfortable for adults in summer.
36C suits homes with children or older bathers, and it is the temperature most physiotherapists suggest for circulation.
34C is summer-only territory. It feels lukewarm in February but just right on a warm August evening when the air is already 22C.
Holiday and economy modes
Most modern controllers have an economy or sleep mode. It usually knocks the set point down 4 to 6C between filter cycles and reheats only when needed. The savings are real, but only if you genuinely use the tub less than twice a week.
For a tub used several times a week, economy mode can actually cost more, because each reheat overshoots and the heater works harder. If you bathe regularly, stick to a constant set temperature.
Common questions
Will lowering the temperature change the chemistry?
A little. Cooler water needs slightly less sanitiser because organic activity slows, but the shift is small. Test as normal and adjust if your free chlorine starts climbing.
Is there a temperature that does more harm than good?
Above 40C is uncomfortable for most adults and unsafe for soaks longer than 10 minutes. That is why most UK manufacturers cap the set point at 40C.