Finnmark FD-4 Trinity 2-Person Hybrid Indoor Infrared & Traditional Steam Sauna
The Finnmark FD-4 Trinity is the only home sauna engineered to deliver three distinct heat therapies in a single cabin. Combine traditional Finnish steam, full spectrum infrared, and gentle wood-heat sessions, all controlled from one app, all built into one premium thermal wood structure. It's the most versatile sauna Finnmark makes, and one of the few in the entire residential category that genuinely earns the "infra-steam" label.
Three therapies, one cabin
Most home saunas force you to pick one heat type. The FD-4 lets you switch between full spectrum infrared (near, mid, far) and traditional Harvia steam in the same session, or combine them for the full Trinity experience. Infrared penetrates deep into muscle and joint tissue. Steam opens airways and pulls heat to the skin's surface. Together they deliver something neither does alone, and the cabin handles both without compromise.
Premium thermal wood, engineered for steam
The cabin is built from premium thermal wood, a heat-treated softwood that resists moisture and won't warp under repeated heat-and-humidity cycles. Thermal modification removes resin from the wood, keeping the interior clean and inert at peak temperature. Critically for a steam-capable sauna, every joint and panel is engineered to handle the moisture loads that destroy traditional infrared cabins.
Harvia Vega heater plus full spectrum panels
The traditional steam side runs on a Harvia Vega electric heater with sauna stones, the gold standard for residential Finnish-style löyly. The infrared side uses Finnmark's full spectrum heater panels with low-EMF technology. Both systems are wired to the V2 Wi-Fi controller, so you can start any session from your phone, schedule programs, and adjust temperature without leaving the bench.
Certified, documented, and ready out of the box
The FD-4 ships with full UL listing on heating elements, ETL certification on the complete sauna system, and third-party EMF test logs you can review yourself. Finnmark publishes the documentation rather than just claiming the certifications, so you see the actual numbers, not just marketing language.
The only home sauna that combines full spectrum infrared with traditional Harvia steam in a single Trinity cabin. Premium thermal wood construction, low-EMF heaters, V2 Wi-Fi controls, and full UL/ETL/EMF documentation come standard. Built for serious wellness users who want every modality without compromise.
3-in-1 Infra-Steam sauna Full spectrum infrared Harvia Vega steam heater Low-EMF technology Premium thermal wood V2 Wi-Fi controller UL listed & ETL certified Authorized Finnmark dealer
Specifications
Dimensions & capacity
| External dimensions |
50" W × 50" D × 75" H |
| Internal dimensions |
47.2" W × 47.2" D × 71.7" H |
| Capacity |
2 persons |
| Sauna type |
Infra-Steam combination (Trinity) |
Construction & materials
| Cabin material |
Premium thermal wood |
| Glass |
Tempered safety glass door & window |
| Floor |
Reversible thermal wood floor |
| Construction |
Steam-rated joints and panels |
Infrared system
| Infrared type |
Full spectrum (near, mid, far) |
| Heater panels |
Multiple full-coverage panels |
| Max temperature |
170°F (77°C) |
| EMF rating |
Low-EMF (third-party tested) |
Steam (traditional) system
| Heater |
Harvia Vega electric |
| Heater type |
Compact wall-mounted |
| Sauna stones |
Included (Harvia) |
| Style |
Traditional Finnish löyly |
Electrical & controls
| Voltage |
240V (dedicated circuit required) |
| Controller |
V2 Wi-Fi enabled |
| App control |
Yes (iOS & Android) |
| Audio |
Built-in Bluetooth speakers |
| Lighting |
Interior LED lighting |
Certifications
| UL Listing |
Yes (sheathed heating elements) |
| ETL Certification |
Yes (Intertek infrared sauna safety) |
| EMF Test Log |
Available (PR108242) |
| Finnmark Certification |
Available |
What's included
FD-4 Trinity cabin (premium thermal wood)
Full spectrum infrared heater panels
Harvia Vega electric sauna heater
Harvia sauna stones
Tempered glass door with handle
V2 Wi-Fi-enabled control system
Interior bench seating
Reversible thermal wood floor
Built-in Bluetooth speakers
Interior LED lighting
Power supply & wiring kit
Installation hardware
Trinity installation manual
Wi-Fi controller manual
Harvia heater manual
Why the Finnmark FD-4 Trinity stands out
3-in-1 Trinity sauna
Full spectrum infrared and traditional Harvia steam in one cabin. Use either separately, or combine them for the complete Trinity experience.
Full spectrum infrared
Near, mid, and far infrared in one integrated system. Each wavelength reaches a different depth, giving you the full range of benefits per session.
Harvia Vega heater
Traditional Finnish löyly powered by the Harvia Vega, the gold standard for residential steam saunas. Sauna stones included.
Low-EMF technology
Heaters and controllers engineered to minimize electromagnetic field exposure. Independent third-party EMF test logs included.
Premium thermal wood
Heat-treated, moisture-resistant, and resin-free. Engineered specifically to handle the humidity loads from steam sessions without warping.
V2 Wi-Fi smart controller
Control infrared, steam, lighting, and audio from your phone. Schedule programs, monitor temperature, and adjust without leaving the bench.
About Finnmark Designs
Clinical-grade home wellness
The most versatile sauna Finnmark makes
The FD-4 Trinity is the flagship of the Finnmark lineup, the only model that combines full spectrum infrared with a Harvia Vega traditional steam heater in a single cabin. It's built for serious wellness users who want access to every heat modality without buying multiple saunas or compromising on the quality of either system.
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3-in-1 Infra-Steam, infrared, steam, or both at once
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Full spectrum infrared, near, mid, and far in one cabin
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Harvia Vega steam heater, with stones and traditional löyly
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Low-EMF technology, third-party tested with published logs
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UL listed & ETL certified, full safety documentation
About Finnmark Designs
Built for the home, engineered for performance
Finnmark designs every product around three priorities: heat that works at therapeutic levels, materials that last decades of daily use, and certifications that prove what's claimed. The FD-4 is the most ambitious expression of that philosophy, combining two heat technologies that normally require two separate saunas into a single cabin engineered to handle both.
From the V2 Wi-Fi controller to the third-party-tested low-EMF heaters and the published EMF test logs, Finnmark stands behind every detail with documentation. It's the rare wellness product that gives you the actual data, not just the marketing.
Manuals & Documents
Everything you need before and after installation
Download the full Finnmark Designs documentation set below. Trinity Installation & Operation Manual is the most important, review it before delivery so you know what to expect on installation day. Note that a licensed electrician is required for the heater installation, and the Harvia Vega heater has its own installation manual included.
Installation & Operation Manuals
Test Logs & Certifications
Warranty
Warranty
Finnmark Designs Limited Lifetime Warranty
Every Finnmark FD-4 Trinity is backed by Finnmark's limited lifetime warranty on the cabin's structural integrity for residential use. Heaters, electrical components, and electronics (including the V2 Wi-Fi controller and the Harvia Vega heater) are covered under their respective manufacturer warranty terms. All warranty claims go directly through Finnmark Designs with full factory support, and we are an authorized Finnmark Designs dealer. See the official warranty document above for full terms, exclusions, and claim procedures.
