Field note · power

Sauna power in Thailand: amperes, meters, three-phase and the surge question

A glass cabin of four seats pulls 8 kW, a 4 HP chiller about 3 kW, and the house already runs air-conditioning. Before any heater is ordered, the supply has to be checked. Here is the arithmetic, the meter sizes the utility actually offers, and the questions to ask.

Power · 9 min · 2026-10-11

An electrician's hands wiring a three-phase isolator switch box beside a sauna heater supply, with neat conduit, colour-coded cables and a tester in the other hand

What the supply looks like

Thai supply is typically 220⁠-⁠230 V single-phase and 380⁠-⁠400 V three-phase at 50 Hz. Official sources use both 220 and 230 V in different places, so equipment should tolerate 220⁠-⁠240 V and 380⁠-⁠415 V, which is how we specify. The Provincial Electricity Authority (PEA) serves 74 provinces; Bangkok, Nonthaburi and Samut Prakan are supplied by the Metropolitan Electricity Authority (PEA's service page).

Amperes by heater size

Cabin	Heater	Single-phase, 230 V	Three-phase, 400 V, each phase
Solo (1 seat)	Harvia 3.5 kW	15 A	5 A
2 seats	Harvia 4.5 kW	20 A	6 A
4 seats	Harvia 8 kW	35 A	12 A
6 seats	Harvia 10.5 kW	46 A	15 A
8 seats	Harvia 15 kW	65 A	22 A
10 seats	Harvia 18 kW	78 A	26 A
12 seats	2 x Harvia 12 kW	104 A	35 A

Current = power ÷ voltage for single-phase, and power ÷ (1.73 x voltage) per phase for three-phase. The chiller adds about 0.75 kW per horsepower while it runs: 1 HP is about 0.75 kW, 2 HP about 1.5 kW, 4 HP about 3 kW. Heaters cycle at temperature and chillers cycle at set point, but the board must still carry the worst case.

Meters, as PEA offers them

Single-phase, direct-connected: 5(15) A, 15(45) A and 30(100) A.
Three-phase, direct-connected: 15(45) A and 30(100) A.
Larger loads: CT-metered low-voltage or high-voltage service.
A new or upgraded connection is applied for at PEA, with an inspection fee; the published fee schedule dates from 1 January 2020, so confirm current fees with PEA.

A 15(45) A meter can pass up to 45 A, about 10 kW at 220⁠-⁠230 V, shared with every air-conditioner and the kitchen. An 8 kW heater on single-phase is about 35 A on its own. PEA's own consumer-safety site makes the same point for a comparable load: it says a typical home 15(45) A single-phase meter is not enough for EV charging and suggests 30(100) A single-phase or a three-phase meter. We did not find a published kilowatt threshold at which three-phase becomes mandatory, so ask the utility; our practice is to wire heaters from about 8 kW three-phase.

Interior of a glass sauna with two bench levels, a heater with a basket of stones, a bucket and ladle and a rain-washed garden outside — The heater inside the cabin is half the circuit; the other half is a breaker, an isolator and a conduit run.

Surges, storms and dips

PEA's consumer-safety pages advise surge-protected power strips and a UPS where voltage dips are frequent, and warn that lightning current can reach a home through its wiring (safesavethai.com, 2026). We found no regulation that prescribes surge protection for a sauna or chiller, so what follows is our own practice: surge protection at the incomer, a dedicated breaker and an RCD for the heater and for the chiller, an isolator beside the cabin, earthing to the electrician's drawing and a chiller controller that restarts cleanly after an interruption instead of locking out.

A condo or a hotel: ask the building

In a building the incomer and the amenity floor's distribution board are the building's, not yours. Ask the building engineer for the spare capacity on that floor, the riser's rating and whether three-phase is available there. The condo guide adds the committee side.

Questions for your utility and your electrician

What is my current meter and main breaker rating, and is the supply single-phase or three-phase?
What is the spare capacity after the air-conditioning and the kitchen are running?
If I need more, what does PEA or MEA ask for in an application, and how long does it take?
Where will the heater's and the chiller's circuits run, and can they have their own breakers, RCDs and surge protection?
Who signs the final electrical inspection on my plot?

How to photograph the meter and the board

Send two pictures. The first is the meter, close enough to read its label, for example 15(45) A, and whether it serves one phase or three. The second is the distribution board with its door open, showing the rating of the main breaker and how many spare slots remain. With those and the plot plan we can say whether the heater and the chiller fit the existing supply or whether the question for the utility has to come first. In a building, ask the manager for the same two pictures.

A worked example: a Phuket villa with a 4-seat cabin and a plunge pool

Load	kW	Single-phase 230 V	Three-phase 400 V, per phase
4-seat glass cabin heater	8	35 A	12 A
4 HP chiller while running	about 3	13 A	4 A
Pumps, UV and lighting	about 0.5	2 A	1 A
All together, if everything runs	about 11.5	50 A	17 A

On single-phase the total is about 50 A, more than a 15(45) A meter can pass and before any air-conditioning is counted. On three-phase it is about 17 A per phase, well inside even a 15(45) A three-phase meter. That is why a villa with a 4-seat cabin and a pool usually applies for a three-phase connection, or for a 30(100) A single-phase meter if three-phase is not available. The utility decides what it will connect; the layout tells you what to ask for.

Can a 4-seat sauna run on single-phase?

An 8 kW heater is about 35 A single-phase, which many home meters cannot spare. It is normally wired three-phase. A 2-seat cabin with a 4.5 kW heater, about 20 A, usually runs on single-phase.

What does it cost to upgrade a meter?

That depends on the meter and the utility's current schedule; PEA's published fee schedule dates from January 2020 and lists inspection and deposit amounts by meter size. Confirm with PEA or MEA, because fees change.

Do you need surge protection in Thailand?

We specify it. Storms are routine from May on the Andaman coast and PEA warns that lightning can enter a home through its wiring. No rule we found prescribes it, so it is our design practice.

Does the chiller need its own supply?

It needs its own breaker, and a 4 HP unit or a pair in parallel often asks for three-phase. See the chiller note.

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