By The Zagosa Team. Published .
Reviewed or updated .
Your hot tub does not lose power in winter. The heat is escaping as fast as the heater can replace it. Once the air drops below 5C and the wind gets up, a UK garden tub sheds warmth at roughly double its usual rate. Here is how to deal with it.
Where the heat is really escaping
Around 60% of winter loss goes through the cover. Another 30% leaks through the shell where the cabinet panels meet the floor, especially if the foam insulation has shifted. The final 10% goes through the plumbing and the equipment bay.
If any of those three is compromised, you are warming the garden as much as the water. The cover is the easiest to inspect and the easiest to put right.
The five-minute winter check
Press down on the middle of the cover. If it sags more than 2cm, or you can hear water sloshing in the foam, the cover has waterlogged. Replace it before you feed the heater for another month.
Walk round the cabinet. Any panel that feels distinctly colder than the rest may have lost its insulation jacket, often after a service.
Check the equipment bay. Pipes should not be sweating or icing up. If they are, the bay heater (a small unit that keeps the plumbing above freezing) may have failed.
Two cheap fixes that work
A floating thermal blanket on the water surface, under the main cover. Five to ten pounds, and it halves evaporative loss. Evaporation is the single biggest way heat leaves, even in winter.
A wind break on the upwind side. A solid panel or a tall planter on the cold side slows the rate at which air drags heat off the cover. You can feel the difference inside a day.
If neither shifts the dial, take the cabinet panels off and inspect the foam insulation. Older tubs benefit enormously from a 25-pound aftermarket insulation kit.
Common questions
Should I lower the temperature in winter to save money?
Yes, by a degree or two. Going from 38 to 36 saves more in January than in July, because the gap to the air temperature is wider.
Would draining for winter save more?
Only if you will not use it for at least three months. The drain-down, refill and full chemical reset carries its own cost in time and product.