Hot Tub Energy Efficiency: How to Cut Your Heating Costs

Last updated: September 2026

There’s nothing like a soak under the stars on a cold night. But as every hot tub owner knows, that luxury comes with a bill, and heating is the biggest part of it. The good news is that a lot of that bill is heat you’re paying for and then losing. Stop the losses and heat smarter, and you can cut your running costs a lot before you spend anything on new kit.

This guide isn’t mainly about fitting an air source heat pump, although I’ll touch on it, because I’ve written plenty about that elsewhere. It’s about everything else: the cover, insulation, wind, heating schedules and the small habits that add up, whatever heater you have.

What does it cost to heat a hot tub?

It helps to know what you’re saving. It takes about 1.16kWh to raise 1,000 litres of water by 1°C. So every degree your tub loses has to be put back, and the cost depends on your heater and your energy price.

Heat source	UK cost per kWh of heat	USA cost per kWh of heat
Spa pack electric element	26.3p	18.3¢
Heat pump, cold weather (COP 2.5)	10.5p	7.3¢
Heat pump, mild weather (COP 4)	6.6p	4.6¢

These use the Ofgem price cap for 1 October to 31 December 2026 of 26.32p per kWh, and the EIA’s average US residential price for July 2026 of 18.31¢ per kWh. Your own tariff will be different, so plug in the figure from your bill.

As an example, take a 1,500 litre tub on its spa pack element. Each degree it loses costs about 1.74kWh, or roughly 46p (32¢) to put back. Heating it from 10°C mains water to 38°C takes about 49kWh, around £13 ($9). Every bit of heat you keep in the tub is money you don’t spend.

1. Check the cover

If you do one thing, make it this. The cover is the single most important part of your tub’s energy efficiency. Most heat escapes from the water’s surface, through evaporation and warm air. For pools, the US Department of Energy says evaporation is by far the largest source of energy loss and that a cover can save 50–70% of heating costs. A hot tub at 38–40°C loses heat even faster than a pool, so the cover matters even more.

But it only works if it’s in good condition and fits snugly:

• Is it heavy? A cover that’s got noticeably heavier has soaked up water. A waterlogged cover has lost much of its insulation and can grow all sorts of grime inside.
• Does it seal? Look for gaps at the hinge and edges, and steam escaping on a cold morning. Check the skirt and clips.
• Is it sagging? A dip in the middle collects rain and snow and lets heat out at the edges.
• Is it off for long? Keep it on while heating and between soaks. Heating with the cover off is like boiling a kettle with the lid off.

An old, waterlogged cover is worth replacing. It will pay for itself. There’s more in the ultimate guide to hot tub covers and hot tub cover maintenance. If you’ve built your own tub, see How to make a DIY hot tub cover.

2. Add a floating thermal blanket

A floating thermal blanket (sometimes sold as a solar blanket) sits on the water under the main cover. It adds another layer of insulation and cuts evaporation, which also means less water and fewer chemicals to top up. It doesn’t use any electricity.

What it won’t do is heat your hot tub. On a pool left uncovered in the sun, a solar blanket can pick up a little warmth, but under a hot tub cover there’s no sun reaching it. Think of it as insulation, not a heater. It’s a cheap upgrade, especially if your cover is a bit tired but not ready to replace.

3. Insulate the cabinet or shell

Heat also leaks through the sides and floor. How much you can do depends on the tub:

• Shop-bought tubs: many are already fully foamed. If yours has open cabinet voids or just thin panels, you can add insulation inside the cabinet, such as spray foam, rigid board or foil-backed insulation. Keep it well away from the pumps, spa pack, heater and any vents, because they need air to keep cool. Also bear in mind that foam around pipework makes finding and fixing leaks much harder later. See Hot tub leak? How to find and fix it.
• DIY in-ground tubs: insulation under the slab and behind the walls makes a real difference. It’s the one thing I’d change on my own tub, which has none. On a new build, insulated concrete form (ICF) walls give you strength and insulation in one go. See DIY hot tub insulation and TubBlox and ICF hot tub walls.
• Pipework: insulate any pipes above ground, especially the runs to and from an external heater or heat pump.

4. Shelter it from the wind

Don’t underestimate the wind. It strips heat and moisture from the water whenever the cover’s off, and from the cabinet and cover the rest of the time. Fencing, a trellis, a privacy screen or well-placed planting can all act as a windbreak. It makes the tub more private and more pleasant to sit in too. If you’re choosing where to put a new tub, a sheltered spot will cost less to run than an exposed one.

5. Heat smarter: schedules and temperatures

Hold a lower temperature between soaks

If you use your tub a few times a week, it’s usually cheaper to keep it at a lower temperature between soaks than to let it go cold and reheat it from scratch, or to hold it at full temperature all the time. The lower the water temperature, the less heat it loses, and you’re not reheating 20–30°C of water each time.

That’s what I do. During the week I hold mine at a lower temperature and turn it up before the weekend. Since fitting a heat pump that heats much faster, I’ve been able to drop the weekday temperature further. I’ve shared the numbers in How I cut my hot tub running costs by 66%. Most spa packs have modes that help. See Balboa heat modes explained.

If you only use the tub now and then in a mild climate, shutting it down between uses can make sense. But in a cold winter, don’t let it get anywhere near freezing. See Winterizing a hot tub.

Heat in the cheaper hours

If you’re on a time-of-use tariff, such as Economy 7 or a smart tariff in the UK, or a time-of-use rate from your utility in the USA, set your filter cycles and heating to run in the cheaper hours, usually overnight. Many spa packs let you set filter cycle times, and in an economy or rest mode they’ll only heat during those cycles. A Wi-Fi module makes it easy to turn the tub up from your phone before you get home.

Don’t overdo the temperature

Every degree hotter means more heat lost. I find 38–39°C (100–102°F) most comfortable, and you should never go above 40°C (104°F), the maximum the US Consumer Product Safety Commission recommends. Check the reading with a floating thermometer, as a failing sensor can make the pack overheat.

6. Look after the equipment

• Clean the filter. A clogged filter cuts flow, so pumps run longer and heaters struggle. See How to clean a hot tub filter cartridge.
• Keep the water balanced. Scale on a heater element makes it less effective and shortens its life.
• Check the pumps. An old, noisy or oversized pump running long filter cycles adds up. On a DIY build, a small circulation pump or a variable speed pump can be far cheaper to run than a big jet pump on filtration duty. See Can I use a variable speed pump in a hot tub?
• Fix heating faults promptly. A tub that heats slowly may have a flow problem. See Help! My hot tub is not heating.

7. Then look at the heater

Once you’ve stopped the losses, the biggest remaining saving is the heater itself. A spa pack element turns 1kWh of electricity into 1kWh of heat. An air source heat pump moves heat from the outside air and gives you several kWh of heat for each kWh of electricity. The US Department of Energy puts pool heat pump COPs at 3 to 7, measured in warm conditions, and notes they’re most efficient while the air stays above about 45–50°F (7–10°C). On my own tub, a heat pump cut the running costs by 66%.

If you want to go down that road, start with the ultimate guide to air source heat pumps for hot tubs and How to choose the right air source heat pump for your hot tub or pool. To compare every option, including gas, boilers and solar, see What is the best way to heat a DIY hot tub? and How to heat a hot tub for free. You’ll find heat pumps and connection kits on parts4tubs.co.uk, and parts for US tubs on parts4tubs.com.

Energy-saving checklist

Action	Cost	Impact
Keep the cover on and sealed	Free	High
Lower temperature between soaks	Free	Medium
Heat in off-peak hours	Free (with the right tariff)	Medium
Clean the filter, balance the water	Low	Low to medium
Floating thermal blanket	Low	Medium
Windbreak or screening	Low to medium	Medium
Replace a waterlogged cover	Medium	High
Insulate the cabinet or shell	Low to high	Medium to high
Air source heat pump	High	High

Planning your own build?

The cheapest time to make a hot tub efficient is before it’s built. Insulated walls and floor, a good cover and a heat pump loop planned in from day one will save you money every month for years. My DIY hot tub plans include the plumbing layout, control room and parts list to do exactly that.

FAQs

Is it cheaper to leave a hot tub on all the time?

If you use it several times a week, usually yes, but at a lower temperature between soaks. Reheating from cold every time uses more energy than topping up a warm tub.

How much does it cost to heat a hot tub?

About 1.16kWh per 1,000 litres per °C. Heating a 1,500 litre tub from 10°C to 38°C on the element takes about 49kWh, roughly £13 at the late-2026 UK price cap or about $9 at the average US price.

Does a floating blanket heat a hot tub?

No. Under a hot tub cover it’s an extra layer of insulation that cuts evaporation and heat loss. It doesn’t add any heat.

How do I know if my hot tub cover needs replacing?

If it’s noticeably heavier than it used to be, sags in the middle, or lets steam escape round the edges, it’s lost much of its insulation and is costing you money.

Can I insulate my hot tub cabinet with spray foam?

Yes, but keep it well away from the pumps, spa pack, heater and vents, which need air to stay cool. Remember it’ll make any future leaks harder to find.

Got your own energy-saving tip? Share it in the comments below. I read them all.

Cheers,
Andi

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Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi