If you're installing a traditional electric sauna, one of the most important—and most misunderstood—parts of the process is getting your electrical wiring right. Specifically, understanding the difference between 240V and 208V power and how it affects your sauna heater's performance. Get this wrong, and you could end up with a sauna that takes forever to heat up, doesn't reach full temperature, or worse—trips breakers and creates safety hazards.
This guide breaks down everything you need to know about 240V vs 208V sauna wiring, including what these voltages mean, where each one is found, how they impact heater performance, and what to tell your electrician before they pull a single wire.
What Do 240V and 208V Actually Mean?
Before diving into sauna-specific applications, it helps to understand what these numbers represent. In North America, electrical power is delivered to buildings in two main configurations, and the voltage you have access to depends entirely on where your sauna is being installed.
240V — Standard Residential Power
Most single-family homes in the United States and Canada receive single-phase 240V power from the utility company. This is the same type of circuit that powers your clothes dryer, electric range, or central air conditioner. Your electrical panel splits this incoming power into two 120V "legs." When both legs are combined on a single circuit, you get 240V.
If you're installing a sauna in your home—whether in the basement, garage, bathroom, or a dedicated outdoor sauna building—you almost certainly have 240V available at your electrical panel. This is the voltage that virtually all residential electric sauna heaters are designed and rated to operate on.
208V — Commercial Three-Phase Power
Commercial buildings, apartment complexes, condominiums, gyms, hotels, spas, and some multi-unit residential buildings receive three-phase power from the utility. When you pull two legs from a three-phase system, you get 208V—not 240V. This is a fundamental difference in how the power is generated and distributed, and it's not something you can change without a transformer.
The distinction matters because the voltage directly affects how much power your heater can actually produce. A heater rated for 240V that's connected to 208V will not perform to its full specifications.
Why the Voltage Difference Matters for Your Sauna Heater
Electric sauna heaters are essentially large resistive heating elements. The power they produce follows a simple electrical formula: Power = Voltage² ÷ Resistance. When the voltage drops, the power output drops disproportionately—not by the same percentage as the voltage reduction, but by a larger amount.
Here's the math that matters. A heater rated at 9kW on 240V will only produce approximately 6.75kW when connected to 208V. That's roughly a 25% reduction in heating power from just a 13% drop in voltage. For a practical example, consider what that means for your sauna experience:
On 240V, a properly sized heater in an insulated sauna room might reach 185°F in 30–40 minutes. That same heater on 208V could take 50–60 minutes or more to reach the same temperature—and in rooms with poor insulation, exposed concrete, glass doors, or high ceilings, it may never reach your target temperature at all.
This is why understanding your available voltage before purchasing a heater is critical. If you're building out a home sauna and aren't sure what voltage you have, your electrician can verify this in seconds at your electrical panel.
How to Determine Whether You Have 240V or 208V
The easiest way to find out is to have a licensed electrician measure the voltage at your electrical panel with a multimeter. But there are some reliable indicators before you even call anyone.
You Likely Have 240V If:
You live in a single-family home, townhouse, or duplex. Your electrical panel has a single-phase configuration (two main breaker handles tied together). You already have 240V appliances running—electric dryer, electric range, central AC, or an electric water heater. Most standalone residential structures in the U.S. and Canada receive single-phase 240V service.
You Likely Have 208V If:
You live in a condo, apartment, or loft in a multi-story building. Your building has a commercial electrical service. You're installing a sauna in a gym, spa, hotel, office building, or commercial wellness center. Your electrical panel shows three-phase breakers or has three main incoming conductors plus neutral.
When in doubt, don't guess. Use our Sauna Heater Electrician Database to find a licensed professional near you who has experience with sauna installations and can verify your voltage.
Sauna Heater Ratings: What the Specs Actually Tell You
When you look at the specifications for heaters from brands like Harvia, HUUM, or Saunum, you'll typically see the kilowatt (kW) rating listed at 240V. This is the maximum output the heater can achieve under ideal voltage conditions. Some manufacturers also list the 208V output separately, but many don't—which is where confusion starts.
Here's a quick reference for common heater sizes showing the actual output at each voltage:
A 4.5kW heater rated at 240V produces approximately 3.4kW at 208V. A 6kW heater drops to about 4.5kW. An 8kW heater drops to roughly 6kW. A 9kW heater produces approximately 6.75kW at 208V. And a 10.5kW heater—often the largest residential option—drops to about 7.9kW when connected to 208V power.
The takeaway is consistent: expect about 25% less heating power at 208V. This doesn't mean you can't use these heaters on 208V, but it absolutely affects which size heater you need and how your sauna will perform. Our Sauna Heater Sizing Calculator can help you determine the right kW rating for your room based on its dimensions and construction materials.
Installing a Sauna Heater on 208V: What You Need to Know
If you've confirmed that your building has 208V power, you have several options to ensure your sauna performs well.
Option 1: Oversize the Heater
The most common and practical solution is to select a heater with a higher kW rating than you'd normally need for your room size. Since you're losing roughly 25% of the heater's output, choosing the next size up (or two sizes up for larger rooms) compensates for the voltage difference. For example, if your room would normally require a 6kW heater on 240V, select an 8kW model instead. The 8kW heater at 208V will produce approximately 6kW—right where you need to be.
This is the approach most commercial sauna installers use for gyms, spas, and hotel saunas. It's straightforward, doesn't require any additional equipment, and works reliably. Just make sure the heater is physically compatible with your room size—an oversized heater in a very small room can create safety concerns, so check the manufacturer's minimum room size specifications.
Option 2: Install a Step-Up Transformer
A step-up transformer converts 208V to 240V before the power reaches your heater. This allows the heater to operate at its full rated output without oversizing. Transformers are a clean solution, but they add cost ($300–$800+ depending on the kW capacity), take up physical space near your electrical panel, and require professional installation.
This option makes sense when you want exact heater performance, when the room is borderline for the next size up, or when you're installing a premium heater and want it operating at peak specifications.
Option 3: Choose a 208V-Rated Heater
Some manufacturers offer heater models specifically rated for 208V operation. These units are designed with different heating element resistances that produce their rated output at 208V. Harvia and several other commercial-focused brands offer 208V variants of their popular models. If you're outfitting a commercial space, ask us about 208V-specific models—we can help you source the right unit.
Wiring Requirements: 240V vs 208V Circuits
Regardless of whether you're working with 240V or 208V, the wiring for a sauna heater circuit must meet NEC (National Electrical Code) standards and any local code requirements. Here's what your electrician needs to know.
Wire Sizing
Wire gauge is determined by the amperage of the circuit, not the voltage. For most residential sauna heaters in the 4.5kW to 9kW range on 240V, you're looking at 30 to 50 amp circuits using #10 AWG to #6 AWG copper wire, depending on the heater size and the distance from your electrical panel to the sauna. Longer wire runs require upsizing the wire gauge to compensate for voltage drop—something your electrician should calculate.
On a 208V circuit, the amperage draw is actually slightly higher for the same wattage output because the lower voltage means more current is needed. Your electrician should size the wire and breaker based on the heater's actual amperage rating at 208V, not at 240V.
Dedicated Circuit
Every sauna heater requires a dedicated circuit—meaning nothing else is connected to that breaker. No shared outlets, no lighting circuits, no other appliances. This is both a code requirement and a safety necessity. Sauna heaters draw significant continuous loads, and sharing a circuit can cause overheating, voltage drops, and tripped breakers.
Disconnect Switch
Most building codes require a visible disconnect switch within sight of the sauna heater. This is a safety feature that allows you to completely cut power to the heater without going back to the electrical panel. Your electrician should install this as part of the heater circuit.
120V Sauna Heaters: A Different Category Entirely
It's worth noting that the 240V vs 208V discussion applies specifically to traditional electric sauna heaters—the type that heat rocks and can bring a room to 185°F+. There's a completely separate category of sauna heating that operates on standard 120V household circuits.
Infrared saunas typically run on 120V/15A or 120V/20A circuits, meaning they plug into a regular household outlet (though a dedicated circuit is still recommended). If you're considering infrared technology, the 240V vs 208V question is mostly irrelevant to you. However, larger infrared panel setups—particularly those with 7 or more panels—do require 240V circuits. Our 120V infrared heater panel packages cover rooms up to 120 cubic feet on a standard household circuit, while our 240V infrared panel packages handle larger spaces up to 280 cubic feet.
Similarly, some smaller plug-and-play traditional heaters exist in the 120V space, but they're limited to very small sauna rooms (under 90 cubic feet) and shouldn't be confused with the 240V heaters designed for standard-size saunas.
Common Mistakes to Avoid
Assuming Your Condo Has 240V
This is the most frequent and costly mistake we see. A customer in a high-rise condo orders a sauna heater, hires an electrician, and discovers during installation that the building only has 208V three-phase power. Now they either need a different heater, a step-up transformer, or they accept reduced performance. Always verify your voltage before purchasing.
Undersizing Wire for Long Runs
If your electrical panel is far from your sauna location—common with outdoor saunas or detached buildings—voltage drop over long wire runs becomes a real concern. A 240V circuit can drop to 230V or lower by the time it reaches a heater 100+ feet away, reducing performance. Your electrician should calculate voltage drop and upsize the wire accordingly.
Using the Wrong Breaker Size
The breaker must match the heater's requirements—not bigger, not smaller. An oversized breaker won't trip during an overload, creating a fire hazard. An undersized breaker will trip during normal operation. Check the heater's installation manual for the exact breaker specification.
Skipping the Permit
In most jurisdictions, adding a 240V circuit requires an electrical permit and inspection. Skipping this step can void your homeowner's insurance, create issues when selling your home, and potentially expose you to liability if something goes wrong. The permit process also ensures the work meets code—it's there to protect you.
DIY Electrical Work
We can't stress this enough: 240V electrical work should always be performed by a licensed electrician. The voltages involved in sauna heater installation are lethal. Even if you're comfortable with basic home wiring, the combination of high amperage, continuous load ratings, and building code requirements makes this a job for a professional. Use our Electrician Database to find qualified pros in your area.
What to Tell Your Electrician
When you hire an electrician for your sauna installation, providing clear information upfront saves time, prevents mistakes, and ensures the job is done right the first time. Here's what they need to know.
Give them the heater's make and model, along with the kW rating and the voltage requirement (240V or 208V). Provide the amperage rating from the heater's spec sheet. Show them where you want the sauna located and measure the distance from the electrical panel to that location. Let them know about the disconnect switch requirement and ask them to check whether GFCI protection is required by your local code.
If you haven't purchased a heater yet, that's actually ideal. Have the electrician verify your available voltage first, then use that information to select the right heater. Our team at Haven Of Heat can help you choose the correct heater once you know your voltage—just call us at 360-233-2867 or email info@havenofheat.com with your voltage, room dimensions, and construction details.
Special Considerations for Commercial Sauna Installations
If you're installing a sauna in a commercial setting—gym, spa, hotel, wellness center, or co-working space—the 208V question is almost always relevant. Commercial buildings overwhelmingly use three-phase power, which means 208V is what you have to work with.
For commercial installations, we recommend working with us directly to spec the right equipment. Commercial saunas have additional requirements beyond just voltage: higher-duty heater construction for heavy daily use, commercial-grade controls, ADA compliance considerations, and ventilation requirements that differ from residential installations. Browse our full range of electric sauna heaters or contact us for commercial project consultation.
Frequently Asked Questions
Can I convert 208V to 240V?
Yes, with a step-up transformer. This is a common solution in commercial settings. The transformer must be rated for the continuous wattage of your heater plus a safety margin. Professional installation is required.
Will a 240V heater work on 208V?
Yes, it will work—but at reduced output (approximately 75% of rated power). The heater won't be damaged, but it will heat more slowly and may not reach desired temperatures in larger or poorly insulated rooms. Most manufacturers explicitly state in their manuals that their heaters can operate on both 208V and 240V.
What if my voltage reads 230V or 235V?
That's normal for residential 240V service. Utility voltage fluctuates slightly, and anything in the 230V–250V range is considered standard residential voltage. Your heater will perform within its rated specifications at these voltages.
Do I need different wire for 208V vs 240V?
The wire type is the same (typically THHN copper in conduit or NM-B/Romex for residential), but the gauge may differ. At 208V, the heater draws slightly more amperage for the same wattage, which could require a heavier gauge wire. Your electrician should size the wire based on the actual amperage at 208V, not the 240V rating.
Can I use my existing dryer outlet for a sauna heater?
Generally no. Most dryer outlets are 30-amp NEMA 14-30 configurations, while sauna heaters often require 40-amp or 50-amp circuits with different connector types. Additionally, sauna heaters must be hardwired—not plugged in—per most building codes and manufacturer requirements. The existing wire gauge from a dryer circuit may also be insufficient for larger heaters.
What about 220V? Is that the same as 240V?
In common usage, yes. People often say "220V" when they mean 240V—it's an older designation. Modern North American residential standard is 240V (with typical actual measurements between 230V–250V). When someone says they have "220V" at home, they have 240V service. The important distinction is between this residential single-phase power and commercial 208V three-phase power.
Choosing the Right Heater for Your Voltage
Understanding your voltage is the first step. The second is selecting a heater that will deliver the sauna experience you want. Whether you have 240V residential power and need a perfectly sized heater, or you're working with 208V commercial power and need to plan accordingly, getting the right match between your electrical supply and your heater is non-negotiable.
Start with our Sauna Heater Sizing Calculator to determine the right kW rating for your room. If you're working with 208V, use the calculator's recommendation as a starting point and size up by approximately 25–30% to compensate. Then browse our electric sauna heater collection from brands like Harvia, HUUM, and Saunum to find the model that fits your space, your style, and your budget.
Not sure where to start? Our Oregon-based team lives and breathes saunas. Call us at 360-233-2867 or email info@havenofheat.com with your room dimensions, voltage, and any questions. We'll help you get the wiring right the first time so you can focus on what actually matters—enjoying your sauna.
*Haven Of Heat and its affiliates do not provide medical, legal, electrical, building, financial, or professional advice. The information provided is for educational purposes only. Always hire a licensed electrician for sauna heater wiring. Consult with your local building department regarding permit and code requirements. Individual installations may vary based on local codes and building conditions.*
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