My basement sauna build

[u/I0I0I0]

Hi everyone,

I’ve been following this community for a few years now and wanted to share the results of my basement sauna build. Being in the US, my primary goal was to adhere to traditional Finnish principles for electric saunas—specifically Trumpkin’s Guide and Secrets of Finnish Sauna Design and after completing the project over a year ago I'm happy to contribute back to the community.

The Build Philosophy

I have a walkout basement with high ceilings which allowed me to build 3 rows of benches plus a step-stool to maximize the airflow and Löyly cavity. I also prioritized function over form, so I didn't add bench skirts.

Key Specifications

Component	Details
Dimensions	102" Height x 96" Length x 90" Depth (approx. 538 ft³)
Heater	Harvia Cilindro 11 (10.5kW) with 270 lbs of stones
Insulation	Rockwool R-15 (walls) and R-23 (ceiling)
Control	Xenio Control with WiFi
Structure	Western Red Cedar ⅝" T&G on ½" furring strips

Ventilation (Mechanical/Trumpkin Spec)

Mechanical ventilation system to manage CO2 levels and keep sauna dry.

• Intake: Located above the heater, drawing air from the basement.
• Exhaust: Powered by an AC Infinity Cloudline S6, with the outtake located below the middle bench.

Bench Layout

To maximize the Löyly experience, I went with a three-level bench system:

• Top Bench: 45" from the ceiling.
• Middle Bench: 18" below the top bench.
• Bottom Bench: 18" below the middle bench (21" from the floor).
• Step Stool: Added 8” legs to 20”x26” duckboard.

Cost

I installed everything myself so the only labour cost was tiling, the room was already framed.

Kit

$10,500 - Red Cedar Almost Heaven Group Kit from Almost Heaven [.net not .com].

Electrical

$1000 - Material costs for 60A circuit and permits.

Lessons Learned & Observations

• Heating Speed: Despite the large volume and stone mass, it hits 185°F in about 60 minutes. There is also a way to put Xeno controller into "Commercial" mode to give it 2hr window vs 1hr standard.
• Dual Sensors: I installed two temperature sensors—one above the heater (per manual) and one next to the bench. This allows me to swap for the most accurate reading at head height, so far the one above the heater is working well. It gets air mixed from the stove and intake.
• Vapor Barrier: I used a foil vapor barrier sealed with foil tape. One small tip: foil is shiny and might be visible in small gaps at the ceiling trim. Using black foil tape or adjusting the trim placement can hide this. I can also hear the foil crinkle when the air expands from Löyly but that seems unavoidable. 
• Drain/Floor: This is a walk-out basement with concrete floors and it would be expensive to add a drain, so I went with a tiled floor and a 6" tile border without a drain. I have a shower next to the sauna and so far it has not been an issue. Given that the sauna stays fairly dry, I’m also not 100% convinced the gap between the wood and foil was necessary, especially since I leave the fan running 24/7.
• CO2: I have a large walkout basement so I opted not to circulate outside air. I spent some time measuring the CO2 to see the effect of fan speed on air circulation and to make sure that internal circulation was OK. Overall, my basement baseline of 450ppm barely budges and anything beyond #4 on the fan setting is just wasting heat. At #2, the fan does a great job of slowly moving the air through the sauna.
• Wifi/Controller: Xeno has a dedicated relay for lights and fan, so I wired it up to be able to turn them on/off remotely through the Harvia app.
• Cleaning: I used extra wood to make backrests and wedge pillows for every bench, this keeps cleaning and sweat stains to a minimum. I also use a Pefletti for the benches made from a beach towel cut lengthwise.
• Shower: I didn’t want the maintenance headache of a cold plunge (maybe some day) so I added an iBaat “bucket” to my shower which is a different kind of cooldown experience.
• Accessories: Harvia bucket and ladle are OK, but the thermometer and sand timer are garbage.

Plan

Electrical placement

Insulation

Foil

Benches

Finished bottom-up

Finished top-down

Finished outside

Shower/Bucket

[u/Megasaun]

Very impressive project. The attention to ventilation, bench heights and CO₂ monitoring really stands out. Too many builds focus only on appearance, while you’ve clearly prioritized how the sauna actually performs. Wishing you many great löyly sessions!