The cheapest way to heat a hot tub (UK guide)

The cheapest way to heat a hot tub, ranked

Everyone wants the same thing: a warm tub without a scary electricity bill. The good news is that most of the savings come from the cheap, boring stuff you can do this weekend — not from spending money. So we've ranked the tactics roughly cheapest-first. Start at the top, work down, and only reach for new kit once you've done the free things.

A quick honesty note before we start: we won't quote you a fixed "£X a year saved" figure, because it genuinely depends on your tub, your tariff, the weather and how you use it. For a number that fits your setup, use our hot tub savings calculator. If you want to understand where the money actually goes first, our guide to hot tub running costs in the UK breaks it down.

1. Keep the heat you've already paid for (cover, mat, shelter)

This is the single best-value thing you can do, and it's mostly free. Heating water is only half the battle — stopping it escaping is the other half, and every degree you keep is a degree you don't pay to make again.

• Use a good, well-fitting insulated cover — and actually close it every time. A tired, waterlogged or gappy cover is the most common reason a tub costs a fortune.
• Put a thermal floor mat or foam tiles underneath. Inflatable and foam tubs lose a surprising amount of heat straight down into a cold patio or decking.
• Add a wind shelter. Wind strips heat off the cover and waterline fast. A fence panel, hedge or a spot against the house wall makes a real difference for zero running cost.
• Consider a thermal blanket (a floating layer under the lid) for an extra bit of retention on cold nights.

Do these first. They cost little or nothing and they make every other tactic below work harder.

2. Turn the temperature down a touch, and time your heat-ups

You don't need to hold a hot tub at full soaking temperature around the clock.

• Drop the maintenance temperature. Holding the water a few degrees cooler between uses, then bringing it up before a soak, cuts standing losses without ruining the experience. Even a small reduction adds up over a week.
• Heat to a schedule, not "always ready". If you tend to use the tub on the same evenings, heat up ahead of those and let it coast the rest of the time.
• Don't fight the weather. Heating on a calm, milder day is cheaper than clawing temperature back on a cold, windy night.

This tactic is free, but it does ask you to plan a little. That's the trade-off: a bit of forethought for a lower bill.

3. Buy your electricity when it's cheap (Economy 7 and battery)

If you're heating with mains electricity, when you buy it matters as much as how much you use.

• Economy 7 and similar off-peak tariffs give you a ~7-hour overnight window at roughly 12.5p/kWh — about half the current Ofgem price cap (around 26p/kWh for July–September 2026; it changes every quarter, so always check today's rate). Heating overnight on that window is far cheaper than heating on peak-rate power.
• Add a battery and you can charge it overnight at the cheap rate (or from solar) and run the tub from stored energy during the day. That's the principle behind pairing storage with off-peak: fill up when power is cheap, spend it when power is dear.

The overnight window suits a hot tub nicely, because a well-insulated tub (see step 1) will hold much of that overnight heat into the next day.

4. Switch the heavy lifting to a heat pump

Here's the big one on efficiency. Your tub's built-in heater is a resistive element — think of a giant kettle. It's about 100% efficient, which sounds great until you realise that's the ceiling: one unit of electricity in, one unit of heat out. In efficiency terms that's a COP of 1.

An air-source heat pump doesn't make heat, it moves it — pulling warmth out of the outside air. In milder UK weather that gives a COP of around 3–5, meaning it delivers the same heat for roughly a third to a fifth of the electricity. Being honest: COP falls when it's cold, down to about 2–2.5 near freezing, so treat deep winter as more like COP 2–3. Even then, it's using around half the power of the built-in element for the same warmth.

You can add a heat pump to a tub you already own. We sell a heat pump that retrofits to Lay-Z-Spa and similar inflatable and foam tubs — it does the same job as the built-in heater, just far more efficiently, and heats roughly twice as fast.

5. Make your own with solar

The cheapest unit of electricity is one you didn't buy. Solar PV generates power from daylight, and paired with a battery and a heat pump it can run a tub largely on free or stored energy — especially in summer, when there's plenty of sun and the water needs less heating anyway.

Be realistic about the seasons: solar generation is strongest in summer (when demand is lowest) and falls away in winter (when demand is highest), so it's closer to near-free in summer and a partial contribution in winter, with the heat pump and off-peak power filling the gap. We cover exactly how PV, battery and heat pump work together in our solar hot tub kit guide.

Let the app do the money-saving for you

Every tactic on this page comes down to one habit: buy energy when it's cheap or free, and avoid it when it's dear. That's exactly the job our automation never stops doing — no spreadsheets, no timers, no getting up at 2am to catch the off-peak window.

Set a target temperature or tap "heat now," and the system picks the source itself:

• Free solar and stored battery power first
• Cheap off-peak electricity overnight when the battery needs topping up
• Full-price mains only as a last resort

It goes further than a plug-in timer ever could. It reads the local weather forecast and learns your routine, so it'll pre-warm on a sunny afternoon and hold off on paid energy if tomorrow looks bright. You can even commit a day ahead — tell it you've guests on Saturday and it plans the cheapest route to temperature. Curious how the numbers stack up? Try the savings calculator.

So, what's the actual cheapest way?

For most people it's a stack, not a single trick: insulate well, run a sensible temperature, buy power off-peak, and move the heating itself onto a heat pump — then add solar if you want to push running costs as close to nothing as the seasons allow. The first two cost almost nothing; the last two are where the big, lasting efficiency gains sit.

Want to see what this looks like for your tub and tariff? Try the savings calculator, or get in touch and we'll talk it through. Hot water needn't cost the earth.

Frequently asked questions

What's the single cheapest change I can make today?

A properly fitting, well-insulated cover that you close every time, plus a thermal mat underneath and some wind shelter. These cost little or nothing and stop you paying to reheat water that's leaked away — which is where a lot of hot tub cost hides.

Is it cheaper to leave a hot tub on or heat it up each time?

For regular users, holding a slightly lower maintenance temperature and topping up before a soak usually wins, because a well-insulated tub loses heat slowly. If you only use it occasionally, heating to a schedule and letting it coast in between tends to be cheaper. The best answer depends on your tub and habits — the calculator helps you compare.

Does a heat pump really cost less to run than the built-in heater?

Yes, for the same heat. The built-in element runs at about COP 1, while an air-source heat pump manages roughly COP 3–5 in mild weather and around 2–3 in the cold — so it uses a fraction of the electricity. The upfront kit is the trade-off, which is why we point you at the calculator rather than promise a fixed payback.