Inflatable hot tub running costs in the UK

The two parts of running energy

The first part is heating the water from cold after filling. This is fixed by physics: about 4.186 kJ per litre per degree. Divide by 3,600 to get kWh. So the minimum is litres times 4.186 times the temperature rise, divided by 3,600. You only pay this after each fill, or after letting the water cool right down.

The second part is holding the temperature between uses. Heat escapes through the walls, floor, cover and into the air when the lid is open. The heater replaces it. Energy here is simply heater kW times the hours it runs. In mild weather with a good cover, the heater may only run for short spells. In cold, windy weather it can run for much of the day.

Worked examples

These sums use typical figures for illustration. Replace them with your tub's litres and heater rating from the manual.

Try the heat-up calculator →

Holding temperature through the week

To estimate holding energy, you need the hours the heater runs. Some app controlled tubs show this; otherwise you can watch how often the heater light comes on. As an example, if a 2.2 kW heater runs four hours a day in summer, that is 8.8 kWh a day. If it runs ten hours a day in a cold spell, that is 22 kWh a day.

Add any reheats after draining and the energy for the filter pump and bubbles, which are much smaller loads than the heater but run for many hours. Over a week, the holding energy usually matters more than the first heat-up.

What changes the total most

Insulated walls and foam tubs, such as Bestway's EnergySense models and the Wave Como, are designed to cut holding energy. See our winter guide for tubs with freeze protection and better insulation.

• Air temperature and wind: the colder and windier, the more heat escapes.
• The cover: a thick, well sealed insulated cover cuts losses more than anything else.
• Ground insulation: a foam mat under the tub reduces heat lost into cold paving.
• Lid off time: every minute with the cover off loses heat to the air.
• Bubble use: long bubble sessions can cool the water, and some tubs pause the heater while they run.
• Set temperature: holding a few degrees lower between uses reduces losses.

Ways to use fewer kWh

If you use the tub only at weekends in cold weather, compare holding a lower temperature all week with letting it cool and reheating. The temperature settings guide covers this.

1. 1

   Keep the cover on and strapped down whenever the tub is not in use.

2. 2

   Put an insulating mat under the tub before filling.

3. 3

   Shelter the tub from wind with a fence or screen, leaving safe clearance.

4. 4

   Use timers or the app to heat before you need the tub, rather than holding it hot all week.

5. 5

   Lower the set temperature between uses if your manual allows it.

6. 6

   Keep filters clean so the heater runs efficiently.

Electrical safety

Running costs are never a reason to cut corners on electrics. The tub should be plugged into a weatherproof outdoor socket protected by an RCD.

Note:Do not use extension leads unless the manual allows it. Have any new outdoor socket installed by a qualified electrician.

Frequently asked questions

Does a Lay-Z-Spa use a lot of electricity? It uses roughly 2 kW while heating. Total energy depends on how long the heater runs, which depends on weather and the cover.

Is it cheaper to keep a hot tub on or turn it off? In mild weather, letting it cool and reheating may use less. In cold weather, holding a lower temperature can be better. Work out both for your tub.

How much more does winter use take? It varies by tub and weather, but heater hours can be several times higher in cold, windy spells.

Where do I find my unit rate? On your electricity bill or supplier account, in pence per kWh.