Inflatable hot tub running costs in the UK: electricity, chemicals and the maths
Most running cost articles give you a single figure and no working. That is not much use, because the real cost depends on your tub, your weather and how often you use it. This guide shows the arithmetic so you can swap in your own numbers.
We use the Lay-Z-Spa Miami AirJet as a worked example because its manufacturer publishes the power rating, water volume and heating times. All prices were checked on 12 November 2026. We have not metered a tub ourselves, and every scenario below is a calculation, not a measurement.
The short answer
On the Ofgem price cap, a 2 kW class inflatable hot tub costs about 54p for every hour its heater is running. How many hours that is each day decides everything. At 4 heater-hours a day you would spend roughly £2.16 a day; at 8 hours, roughly £4.32 a day. Filters, chemicals and water add a smaller, fairly predictable amount on top.
Step 1: The electricity price
For 1 October to 31 December 2026 the Ofgem price cap sets the average electricity unit rate at 26.32p per kWh, with a standing charge of 54.83p per day, for Direct Debit customers in England, Scotland and Wales. The cap applies to standard variable and tracker tariffs, and rates vary by region. If you are on a fixed tariff, use the rate on your own bill. The cap changes every quarter, so update the figure after 31 December.
The standing charge is paid whether or not you own a hot tub, so we leave it out. Only the unit rate matters here.
Step 2: The tub's power draw
The Lay-Z-Spa Miami AirJet is listed at 220 to 240 V, 2,050 W total (a 2,000 W heater plus 50 W for the filter pump, per the manual), and holds 669 litres.
Cost per hour of full power = 2.05 kW x 26.32p = 53.96p, call it 54p.
Note that this is the cost while the heater is on. Once the water reaches your set temperature the heater switches off and cycles on only to replace lost heat.
Step 3: The first heat-up
There are two ways to estimate the first fill.
The physics (the minimum)
Heating water takes 4.186 kJ per kg per degree. 669 litres is about 669 kg, so each degree needs 669 x 4.186 = 2,800 kJ, which is 0.78 kWh. Heating from 15°C to 38°C (23 degrees) needs 23 x 0.78 = 17.9 kWh, or 17.9 x 26.32p = £4.71. That is the theoretical floor with zero heat loss.
The manufacturer's heating time (more realistic)
The manual says the tub takes 12 to 20 hours to reach 40°C from 15°C, with the cover on. If the tub draws its full 2.05 kW throughout, that is 24.6 to 41 kWh, or £6.47 to £10.79. Real-world heat loss, wind and a cold start push you towards the top of that range.
Each time you refill with cold mains water you pay this heat-up cost again.
Step 4: Keeping it hot
This is the number that varies most. The heater cycles on and off, so the useful question is "how many hours a day does it actually run?" Your smart plug, an energy monitor on the socket, or the tub's own display may tell you after the first few days. Until then, here are scenarios.
| Heater-on hours per day | kWh per day | Cost per day | Cost per week | Cost per 30 days |
|---|---|---|---|---|
| 4 | 8.2 | £2.16 | £15.11 | £64.75 |
| 8 | 16.4 | £4.32 | £30.22 | £129.49 |
| 12 | 24.6 | £6.47 | £45.33 | £194.24 |
Calculation: hours x 2.05 kW x 26.32p. Scenario figures, not measurements.
Published claims show how wide the spread is. One retailer's page for the Miami said "approx. £10.00 per week" (about 2.6 heater-hours a day at today's rate), while Wave Spas says its Pacific model costs about £4 a day under typical use. These claims were made at different times, on different tubs and with different assumptions, which is exactly why we recommend doing the sum yourself.
What pushes the hours up
- Cold weather. The Miami manual says that below 15°C heating is slower, and below 6°C you should keep the heater on, using a winter function that holds the water between 6°C and 10°C. Winter use costs more than summer use.
- Leaving the cover off. The manual notes heating time increases if the cover is not kept on during heating.
- A higher set temperature. The maximum is 40°C and the manual says 38°C is comfortable for adults. Each extra degree costs about 0.78 kWh to add to a full tub (roughly 20p), plus the extra heat then lost over time.
- Direct sun and heat. Above 35°C ambient in direct sunlight, the manual says heating may stop with an error code, so summer heat waves are a different problem.
What helps
- Keep the cover on whenever the tub is not in use.
- Use an insulating mat underneath. The manual recommends one.
- Do not control the tub through a plug-in timer. The manual says not to power the unit through a timer or other external switching device. Use the tub's own scheduling if it has it.
- Lower the set temperature a degree or two when you are not bathing.
Step 5: Filters and chemicals
| Item | Published price | Notes |
|---|---|---|
| Chemical starter kit (500 g chlorine granules, pH Plus and Minus, foam remover, 25 test strips) | £29.99 | The retailer does not say how long it lasts; owners report it varies widely. |
| Filter cartridges, 12-pack | £26.99 (about £2.25 each) | The retailer says 12 should keep the water in good condition for a season, depending on use. |
The manual recommends checking and cleaning the filter daily and replacing it weekly, or sooner if it stays stained after cleaning. Replacing weekly for a full year would be 52 cartridges, or about 4.3 packs: roughly £117 a year. A summer-only season of 12 weeks needs one pack at £26.99.
The manual's target water balance is pH 7.4 to 7.6, alkalinity 80 to 120 ppm and free chlorine 2 to 4 ppm. Without chemical treatment it says to change the water every three days, which means paying for a fresh fill and a fresh heat-up each time.
Lay-Z-Spa's own comparison page claims "filters and water care" for an inflatable costs £50 to £100 a year. That is a manufacturer claim, but it is the same order of magnitude as our figures.
Step 6: Water
A fill is 669 litres, or 0.669 cubic metres. If you have a water meter, multiply 0.669 by the per-cubic-metre charge (water plus sewerage) on your bill. If you are unmetered, a fill does not change your bill. We have not used a standard figure because charges vary a lot between companies.
Worked example: one 12-week summer season
| Item | 4 heater-hours/day | 8 heater-hours/day |
|---|---|---|
| Electricity (84 days) | £181.29 | £362.58 |
| First heat-up (range £6.47 to £10.79) | £6.47 to £10.79 | £6.47 to £10.79 |
| Filters (one 12-pack) | £26.99 | £26.99 |
| Chemicals (one starter kit) | £29.99 | £29.99 |
| Total, excluding water | About £245 to £249 | About £426 to £430 |
If your bathing season is longer, or you run the tub through winter, the electricity line grows quickly, because both the hours and the heat loss increase.
Frequently asked questions
How much does it cost per hour to run an inflatable hot tub?
About 54p per hour of heating for a 2.05 kW tub at 26.32p per kWh. Multiply the tub's wattage in kW by your unit rate.
Is it cheaper to leave the heater on or reheat each time?
It depends on your climate, cover and usage pattern, and we have found no published measurement to settle it. The manual's heating times (up to 24 hours from 10°C) show a cold restart is a real energy cost, so compare your own meter readings over a week or two of each approach.
Does a hot tub cost more in winter?
Yes. Heating is slower below 15°C, and below 6°C the manual says to keep the heater on to protect the tub.
Do standing charges increase when I buy a hot tub?
No. Standing charges are fixed per day. Only your unit consumption changes.
Related guides: choosing an inflatable hot tub for a small garden and inflatable vs hard-shell.
Sources (checked 12 November 2026)
- EDF, energy price cap 1 October to 31 December 2026 (26.32p/kWh, 54.83p/day): edfenergy.com
- Energy Saving Trust, what is the energy price cap (same Ofgem figures): energysavingtrust.org.uk
- Bestway Lay-Z-Spa Miami AirJet (669 litres, 2,050 W): bestwaystore.co.uk
- Bestway Lay-Z-Spa Miami owner manual (heater, heating times, filter and chemical guidance, timer warning): manuals.plus
- Lay-Z-Spa chemical starter kit (£29.99): lay-z-spa.co.uk
- Bestway Lay-Z-Spa filter cartridges, 12-pack (£26.99): bestwaystore.co.uk
- Lay-Z-Spa vs hard shell hot tubs (£50 to £100 a year claim): lay-z-spa.co.uk
- Appliances Direct, Miami listing (approx. £10 per week claim): appliancesdirect.co.uk
- Wave Spas, The Pacific (about £4 per day claim): waveglobal.zendesk.com
- Specific heat of water (4.186 kJ per kg per degree): standard physics constant.