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Authentic Sauna Blog

Building a sauna? Some electrical tips so you won’t get fried.

wiring an outdoor sauna for power and in this case speaker volume control.
wiring an outdoor sauna for power and in this case speaker volume control.

Saunatimes has a bias towards wood burning saunas and vigilantes are building the “Recycle Your Infrared Light Bulb Closet” movement.  Yet electric sauna stoves have their place.

Below is guest post from Miller Bradley, an Electrical Engineer by trade.  He, in my view, is the expert on electrical and saunas.  If you have questions/comments, please use the comment section below this post as we encourage him to chime in more:

Enter Mr. Bradley:

Here are some electrical issues to consider when planning a sauna. Sometimes a decision

can be made in the early phase of the project which seems like no big deal that may have

large ramifications later. Hopefully, this info will guide folks in the decision to go with a

wood or electric sauna heater.

Note that all requirements are based upon the National Electrical Code (NEC). Local

ordinances, foreign countries, etc. may have different requirements. When in doubt,

consult with a licensed electrician or your local building/inspection department.

Local sauna wiring (wood or electric heater)

• Circuits protected by a 20-amp circuit breaker require #12 AWG copper

conductors. 15-amp circuits can use #14 conductors but are also allowed to use

#12. It is not permissible to install #14 AWG copper conductors on a 20-amp

circuit. Important to note that all the conductors on a 20-amp circuit need to be

#12, including those for lights.

• For exterior saunas, consider installing an exterior receptacle. This is a nice

feature for plugging in power tools, a radio, etc. It can be on the side or rear of

the sauna for aesthetic purposes. Exterior receptacles need to be GFCI protected,

be of the ‘weather-resistant’ type (there will be a ‘WR’ symbol on the face of the

receptacle) and be installed with a weatherproof ‘in-use’ cover (something can be

plugged in and the cover can still be closed). If you want to put Christmas lights

or similar up on the sauna, consider an additional receptacle up near the roof edge.

• Exterior lights need to be rated for outdoor use. Simplest is a wall-mount fixture

adjacent to the door. Consideration should be given to how the fixture will be

mounted to the wall. For any siding other than totally flat, the light should be

installed on a mounting block. This is to create a flush surface for mounting the

light fixture, as opposed to the uneven surface of angled siding. This can be as

simple as a block of wood. Manufacturers also make siding mounting blocks,

both for use with vinyl siding as well as wood siding. They also make some for

retrofit applications so it is easy to install something to an existing structure.

Considerations for electric sauna heaters (exterior or interior)

• Does the service have adequate spare electrical capacity for the heater? Larger

electrical heaters are on the order of 8-10 kW and can easily be the largest

electrical load on the service, even larger than electric ovens, water heaters and

clothes dryers. Larger/newer homes with 150 or 200 amp services typically will

have adequate spare capacity for an electric sauna heater but it can be an issue

with older/smaller homes that have 100 amp services. There are some really old

homes out there with 60 amp services.

• Does the existing panel board have adequate spare physical space to accommodate

the 2-pole circuit breaker for the heater? Almost all electric heaters are 240

volt, single phase and require a 2-pole circuit breaker (similar to that for an

air conditioner or electric oven/water heater/clothes dryer). If your panel does

not have spare spaces, existing single-pole circuit breakers would need to be

converted to tandem breakers to free up space or a sub-panel may need to be

added. Also consider additional spaces for a 15 or 20-amp circuit for lights,

receptacles, etc.

Special considerations for indoor saunas with electric heater

• How will conductors get from the panelboard to the sauna? Will finished walls

need to be opened up to install wires and later be repaired? Or could the sauna be

located such that finished walls would not need to be opened?

Special considerations for detached, outdoor saunas with wood heater

• If only a single, underground circuit is brought out to the sauna for lights/

receptacles, consider GFCI protection for the entire circuit.  This doesn’t mean

a GFCI out at the sauna but rather a GFCI circuit breaker at the main panel or

serve the sauna off of the load side of a GFCI receptacle at the house. The reason

for this has to do with burial depth for the conductors from the main panel out

to the sauna. In general, direct-buried conductors need to be 24” deep but single

GFCI-protected branch circuits rated 20 amps or less only need to be 12” deep. A

heck of a lot less digging! You can also place it in a PVC conduit but would still

need to be 12” deep (or 18” deep if it is not GFCI protected). It can be as little

as 6” deep, GFCI-protected or not, if installed in rigid metal conduit but this is

a somewhat impractical installation technique for the average homeowner. And

since the entire circuit is GFCI protected, there is no need for GFCI receptacles at

the sauna; “regular” receptacles will do. Note that if there is a GFCI trip though,

you’ll have to walk back to the house to reset it!

Special considerations for detached, outdoor saunas with electric heater:

Outdoor, detached saunas with electric heaters present some special challenges. Per

the NEC, only a single circuit can be installed to serve a given detached structure. This

creates a problem as there typically needs to be at least two circuits, one for the sauna

heater and a separate circuit for lights/receptacles. If only a heater is desired with no

lights/receptacles, then the single heater circuit can be installed and all is well but if going

to the trouble of getting electricity out to the structure, makes a lot of sense to install

lights and receptacles as well. There are some heater units out there that include built-
in components for serving a single light and switch (which means only one circuit out to

the sauna) but this won’t work the best for serving additional lights in a changing room,

receptacles, etc. The best solution is to install a sub-panel at the sauna. Luckily, having

a changing room makes this a pretty easy task. So with the idea of a sub-panel in mind,

Some other issues to consider:

• Is it even feasible to install conductors underground (i.e. rocky soil, backyard is

entirely paved, etc.)?

• What route will the conductors take from the main panel to the sauna? Are there

other exterior buildings to go around? Would it make sense to locate the sauna

on one side of the house or the other, for ease of running conductors? If the main

panel is on the opposite side of the house as the sauna, is it possible to install a

portion of the circuit inside, to eliminate the need for excessive digging outside?

• Digging the trench. Can it be done by hand? Works okay if you have the time,

the run isn’t too long/deep and the soil is easy (i.e. all sand). Consider renting

a trencher from a rental place or hiring a landscape company to dig it. Be sure

to have the utility companies locate their underground lines and be aware of

anything else that may be in the way (i.e. septic tank or underground sprinkler

lines).

• Burial depths. In general, here are the minimum depths for conductors in

accordance with the NEC:

o Direct-buried: 24”

o In PVC conduit: 18”

o In rigid, metallic conduit: 6” (this is threaded, rigid pipe, not EMT)

• Wire. The feeder from the main panel to the sub panel needs to be 240 volt, 3-

wire. This includes two ungrounded conductors (hots), a neutral and a ground.

If direct-burying cable, it needs to be rated for direct-burial. UF (underground

feeder) cable is the most typical type used. If using PVC or rigid conduit,

most common choice is individual THWN conductors. The inside of a buried

conduit is considered a wet environment so conductors within the conduit must

also be rated for wet locations. If using conduit, consider sizing it larger than

the minimum required by the NEC as it makes for easier installation of the

conductors.

• Grounding electrode system. Since a feeder is being brought to a detached

structure, a new grounding electrode system must be installed at the sauna. There

are many ways to do this but the simplest is two ground rods driven into the earth

and located minimum 6’ apart. The ground rods are bonded to each other and the

ground bar in the sauna subpanel with an unspliced length of copper conductor,

typically #6 AWG.

• Subpanel. For a clean look, select a sub panel that can be flush mounted, such

that the cover is flush with the finished wall. Mount it in the changing room on

an exterior wall, ideally not above the bench. You can always hang a tapestry or

poster or similar over the face of it for aesthetics. Best to have a sub panel with a

main breaker that can turn everything off at the sauna. Sauna heater would have

its own breaker and recommend separate circuits for lights and receptacles. That

way if the heater trips or a power tool trips a receptacle, you don’t lose the lights

as well.

• Size of subpanel/feeder. This will vary depending on the size heater installed and

whether or not future capacity is desired (i.e. build a shed next to the sauna and

have a circuit run over there from the sub-panel). Typical sizes would rang from

40 amps to 70 amps.

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24 Comments on This Post

  1. Hi… Thanks for giving some tips to the people how to stay safe while building a Electric sauna heaters and how to prepare them. Really you did a great job.

  2. Hi…. The NEC recognizes rigid steel metal conduit as a grounding conductor obviating the need for a wire grounding conductor when running a circuit out to a sub-panel for example.
    Rigid typically only requires 6 inches of burial, but there are exceptions such as running under drive- ways.
    The neutral bus and the ground bus must not be electrically connected in a sub-panel.
    A conduit run is not permitted to have more than the equivalent of four (4) right angle bends. If there are more than four, then a pulling point such as a pulling elbow or a conduit body etc. must be installed in the run.
    The conduit must be completely installed before any wire is pulled into the conduit.
    All conduits have a maximum number of conductors that may be installed in them for a given conduit size. This maximum is influenced by many factors and is best looked up in conduit fill tables

  3. howard, i tried to shy away from too much discussion on rigid as it is not a material most homeowners have the tools/skills to work with. good point on number of bends in a conduit run and pull points. for anyone out there reading, be aware that such pull points need to be accessible (i.e. you can’t bury them)

    and as always, check with your municipality for any local amendments to the NEC. for example, here in wisconsin, i needed to install a second ground rod at my sauna, to supplement the first ground rod. NEC allows omitting of the second rod if the resistance to earth of the first rod is less than 25 ohms but in wisconsin, i don’t have that option, a second is required. of course, a second $10 ground rod is far cheaper than performing the resistance test but the point is wisconsin has an amendment to the ‘regular’ NEC rules.

  4. Hi there,

    I’m hoping to install LED lighting in my outdoor, electric barrel sauna. Is it possible to install a GFI receptacle inside the sauna to plug the lighting strips into? Or can I only use lighting that is hard wired?

    Thanks for your help!

  5. Mike: Here’s how i’ve handled electric with all my outdoor sauna builds.
    1. Getting electric to the site: A job is conduit and dig a trench from house/electrical box. Conduit and 110v 20 amp or 15 amp depending on anticipated draw, which should be minimal. B job is just a male end of an extension cord.
    2. GFI Outlet: Whether A or B above, this feeds into a GFI outlet into changing room. If barrel sauna with no changing room, put your GFI outside somewhere convenient and use an outside box.
    3. Wire from this another electrical box, or simply plug in your LED lighting to this outlet.
    4. After build wiring: Consider drilling a benign hole into your hot room to accept your LED lights.

    Now Mike, there’s nothing wrong with a $5.00 strand of LED Christmas lights. If you’re doing this, consider cutting off the male plug. Then you’ll need a much smaller hole drilled through your floor. Once you feed your lighting or wires, then reattach your plug and electrical tape, plug it in and you’ve got a $5.00 LED light system in your hot room.

    All these shenanigans are detailed in my Build your own sauna ebook. Including a pretty cool system for running LED lights behind your back rest or under your benches for ultra subtle vibe. Dimmer too. Hope this helps. Send pics!

  6. I have a big tree near my new sauna site which is about 15′ away from the house. This makes any reasonable digging next to impossible due to spread of the roots. I plan to install exterior 220v 40amp outlet on the outsidr of the house and use 8ga extension cord to power the sauna. Also i plan to use battery powered led lights. Will this installation be code complaint? Thanks

  7. Konstantin:

    Your question about 240v 8ga extension cord code compliance is out of my wheelhouse, sorry. My suggestion is to call 2 electricians within your area code and ask them. If you get the same answer, you’re most likely doing the right thing. Then, to sleep at night, call your building inspection department and ask them if a guy can run a 220v welder in his garage with an extension cord (legally). If he/she says yes, then you’re in a good spot. PS>. if you call the same building inspector and tell him/her that you’re building a sauna, you may be subject to lots of bullshit. Just sayin’.

  8. using portable cords as a replacement for permanent wiring is a no-no as far as the national electrical code is concerned. this is a safety issue in that cords typically lay on the ground, can be a trip hazard, are subject to additional abuse, etc. if you went to the permit office with that plan, they would more than likely give it a thumbs down.

    all that being said, there really isn’t a practical danger with a cord lying in the hard for a couple hours a couple times a week when taking sauna. the #8 conductor size would be appropriate for a 40 amp circuit. if going the permit route, go with the recep on the side of the house before you even start the sauna construction, tell the inspector it is for a welder or an rv or something like that. make sure it has a weatherproof cover and i would recommend a twist-lock receptacle to help keep the cord in place. of course, this only works if not permitting the sauna proper, as they will put two-and-two together when coming out to inspect the sauna.

    if you don’t feel like having a wad of cord on the side of you sauna when not in use, you could also put a recep at the sauna itself and unplug the cord from both ends when not in use. this would require a male receptacle at the sauna, they are available, ask an electrician.

    not sure where you are located but if in a cold climate, note that the #8 cord is going to be stiff as hell if out in the cold for very long. that’s a reason right there to have the cord plugged at both ends, so you can take it inside when not in use and keep it warm, easier to plug in. after sauna, drag the whole cord in the house as a frozen pipe, let it warm up and coil.

  9. Hi Glenn and Miller, Thanks for the comments. I was not planning to permit the sauna, but I was going to higher a licensed electrician. I’m in CA by the coast, so no concern with freezing the cord. My plan was to have the cord suspended from that before-mentioned big trip to avoid the trip hazard. I was going to route the cord up the house 8′ wall to the eve than across to the tree then across to the sauna.

    I’m still researching a longer route around the tree. I can perhaps dig at least 6″ and use EMT conduit to burry it in the walkway area and perhaps leave the EMT conduit immediately next to the tree.

  10. a code official would stroke-out over your plan but it really isn’t that big a deal. if running the cord overhead, be sure to properly support. not only to keep it from falling down but also from excessive sag or tension that could weaken the insulation over time.

    in regards to to conduit depth, you are allowed to go as shallow as 6″ in conduit but it needs to be rigid or intermediate conduit. this is the heavy, threaded stuff. EMT is technically not conduit, at least so far as the NEC is concerned. you are allowed to bury EMT but need to provide supplemental corrosion protection, to prevent the EMT from rusting through. rigid and intermediate conduit has much thicker sidewalls compared to EMT, rusting through is not as big a concern and the conduit can be buried ‘as is’.

  11. Hello- I am building a sauna in my stand alone studio building behind my house. I purchased a HomeSpa sauna heater and control from a neighbour but I am uncertain as to the correct wiring configuration. The heater is 5kW, 230 Volt, single phase, CSA approved; it has 2 elements wired to 2 terminals in the bottom of the heater. On the other side of these 2 terminals are 2 terminals which have been hand labelled in felt pen T1 and T2. The screws in the T1 and T2 terminals are backed off but no indication of what wire was connected there. Beside these 4 terminals are 2 more terminals with backed off screws but, again , no indication of what wires were connected. These last 2 terminals appear to be completely independent of the other 4. The control is a simple thermostat with a black and red wire attached at the back as well as the long, copper thermocouple wire and sensor. Beside the thermostat is the “pilot” light with two black wires with on slide-on connectors.
    The main service (200 amp) comes into the main electrical panel in the studio from the pole, then goes underground to a 100 Amp sub-panel in the house, so I have plenty of capacity in the studio. I will install a 30 Amp dedicated breaker for the sauna heater.
    I am planning to use 10/2 wire for the heater but don’t know if I should wire from the electrical panel directly to the heater and then back to the thermostat OR to the thermostat and then to heater OR one wire (black) from the electrical panel to the black thermostat wire while the other wire on the thermostat is wired to the T1 or T2 on the heater. Or if I should use 10/3 wire and take 2 load wires to the heater since there are 2 load terminals. Should the ‘pilot’ light wires be wired to the load and thermostat wires?
    There is room in the triple gang junction box to include a dimmer switch for lighting but that will be a separate circuit (15 Amp dedicated circuit) and wiring using 14/2 wire- should this be 12/2 wire?
    I am in Alberta Canada so subject to the Alberta Building Code, National Building Code of Canada and related electrical codes.
    I believe HomeSpa is no longer in business and I cannot find a heater manual online.
    Looking forward to hearing from you. Thank you.

  12. Simon, i don’t know what an electric shower is. Showers inside a sauna hot room is generally frowned upon. Sauna stoves are more subject to rust and the sauna bather is missing out on chilling out in the garden all misty wet with rain (proper cool down/ cold plunge simulation).

  13. GFCI circuits are almost always a bad idea with electric saunas. They will constantly trip if you’re splashing water on the the heater rocks and the water causes a conduction path between two elements which are operating on different phases (well, same phase, but different polarity). Not an expert but all the electric heater install manuals specifically warn against installing the heater on a GFCI or RCD (UK term) circuit. Subpanel is the best solution and add a GFCI-protected circuit there if needed, separate from the heater circuit.

  14. Hi,

    We are building a sauna in a detached garage. Within the sauna room we are hiding an HRV under one bench and a mini electric boiler and pumps under another bench. We are intending to protect the mech/elec. units with a metal pan to carry any moisture away from under these bench areas. Are you aware of any specific building code or electrical code regulations that would guide us in this application? We are building in Ontario.
    Thanks.

  15. Karin: I’m not sure. I’d contact the HRV mfr. and get their take on it. If it were me, i’d box everything in with cedar and rigid foam on the inside, with a hinged access panel, but that’s just me.

  16. Thank you for sharing the helpful information, Miller and Glenn. I am wiring an electric sauna heater (6kW) in a detached outdoor structure and am wondering about the ground rods that you recommend installing. Unfortunately I only read this after running the wiring and ended up sending two circuits out from the my main panel (a 240v and 120v), which appears to be improper for NEC guidelines. Do you still recommend installing additional grounding rods despite the fact that I do not have a new sub panel at the structure (it should be grounded through the main panel)?

  17. I can see no reference to the heat resistance capacity for the wiring. Both to the lights and the electrical stove
    Can you advise please

  18. keir: sorry, missed your comment earlier. 225.30 of the nec dictates only a single feeder or branch circuit can serve a remote building but there are exceptions, notably 225.30(D), which allows for multiple circuits for ‘different uses’. you could argue the 240v circuit is for the heater and the 120v is for lighting, hence ‘different uses’ but an inspector may not buy it. intent of the requirement is that it is easy to kill all power to a building in an emergency (i.e. fire department), without having to hunt around for multiple breakers. practically, the installation is fine with the two circuits and i wouldn’t worry about it. or the additional ground rod. it is a nec requirement if there is a panel out there (of which the benefit is questionable) but it is not a requirement for circuits.

    barry: most cable will be rated for up to 90 degree C or 194 degree F. that being said, cabling should be in the wall (not exposed in the hot room) and it will be much cooler there. even that little bit of cable that is exposed by the heater will be down near the floor where it just doesn’t get that hot. there is significant heat stratification in the hot room so while it may be 200+ degree F up by the ceiling, it may only be 90 degree F or so down at the floor, well within the temperature rating of the cable.

  19. Hi Glenn – We’re building an exterior wood-fired sauna. We made the ignorant mistake of wiring two outlets (near the floor) and a three gang switch inside the sauna. After reading about heat and moisture dangers, we need to fix this. What do you recommend? Move the switch to the exterior and remove the outlets? We also have a sauna-rated can light. How do you prevent the wiring to the can light from overheating in the hot ceiling?

  20. Laura:

    uh oh. Yes, fix this. We build our saunas one time, and get to enjoy them the rest of our lives. So we will fix this right now. Move the switch from your hot room to your changing room. Yes, pull the wires and remove the outlets in your hot room. As far as sauna rated can light, I am not a fan of lighting in hot room ceiling. I am a huge fan of LED under upper bench rope lighting. Please use search bar on saunatimes and refer to my ebook “Sauna Build, from Start to Finnish” for more details here. As far as using your can light, I’d move it to your common wall between your hot room to changing room, about 1′ below the ceiling. Your wires are protected better in the wall, through your box and within wall insulation. It’s amazing how much less hot it is on a wall vs. in the ceiling, where the heat just keeps pushing up and up and up.

    These are learning curves and it’s a good thing that you have found saunatimes as literally hundreds of others have been down the road you are traveling and we/I are all in support of you building a good sauna.

  21. Thanks for the help on the electrical questions from Laura. I removed everything as you mentioned. Since this sauna is outside and doesn’t have a changing room I had to run a 3 gang exterior box mounted on the outside wall. This 3 gang will have 3 switches inside, 2 switches’ wires run out the back of the box and into the sauna wall up to the ceiling where 1 wire will connect to a sauna rated recessed can light and 1 wire will exit out the front peak of the sauna wall for an exterior light. The 3 gang exterior box has pvc conduit running down to a 1 gang exterior box acting as the junction “power” box and also has an outlet in it. 3x THHN wires will run from the 1 gang box to the 3 gang box bringing power to the 3 gang box. The 3rd switch in the 3 gang box controls the 1 gang box’s outlet for an LED rope light that I will probably just run from the inside of the sauna into a rogue hole in the sauna wall to the exterior 1 gang box’s outlet, similar to what you mentioned. This was the best design I could think of without the convenience of an enclosed changing room. I’m running 12 ga. UF-B wire and THHN 12 ga. wire, the main power source will eventually get buried and connect to an exterior garage’s GFCI outlet so everything in the sauna should be GFCI protected. Any other thoughts or tips are definitely appreciated, thanks again for the help.

  22. Jeff:

    I couldn’t think of a better way to do what you’re doing, vis a vis electric and a hot room only outside build. Love the “rogue hole” idea as there are no rules here, and you’ve created your own solution – very effective.

    Only think I can think of is you can make an eyebrow, angled mini roof over your electrical box. It could look cool and will be functional. Just some exterior siding material fixed against a little 2×2 header against your exterior wall, on an angle, to cover your electrical box from snow and rain etc. Something along the lines of 6″ or 8″ wide by about that long, and about a 20-30 degree angle. A little flashing to pull any water running down your outside wall away from your box. Could be a nice statement piece.

  23. Yeah, the roof idea could be a good one to keep water out. I’ll need to do something similar to protect the metallic pan box I plan to mount on the exterior wall for an outside light. There is not a big overhang, so it will be quite exposed.

    Sweet, yeah, I didn’t know if the rogue hole was legit, but seems easy and keeps everything outside except for the rope light.

    For the 3 gang box’s knock out on the backside, going into the sauna wall, I’ll simply use a standard nm cable clamp and some duct seal around it. I can’t think of a better way of doing this.

    The inside recessed light I am hoping to keep in my design as it is more of a utility light to turn on when you need to see inside the sauna. The rope light will be more of a light when actually using the sauna. I’ll try and insulate the roof as much as possible to keep the wire cool I guess.

    Thanks again for the help Glenn. If you think of anything else, let me know!

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