What cable size do I need for a 9kW sauna?

A 9kW sauna draws 39A at 230V. You need 10mm² cable on a 40A or 45A circuit for most installations. For runs over 20m, check voltage drop. Heat-resistant cable is only needed for the section within the sauna room itself.

Do I need special cable inside the sauna?

Yes, heat-resistant cable rated to 170°C+ is essential within the sauna room. Standard PVC cable (70°C rating) will degrade and fail. The heat-resistant section runs from the control unit (outside) to the heater (inside). It's typically silicone insulated.

Where should the sauna control unit be located?

The control unit must be outside the sauna room in a dry location. Typically mounted on the wall just outside the sauna door or in an adjacent room. This keeps electronics cool and allows temperature adjustment without entering the hot room.

What MCB rating for a sauna heater?

MCB rating depends on heater power: 4.5kW = 20A, 6kW = 32A, 9kW = 40A, 12kW = 50A. Type B MCBs are suitable for resistive heating loads. Larger saunas may need Type C if motor-driven controls are included.

Do saunas need RCD protection?

Yes, 30mA RCD protection is required. Some sauna control units include integrated RCD protection, but external RCD at the consumer unit is still recommended. For outdoor saunas, RCD protection is mandatory for the outdoor circuit.

Can I install a sauna on a standard 13A socket?

Only very small portable saunas (up to about 2.5kW) can use 13A sockets. Most fixed sauna heaters require hardwired connections on dedicated circuits. A proper installation with appropriate cable sizing and protection is essential for safety.

What about outdoor or garden saunas?

Outdoor saunas need SWA cable for the buried run to the cabin, then heat-resistant cable within. An outdoor isolator switch is required. The installation must comply with both outdoor circuit requirements and sauna-specific requirements.

Do I need three-phase for a large sauna?

Commercial saunas over 12kW may benefit from three-phase supply, spreading the load across phases. Most domestic saunas up to 12kW work on single-phase. Check if your property has three-phase available before specifying large commercial heaters.

Is Part P notification required for sauna installation?

Yes, installing a new sauna circuit is notifiable under Part P Building Regulations. The work involves a new circuit and potentially special location requirements. It must be done by a registered competent person or inspected by Building Control.

How long should heat-resistant cable be?

Only the section within the sauna room needs heat-resistant cable - typically 2-4 metres from where the cable enters the room to the heater terminals. The cable from consumer unit to the control unit (outside the room) can be standard cable.

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Sauna Cable Sizing Calculator

Calculate the correct cable size for electric sauna heater installations

Sauna Cable Quick Facts

Domestic saunas typically 4.5kW-9kW (20A-40A)
Commercial saunas may need 12kW-18kW (52A-78A)
Heat-resistant cable required within sauna room
Dedicated circuit with local isolator essential
External sauna control unit for temperature regulation

Cable Size Calculator

BS 7671:2018+A2:2022 compliant

1. Load Current

1kW ≈ 4.35A at 230V

2. Cable Length (meters)

3. Installation Method

Lighting circuit (3% voltage drop limit)

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Common Sauna Installations

Small home sauna (4.5kW)

20A MCB, 4mm² standard cable to control, heat-resistant within sauna

Medium home sauna (6-9kW)

32A-40A MCB, 6mm² or 10mm² cable depending on length

Large home sauna (9-12kW)

40A-50A MCB, 10mm² cable, may need consumer unit upgrade

Commercial sauna (12-18kW)

63A+ circuit, possibly 3-phase for larger units

Outdoor/garden sauna cabin

SWA cable for buried run, heat-resistant within cabin

Complete Your Wellness Installation

Saunas often pair with hot tub installations for complete home wellness. For outdoor sauna cabins, our garden building cable guide covers SWA burial requirements. Electric shower circuits use similar sizing principles.

Sauna Cable Sizing

Sauna cable sizing determines the conductor cross-sectional area (mm²) needed to safely supply an electric sauna heater. Saunas have specific requirements: heat-resistant cable within the hot room (rated 170°C+), external control unit positioning, and appropriate circuit protection. The supply cable to the control unit can be standard cable.

Sauna Installation Costs (2024)

Typical UK electrical installation costs. Does not include sauna cabin or heater unit.

Installation Scenario	Materials	Labour	Total
Small sauna (4.5kW), short run	£100-180	£180-300	£280-480
Medium sauna (6-9kW), typical install	£150-280	£250-400	£400-680
Large sauna (9-12kW)	£200-350	£300-480	£500-830
Outdoor sauna cabin with SWA	£300-500	£400-600	£700-1100
Heat-resistant cable (per metre)	£8-15	Included	£8-15/m

Prices as of 2024. Heat-resistant cable is more expensive than standard cable.

Heat-Resistant Sauna Cable

Standard PVC cables are rated to 70°C and will fail in sauna conditions (80-100°C). Within the sauna room, heat-resistant silicone or PTFE insulated cable rated to 170-180°C must be used. This special cable runs from the control unit to the heater. Standard cable can be used from the consumer unit to the control unit outside the hot room.

Sauna Heater Power Sizing

Sauna heater power is typically calculated at 1kW per cubic metre of sauna room volume, with adjustments for insulation quality and window area. A 2m × 2m × 2m sauna (8m³) typically needs an 8-9kW heater. Undersized heaters struggle to reach temperature; oversized heaters waste energy.

Sauna Electrical Safety

Sauna installations must comply with BS 7671 and manufacturer requirements. Key safety points: heat-resistant cable within hot zone, control unit outside hot room, local isolation switch, RCD protection, and appropriate IP-rated accessories. The combination of heat and humidity requires careful equipment selection.

Frequently Asked Questions

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