When you shop for an electric sauna heater, you will see the same model offered in several voltages, most often 208V and 240V, and sometimes in single-phase and three-phase versions. Ordering the version that matches your building's electrical service is essential. This guide explains where those voltages come from, what happens if the heater and supply do not match, and how to find out what you have before you order.
Where 208V and 240V come from
In the United States, most single-family homes receive split-phase 120/240V service. Two "hot" legs each measure 120V to neutral and 240V to each other. Large household appliances such as ranges, dryers and electric sauna heaters connect across both legs for 240V.
Many commercial buildings, apartment and condominium buildings, and some mixed-use properties use three-phase 120/208V service. Each hot leg is still 120V to neutral, but because the three phases are offset from each other, the voltage between any two legs is about 208V rather than 240V.
So a 208V circuit is not a "weaker" 240V circuit. It is the normal result of a different type of electrical service. Gyms, hotels, spas, and residential units in larger buildings frequently have 208V available rather than 240V.
Why the heater has to match the supply
A sauna heater's elements are resistive. Their output depends on the voltage applied. If you connect a heater designed for 240V to a 208V supply, it will not produce its rated output. Power from a resistive element scales with the square of voltage, so the drop is significant:
(208 ÷ 240)² ≈ 0.75
In other words, a 240V-rated heater running on 208V delivers only about three-quarters of its rated power. An 8kW heater would behave like a 6kW heater. In a room sized close to the heater's rating, that can mean long warm-up times and a sauna that does not reach the temperature you expect.
The reverse mismatch, a 208V heater on a 240V supply, pushes the elements beyond their design rating. That is not an acceptable installation. Manufacturers build separate 208V and 240V versions so that each one delivers its rated output on the correct supply. Always order the version that matches your service, and follow the manufacturer's wiring instructions.
How voltage affects current draw
For a given power rating, current equals power divided by voltage. At a lower voltage, the same heater output requires more current. Manufacturer data for the 18kW Scandia Ultra heater shows the difference clearly:
- 18kW at 240V single-phase: 75 amps
- 18kW at 208V single-phase: 86.6 amps
- 18kW at 240V three-phase: 43.4 amps
- 18kW at 208V three-phase: 50 amps
Higher current means larger wire and a larger breaker. Your electrician will size the circuit according to the heater's installation instructions and local electrical code, which typically includes extra margin for loads that run for long periods. Make sure your panel has capacity for the heater before you order.
Single-phase vs three-phase
Three-phase power spreads the load across three conductors instead of two, which lowers the current on each conductor. That is why the three-phase versions above draw roughly half the amps of the single-phase versions at the same output. Three-phase service is common in commercial buildings and rare in single-family homes.
If your building has three-phase service, a three-phase heater can make wiring simpler and balance the load across the panel. If you only have single-phase service, order a single-phase model. A three-phase heater cannot be connected to single-phase power as designed.
Some large commercial installations use 480V three-phase service. Heaters built for 480V are a separate version again and are typically chosen for facilities with that service already available.
How to find out what your building has
- Check the main panel label. The panel or service equipment usually lists the voltage (for example, 120/240V or 120/208V) and the number of phases.
- Look at the main breaker and bus configuration. A three-pole main breaker generally indicates three-phase service. A two-pole main is typical of single-phase service.
- Ask your building manager or utility. In multi-unit and commercial buildings, the facilities team or utility can confirm the service type.
- Have an electrician measure it. A licensed electrician can measure voltage between legs and confirm whether 208V or 240V is available at the planned location. This is the most reliable option and is worth doing before ordering any hard-wired heater.
Which should you choose?
The answer is simple: the one that matches your supply.
- Single-family home with standard service: usually 240V single-phase.
- Apartment, condo or unit in a larger building: often 208V. Confirm before ordering.
- Commercial facility, gym or hotel: often 208V or 240V three-phase, sometimes 480V three-phase.
Once you know your voltage and phase, pick the heater size based on your room volume. Our guide to sizing a sauna heater by room cubic feet walks through the measurement process step by step.
Installation notes
Electric sauna heaters are hard-wired appliances. Installation should always be done by a licensed electrician following the manufacturer's instructions and local code. That includes wire sizing, breaker sizing, the use of high-temperature-rated wire where specified, and placement of the control panel and temperature sensor. Many heaters come with a separate control box or a thermostat mounted on the heater, so plan where controls will go before wiring.
Browse heaters by voltage
Every electric heater in our sauna heaters collection lists its voltage and phase in the title and specifications. If you are unsure which version fits your building, send us your panel information and room dimensions, and we will help you match the right model.