Sauna / Steam Room: Complete Wiring Guide
Bill of materials
Sauna heaters are fixed electric space heating equipment under NEC Article 424. The heater is a continuous load, so the circuit must be sized at 125% of the rated current. Wire inside the sauna room must be rated for the elevated ambient temperature - standard NM-B (Romex) is not suitable inside the hot room.
Sauna heaters are continuous loads: multiply rated amps by 125% for wire and breaker sizing. Wire routing inside the sauna must use high-temperature insulation (THHN in conduit, not NM-B). Apply temperature correction factors from Table 310.15(B)(1)(1) for the elevated ambient inside the sauna room. A disconnect within sight of the heater is required per 424.19. Most sauna manufacturers specify exact wire size and breaker - follow manufacturer requirements if they exceed NEC minimums.
Small sauna heater (4.5kW)
| Component | Specification | NEC basis |
|---|---|---|
| Wire (copper) | 10 AWG THHN | Table 310.16, 110.14(C) |
| Wire (aluminum alt.) | 8 AWG THHN | Table 310.16, 110.14(C) |
| Breaker | 30A double-pole | 240.4 |
| Voltage | 240V single-phase | |
| Conduit (EMT) | 1/2" EMT | Chapter 9 Table 4 |
| Max distance (3% VD) | 153 ft at 240V copper | 210.19(A) Note 4 |
Medium sauna heater (6kW)
| Component | Specification | NEC basis |
|---|---|---|
| Wire (copper) | 8 AWG THHN | Table 310.16, 110.14(C) |
| Wire (aluminum alt.) | 6 AWG THHN | Table 310.16, 110.14(C) |
| Breaker | 40A double-pole | 240.4 |
| Voltage | 240V single-phase | |
| Conduit (EMT) | 3/4" EMT | Chapter 9 Table 4 |
| Max distance (3% VD) | 185 ft at 240V copper | 210.19(A) Note 4 |
Large sauna heater (9kW)
| Component | Specification | NEC basis |
|---|---|---|
| Wire (copper) | 6 AWG THHN | Table 310.16, 110.14(C) |
| Wire (aluminum alt.) | 4 AWG THHN | Table 310.16, 110.14(C) |
| Breaker | 50A double-pole | 240.4 |
| Voltage | 240V single-phase | |
| Conduit (EMT) | 3/4" EMT | Chapter 9 Table 4 |
| Max distance (3% VD) | 193 ft at 240V copper | 210.19(A) Note 4 |
Installation notes
GFCI is not specifically required for this application by NEC, though local amendments may differ. Check with your local building department before starting work.
For the wire run, you have two options: NM-B cable (Romex) for interior runs through framing, or individual THHN conductors in conduit for exposed runs, outdoor installations, or runs through unfinished spaces. NM-B is faster to install but cannot be used outdoors or in conduit. For conduit, use EMT (metallic) or PVC Schedule 40.
Run length matters: every foot of wire adds voltage drop, reducing power to your equipment. The table below shows the exact voltage drop at common distances. If your run exceeds the 3% threshold, upsize one gauge.
Voltage drop by distance
Percentage voltage drop at common run lengths. NEC recommends 3% maximum for branch circuits and 5% for combined feeder plus branch.
| Distance | 10 AWG Co | 8 AWG Al | 8 AWG Co |
|---|---|---|---|
| 25 ft | 0.5% | 0.5% | 0.3% |
| 50 ft | 1.0% | 1.0% | 0.6% |
| 75 ft | 1.5% | 1.5% | 0.9% |
| 100 ft | 2.0% | 2.0% | 1.2% |
| 150 ft | 2.9% | 3.0% | 1.9% |
| 200 ft | 3.9% | 4.0% | 2.5% |
Common products for 10 AWG Copper circuits
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Related wire data
Detailed ampacity: 10 AWG copper, 8 AWG aluminum. Wire size lookup: 30A circuit. Calculators: voltage drop · panel load calculator.
Frequently asked questions
What wire size do I need for sauna / steam room?
Use 10 AWG copper or 8 AWG aluminum on a 30A breaker at 240V. This is based on NEC 2023 Table 310.16 ampacity with 110.14(C) termination limits and 125% continuous load sizing per 210.19(A)(1).
Does sauna / steam room require GFCI?
No. GFCI is not required for this application.
NEC 2023 references verified April 2026