Sauna: Electrical rough-in

Posted by thom October 10, 2026

Sauna: Electrical rough-in

Not a small step: the electrical rough-in for our sauna passed inspection.

Now we can move onto the next phase of the project... finishing the landscaping, which includes building a small retaining wall, leveling a third of our yard, and building custom concrete pavers which will serve as the sauna's foundation.

Something I've enjoyed about projects in this house is they bring a new challenge. Despite having done a LOT of electrical over the years, including running new branch circuits for the kitchen and for a washer/dryer, I've never run a new circuit outside. Meaning I'd get to learn a bunch of stuff.

Specifically then, what I needed to do involved running new 220v (for the Harvia 6kW heater) and 110v (for the interior and potential exterior lighting) branch circuits. Our service panels are in our garage, about 75' from the sauna.

To get power from the panel to the sauna, I designed the raceway:

3/4" EMT conduit along the garage ceiling, with 3/4" FMC conduit on either end to make the connection to the panel and to the PVC easier (read: not having to bend the EMT)
3/4" schedule 40 PVC conduit outside
#10 THWN-2 stranded conductors (2) and shared ground
#12 THWN-2 stranded conductor and neutral
30A non-fused kill switch within line of sight of the sauna (the heater, specifically)
30A dual-pole GFCI breaker (despite Harvia stating not to use a GFCI breaker in their installation instructions, US electrical code requires one) and 20A single-pole breaker
All of the various connectors to transition between the different conduits, as well as conform to electrical code (including, but not limited to not more than 40% of the diameter of conduit being filled by conductors and no more 360º of bends for any single pull)

I spent a lot of time researching and chatting with GPT. At some point, I asked it how much this project would cost if K and I kicked up our feet with a beer and watched other people do it for us. The answer: an easy $3k, maybe $4k. Not only do I enjoy learning and doing this stuff, but that means our sauna doesn't cost that much more to actually experience löyly.

Getting to the installation, part of my research involved where to drill through our house to get current from inside the garage outside to the sauna. I never take it lightly putting a hole in our home, so I went back and forth drilling a 1-1/4" hole through the wood header that spans the garage doors or through the hollow cinder block that makes up our garage foundation walls. In the end, I went with the concrete block. I just wasn't convinced it was smart to drill through a header.

I then finished the metal raceway in the garage.

Before finalizing the transition from FMC to schedule 40, I pieced it together.

There are couplers and transitions for everything. In this case, the raceway went from PVC to a very short length of EMT to a short length of FMC back to the rest of the garage raceway, EMT.

Outside, I dug first dug a trench 18" below the surface.

The raceway would pop out of the garage a few feet from the deck, run underneath the deck framing then drop down into the trench. I'd branch the two #10 conductors and #10 ground off to the kill switch attached to the deck fascia. Most importantly, the PVC conduit would come up on the left side of the sauna. Sitting on the deck, this is the side we will really never see. Basically, I wanted to avoid something like this that K found on Reddit, heh...

Yeah, I'm not sure what's up with that. The owner definitely got some flack from the Redditors. For our installation, the schedule 40 will come up tight against the unseen left side of the sauna right where the wall goes vertical. I'll then run a length of 1/2" LFMC conduit under the sauna to the other side, popping up in the floor directly underneath the heater, and another length (also under the sauna) to the back where the electrical box will go to connect the plug for the interior lights.

With the outside raceway designed, it was time to measure, cut, and glue all the PVC pieces together. I used blank 4x4x2 junction boxes ("JB" for short) so I could put holes where I needed them. Also, my trusty miter box and hand saw.

While I worked in the garage, I often had a helper (who herself had an audience).

Once the raceway was complete, it was time to (yay!) pull some conductors. I did pick up a bottle of Klein cable pulling lube. It came in handy, I'm not gonna lie. Also, it took both K and I to tackle this part of the job: one of us pulling and one of us feeding. I also used a dowel to hold the five spools of cable.

The raceway was essentially three separate pulls:

Inside garage EMT to PVC JB on the outside of the garage
PVC JB to JB/kill switch
JB to sauna stubout

All things considered, pulling the cables went fine. We started at the panel and pulled toward the stubout.

With the cables pulled, it was time to shut off the panel and get the two new circuits wired to their respective breakers. Part of my research with GPT was to do a load calculation for the intended panel. Despite it having plenty of available breaker slots, I wanted to make sure I wasn't going to overload it. Bottom line: I wasn't.

As I always say, wiring up the breakers is the easiest part of an electrical service and not to be taken lightly! Maybe the trickiest part of this install was to make sure I didn't screw up the concentric knockout for the 3/4" 90º FMC elbow I was connecting to the panel. It's a little surgical to get the second circle taken out. I was delicate with it because I didn't want to end up with a 1" hole!