13 amp vs 32 amp hot tubs explained

The basic numbers

Power in watts is roughly voltage times current. UK mains is nominally 230 V, so a 13 A socket can deliver about 3,000 W, or 3 kW. A 32 A circuit can deliver about 7,360 W, or roughly 7.4 kW. Everything in the tub, from heater to air blower to circulation pump, must share whatever the supply allows.

That is why inflatable heaters are usually rated around 2 kW. Add a blower of several hundred watts and a circulation pump and you are close to the limit of a 13 A plug. On many 13 A tubs the controls pause the heater while the bubbles run, or limit how long the blower can stay on. Check your manual for how your model behaves.

Why a 13 A tub heats slowly

Heating water takes a fixed amount of energy: about 4.186 kJ per litre per degree. To heat 800 litres from 10 to 38 °C takes at least 26 kWh. At 2.2 kW that is about 12 hours, and real times are longer because heat escapes while the tub warms. A 3 kW heater on a 32 A tub would need about 8.7 hours for the same water, before losses.

This is physics, not a fault in the tub. Try the heat-up calculator with your own litres and heater rating.

Does 32 A use more electricity?

Not in itself. A bigger heater uses more power while it runs, but it runs for less time. The energy needed to raise the water temperature is the same either way. What changes weekly kWh is how much heat the tub loses, which depends on insulation, cover, air temperature, wind and how long the lid is open.

Hard shell tubs on 32 A supplies usually have thick foam insulation and rigid lids, so they often use less energy to hold temperature than an inflatable, even though their heaters are bigger. An inflatable kept hot all week in cold weather can use a surprising amount, simply because its air walls let heat out. See running costs for how to work out your own figure.

Installing a 13 A tub safely

An inflatable tub should plug into a weatherproof outdoor socket on a circuit protected by an RCD, as the manual directs. Many pump plugs include their own protective device; test it as the manual describes before each use. Keep the plug and cable off the ground and away from splashes.

Most makers say not to use an extension lead. If your nearest outdoor socket is too far away, have a qualified electrician fit a new one rather than running a lead across the lawn.

Note:Electricity and water are a dangerous mix. Do not use extension leads unless the manual allows it, never handle plugs with wet hands, and have new outdoor sockets or circuits installed by a qualified electrician.

Installing a 32 A tub

A 32 A hot tub needs its own circuit from the consumer unit, with suitable cable, RCD protection and a rotary isolator within reach of the tub but out of reach of bathers. In England, new outdoor circuits fall under the building regulations, so the work needs a qualified electrician who can certify it. This adds to the cost and time of a hard shell tub, and it is one reason inflatables are popular.

Which is right for you?

Our best inflatable hot tubs guide covers 13 A tubs from the main brands.

• Choose a 13 A inflatable or plug and play tub if you want a simple setup and use the tub mainly from spring to autumn.
• Choose a 32 A hard shell tub if you want to heat and run all jets together and will use it all year.
• If you are unsure what your home's supply can take, ask a qualified electrician before buying a 32 A tub.

Frequently asked questions

Can an inflatable hot tub run on 32 A? Inflatables are designed for a 13 A plug. Use the supply the manual specifies.

Why does my heater stop when the bubbles are on? On many 13 A tubs the controls pause the heater so the total load stays within the socket's limit. Check the manual.

Is a 13 A hot tub cheaper to run? Not necessarily. Weekly kWh depends more on insulation and cover than on the supply.

Do I need an electrician for a 13 A tub? Not if you already have a suitable RCD protected outdoor socket. For a new socket, yes.