Key facts
- A resistive heater's output scales with voltage squared. (208 / 240) squared is about 0.751, so a 240V heater makes about 75 percent of its rated heat on 208V. Current scales with voltage, so it draws about 87 percent of its rated amps.
- HUUM's DROP manual lists both: DROP 9 is 9 kW, 37.5 A on a 50 A breaker with 8 AWG at 240V, and 6.75 kW, 32.44 A on a 40 A breaker with 8 AWG at 208V.
- Harvia sells separate 208V 3-phase versions: the KIP 80 is 8 kW and 33.3 A at 240V single-phase (KIP-80-B1) or 8 kW and 22.2 A at 208V 3-phase (KIP-80-B3).
- Harvia's CX170 control unit comes in 240V single-phase versions and 208V 3-phase versions (CX170-U3), with a 10.5 kW maximum load on the U3.
- PPL Electric's service rules: in its 208Y areas, residential buildings with three or more dwelling units get 120/208 volt sub-services to each unit.
Sources: HUUM DROP installation manual tables (copy hosted by ManualsPro); Harvia KIP owner's manual (dealer-hosted PDF); Harvia CX170 control unit manual (dealer-hosted PDF); PPL Electric REMSI Rule 2; and the American Society of Home Inspectors, Let's Talk Three-Phase. Checked October 24, 2026.
Why 208V exists and who has it
Most single-family homes in the United States get 120/240V single-phase service: two hot legs 180 degrees apart, 240 volts between them. Larger buildings are often fed by a three-phase 208Y/120 volt system instead. The American Society of Home Inspectors describes it: 208 volts between any two line conductors and 120 volts from any line conductor to neutral. Each apartment gets two of the three legs, which still gives 120V for outlets and lights, but only 208V between the two hots because the legs are 120 degrees apart, not 180.
PPL Electric's service rules show how a utility handles it in practice. In areas where its secondary system is 208Y, buildings with three or more dwelling units get a three-phase service, and each unit gets a single-phase, 3-wire 120/208 volt sub-service. Utilities differ, but the pattern is common: apartments, condos, townhome rows on a shared service, live-work units and commercial spaces are the places to check. Detached houses are usually 240V, though not always.
What you lose on 208V
A sauna heater element is a resistor. Power equals voltage squared divided by resistance, so dropping from 240V to 208V cuts power to (208/240) squared, about 75 percent. Current equals voltage divided by resistance, so amps fall to about 87 percent. The table applies that arithmetic to common heater sizes. HUUM's published DROP figures, shown in the last column, match it.
| Rated at 240V | Amps at 240V | Output at 208V (calculated) | Amps at 208V (calculated) | HUUM DROP published 208V |
|---|---|---|---|---|
| 4.5 kW | 18.75 A | About 3.4 kW | About 16.2 A | DROP 4: 3.4 kW, 16.35 A |
| 6 kW | 25 A | About 4.5 kW | About 21.7 A | DROP 6: 4.5 kW, 21.63 A |
| 7.5 kW | 31.25 A | About 5.6 kW | About 27.1 A | DROP 7: 5.6 kW, 26.92 A |
| 8 kW | 33.3 A | About 6.0 kW | About 28.9 A | n/a |
| 9 kW | 37.5 A | About 6.75 kW | About 32.5 A | DROP 9: 6.75 kW, 32.44 A |
| 10.5 kW | 43.75 A | About 7.9 kW | About 37.9 A | n/a |
The calculated rows assume a heater whose maker allows 208V use. Breaker and wire sizes must come from the maker's table for your model and your electrician's application of the code, not from this table.
Room size shrinks with the voltage
Less power means a smaller room the heater can bring up to temperature in a reasonable time. HUUM's two DROP tables make this concrete:
| Model | Room at 240V | Room at 208V | Breaker at 240V / 208V |
|---|---|---|---|
| DROP 4 | 106 to 247 cu ft | 88 to 194 cu ft | 30 A / 20 A |
| DROP 6 | 177 to 353 cu ft | 141 to 282 cu ft | 30 A / 30 A |
| DROP 7 | 247 to 424 cu ft | 176 to 317 cu ft | 40 A / 30 A |
| DROP 9 | 282 to 530 cu ft | 211 to 388 cu ft | 50 A / 40 A |
HUUM also says to add 53 cubic feet for each square meter of uninsulated brick, tile, glass or log wall. A room with a glass door and front, which is common in condo builds, can push you up a size on 208V even if it fit at 240V. To work out your room's volume and the rule for glass and masonry, see our heater size by cubic feet guide.
Single-phase 208V vs 3-phase 208V heaters
These are not the same thing, and the labels confuse buyers. A heater like HUUM's DROP connects across two hot legs whether they are 240V apart or 208V apart; it just makes less heat on 208V. A 3-phase heater, such as Harvia's KIP B3 and W3 models, is built for three hot legs and spreads the load across them, which is why Harvia lists the 8 kW KIP 80 at only 22.2 amps on 208V 3-phase. Harvia's CX170 control unit likewise comes in U1 (240V single-phase) and U3 (208V 3-phase) versions. An apartment with a two-leg 120/208 sub-service cannot run a 3-phase heater. Commercial spaces with a three-phase panel can.
How to plan a sauna in a 208V building
- Confirm the service. Panel labels, the building's electrical drawings or the property manager will say 120/208 or 208Y/120 if that is what you have. An electrician can measure it.
- Confirm the building allows it. Condo and co-op boards often require approval for new 240V or 208V circuits and for a room that adds heat and moisture. Get that before you buy.
- Pick a heater whose manual lists 208V operation, and size it from the 208V room table, not the 240V one.
- Check panel capacity. A sauna is one of the largest loads in a home. Our panel capacity guide walks through the NEC load calculation an electrician will use.
- Wire to the maker's 208V table. HUUM, for example, recommends connecting the DROP without an RCD (ground-fault device), and Harvia's Spirit manual says not to feed that heater through a GFCI. Follow your heater's manual and your inspector.
- Expect slower heat-up. Plan sessions with a longer preheat, keep the door closed, and use a heater near the top of what the 208V table allows for your room.
What about the saunas we sell?
Every traditional sauna in our catalog right now ships with a heater specified at 240V, for example Almost Heaven's 8 kW heaters at 240V on a 40 amp requirement and its 6 kW heaters on a 30 amp requirement. The spec sheets we checked do not list 208V output. If your home is on 208V, ask us before ordering and we will get the maker's answer in writing for the exact model.
Related guides
- What size breaker and wire does a sauna heater need?
- Sauna heater size by cubic feet
- Can one panel run a sauna and a cold plunge?
- How much a home sauna costs to run
- The best indoor saunas of 2026
Frequently asked questions
Will a 240V sauna heater work on 208V?
It will heat, but at about 75 percent of its rated output, because a resistive heater's power falls with the square of the voltage. HUUM publishes this directly: its DROP 9 is 9 kW at 240V and 6.75 kW at 208V. Only connect a heater at 208V if its manual lists 208V operation or the maker confirms it in writing.
How do I know if my home has 208V instead of 240V?
Look at the panel label or the service paperwork for "120/208" or "208Y/120". PPL Electric's service rules, for example, say residential buildings with three or more units in its 208Y areas get 120/208 volt sub-services. A licensed electrician can confirm by measuring between the two hot legs. If you live in an apartment, condo or mixed-use building, ask before you order.
Do I need a bigger breaker for a heater on 208V?
No, the current drops a little at 208V. HUUM lists 37.5 amps on a 50 amp breaker for the DROP 9 at 240V and 32.44 amps on a 40 amp breaker at 208V. Use the maker's 208V table for your model; do not guess.
Should I buy a bigger heater to make up for 208V?
That is how makers handle it. HUUM's 208V table shrinks the recommended room size for each heater, so you pick the model whose 208V range covers your room. For a room near the top of a heater's 240V range, the next size up is usually the right 208V choice, as long as the room and wiring are within that model's limits.
What is a 208V 3-phase sauna heater?
A heater built for three-phase commercial power, such as Harvia's KIP B3 and W3 models. Harvia lists the KIP 80 at 8 kW on 208V 3-phase at 22.2 amps, versus 33.3 amps on 240V single-phase. Homes and apartments almost never have three-phase power at the unit, so a 3-phase heater is not a fix for a 208V apartment.
Does 208V make a sauna take longer to heat?
Yes. With about three quarters of the power doing the same job, a room will take noticeably longer to reach temperature than it did at 240V, and longer still if the room is near the top of the heater's size range or has glass or masonry walls. Maker heat-up times assume the rated voltage.
Do Almost Heaven saunas run on 208V?
Almost Heaven lists its heaters at 240V (for example, 8 kW at 240V on a 40 amp requirement). Its spec sheets that we checked do not list 208V output. Ask the maker before buying for a 208V building.
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