Prepare before delivery
The correct power supply cannot be chosen from the product name alone. It depends on the selected heater, additional equipment and the type of connection available on site. The configuration must therefore be finalised before the electrician sizes the main cable and protective devices.
Short answer: an electric hot tub in the UK normally needs its own dedicated circuit from the consumer unit, with RCD protection, a suitable isolator and a cable sized by a registered electrician for the heater output you have ordered. Whether that circuit is single-phase or three-phase depends on the heater. If you are still choosing a model, compare the heater options on our electric hot tub page before booking the electrician.
This guide helps prepare the discussion between the customer, TimberIN and the local electrician. It does not replace the manual for the supplied appliance or the checks carried out by the professional making the connection.
Start with the information to give your electrician
Before running the cable from the house, gather the details of the variant actually ordered. Preparation based on a “similar” model may become inadequate as soon as a heater, massage system or heat pump changes.
The guide to preparing garden electrical connections complements this preparation file.
- exact model of hot tub or sauna;
- electric heater output, where specified;
- single-phase or three-phase connection selected for this heater;
- whether air massage, hydromassage, filtration and a heat pump are included;
- integrated main electrical box or appliances fitted with European plugs;
- whether sauna lighting is included;
- final position of the electrical box, weatherproof socket and cable route.
Safety principle: the customer prepares access and supplies the information. Calculations, protection and connection to the mains remain the responsibility of a qualified electrician on site.
Hot tub with an electric heater: one main supply
When an electric heater is installed, the hot tub receives a complete electrical installation. The heater and other ordered components are connected to the hot tub’s electrical box, which includes the fuses and circuit breakers specified for that assembly.
The customer must arrange for a main cable from their power source to this box. The cable type follows the heater connection: a 230 V single-phase supply where permitted for the chosen output, or a 400 V three-phase supply. The conductor size must be calculated for the load of the complete configuration.
Heater output, connection and current
A 6 kW heater is usual. Depending on the configuration, outputs may also be 3, 9, 12 or 15 kW. The supplied technical table also covers 18 kW; availability for the project must be confirmed in the final configuration.
A three-phase connection is normally recommended regardless of output. However, 3 and 6 kW heaters can be connected to a single-phase supply where this arrangement is confirmed for the appliance delivered.
| Heater output | 230 V single-phase | 400 V three-phase |
|---|---|---|
| 3 kW | 13 A | 5 A |
| 6 kW | 26 A | 9 A |
| 9 kW | — | 14 A |
| 12 kW | — | 18 A |
| 15 kW | — | 22 A |
| 18 kW | — | 27 A |
Current figures reproduced from the supplied table. Only the single-phase and 400 V three-phase supplies relevant to this preparation are shown. The rating plate, manual and delivered configuration remain the references for connection.
Add the hot tub’s other electrical components
The heater output is only part of the file. Record every option on the order and give the electrician the complete list.
| Component | Supply | Stated current |
|---|---|---|
| Air massage system | 230 V single-phase | 4 A |
| Hydromassage system | 230 V single-phase | 5 A |
| Filtration system | 230 V single-phase | 2 A |
| 5 kW heat pump | 230 V single-phase | 5 A |
These values describe the appliances individually. The hot tub’s main supply must be calculated from the actual equipment installed and how the electrical box distributes power. This is why the cable size cannot be inferred from an isolated value in the table.
Two possible preparations between the house and hot tub
With an electric heater
Main cable to the hot tub’s electrical box
The heater and other components are already arranged within the hot tub’s installation. A main cable suitable for the selected connection must run from the house to the integrated electrical box.
The box then distributes power to the appliances through its fuses and circuit breakers.
Without an electric heater
Dedicated circuit and weatherproof socket
With wood heating, or where a heat pump and other appliances are supplied without a main electrical box, each electrical appliance is fitted with a European plug.
The customer must provide a dedicated circuit from the house and an earthed weatherproof socket protected by a circuit breaker. TimberIN recommends placing this socket in the protected technical space beneath the hot tub, in an accessible position approved by the electrician.
Do not assume that a wood-fired hot tub needs no electricity. Filtration, massage or a heat pump may require a power supply even without an electric heater.
For a sauna, separate the heater and lighting
Electric sauna heater
Sauna heaters are supplied unwired. A local electrician must connect the heater to the dedicated cable from the house, in accordance with the actual model delivered.
Most heaters providing the required heating output are 9 kW or more and are normally connected to a 400 V three-phase supply. Some 6.8 kW models can be connected to a 230 V single-phase supply.
Interior lighting
When lighting is ordered, its cables are installed and brought together at the electrical box outside the sauna. This box then needs a 230 V supply prepared on site.
The heater circuit and lighting supply must therefore be identified separately in the information given to the electrician.
To compare models and heating configurations, see the pages dedicated to electric hot tubs and electric outdoor saunas. This guide remains focused on preparing the site.
The checks to complete before delivery
- Confirm the product. The model, heater and electrical options match the final quotation.
- Confirm the supply. The single-phase or three-phase connection is confirmed for the output ordered.
- List the appliances. Air massage, hydromassage, filtration, heat pump and lighting are all listed.
- Choose the connection point. Integrated box or dedicated weatherproof socket: the hot tub’s arrangement is clearly identified.
- Have the installation sized. The electrician calculates the main cable, earthing, fuses and circuit breakers required.
- Keep the documents. The manual and details of the equipment supplied remain available for connection and handover.
