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Shop sauna heatersThe ThermaSol outdoor sauna lineup
The Fortis is the ThermaSol outdoor we recommend when the buyer’s first question is about winter. Most outdoor cabins are insulated to a European-standard spec that holds up in shoulder seasons. The Fortis goes further: multi-layer insulation throughout, full Thermo-Aspen framing rated for repeated cold-weather cycling, and an 8 kW Harvia Virta sized to recover quickly in single-digit weather.
Spec sheet
- Footprint: 90 by 87 inches, 89 inches tall, 403 cu ft
- Capacity: 3 to 4 adults
- Heater: 8 kW Harvia Virta with Wi-Fi; CX45 controller
- Multi-layer insulated walls; eave roofline
- Glass: dark gray front; Door: aluminum-framed glass with hidden hinges
- Exterior: thermally modified spruce; Interior: thermally modified aspen
- LED color; built in the USA by ThermaSol
Construction details
8-millimeter Parsol Dark Gray (PSDG) glazing in an aluminum frame with hidden hinges. The eave-style roofline gives a modern silhouette and a slight overhang that encapsulates the entry. Brushed Tyrol panel facade across the exterior, with thermally modified aspen for the interior framing and benches.
How it differs from the Nordic Misty
Both share the Cube line geometry, but the Fortis swaps European-standard insulation for a multi-layer wall package and a tighter eave roofline. If the placement pad sits in a zone with sustained sub-zero winters, the Fortis is the right answer.
FAQ
How many people fit?
Three to four adults.
How long does it take to heat up?
Roughly 40 to 55 minutes in cold weather.
Do I need an electrician?
Yes.
What’s the warranty?
One year manufacturer warranty.
Can it stay outside year-round?
Yes; this is the cabin engineered for that.
What’s the lead time?
Twelve weeks.
Built by Kirami in Finland
The Fortis is an additional configuration of the Kirami FinVision® production line, built at Kirami’s factory in Sastamala, Finland. The same factory builds the Nordic Misty, Nordic Dawn, and Solaris cabins for the American market, and ships their direct FinVision® counterparts to European customers. The FinVision® line carries the Finnish Key Flag Symbol (Avainlippu): the credential that certifies Finnish-designed, Finnish-manufactured, and built from Finnish materials.
Kirami’s own image archive uses the “kiramibyharvia_kir” file-naming pattern across the production line, making the supply chain visible: Sastamala-built cabin, Harvia heater, ThermaSol distribution to the American premium market. Finnish sauna culture is inscribed on UNESCO’s Representative List of the Intangible Cultural Heritage of Humanity.
Kirami joined the Harvia Group in May 2021, so the heater you choose and the cabin it sits in are now sister-company products engineered together. The integrated LED lighting wires into the Harvia Xenio control panel, which means one controller for heat, time, and ambiance.
Finnish ventilation engineering: fresh air enters through the intake on the heater side wall; spent air exhausts through the vent at the opposite upper back corner. Continuous airflow during a session without the cold drafts that plague poorly ventilated outdoor saunas.
Shipping
Free shipping included. Outdoor cabins ship fully assembled via flatbed trailer. A forklift or crane is required at delivery for placement; manual offloading is not recommended due to size and weight. A licensed electrician handles the heater hookup. We notify customers two weeks before scheduled delivery so the site is ready. The path from the truck to the placement pad must be clear and accessible. Pad should be a firm, level surface with slight drainage runoff: concrete, decking, pavers, or compacted gravel.
Optional hands-on installation
If your delivery timing aligns with our calendar, founders Ben Burger or Ben Frizzell will travel to help with the install in person. The Bens have airdropped into builds with customers across the country since launching the marketplace. This is offered for a limited time and depends on schedule availability. Ask before checkout to see whether your delivery window works.
Prebuilt
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Vents