US Building Code Lets Masonry Heaters Skip the UL Listing. Wood Sauna Stoves Can't.

Christer Lybäck fires his sauna heater in the yard. When the stones are hot he pulls the embers out of the firebox, throws off the carbon monoxide steam, lays a fire blanket over the top, opens a sliding door and rolls 3,300 pounds of soapstone into the building on rails. The heater settles into a brick-lined bay, the blanket comes off, and ten people bathe in a smoke sauna that has never had a fire inside it.

The surgeon built the thing to solve one problem. Smoke saunas burn down, and keeping the fire outdoors means no spark ever reaches the timber. Sauna-lehti, the Finnish Sauna Society's quarterly, reported it this summer and called it a one-off unique in Finland.

Build it in the United States and you have an appliance no American standard describes, in a category American code has never written a rule for, facing a barrier that as far as we can tell nobody has ever asked a building official to rule on.

What he built

Lybäck is an orthopedic surgeon in Espoo. The building is a prefabricated log kit from Kontio; he built the benches himself and they seat ten, over a slatted floor for ventilation, with a dock and an ice-hole pump outside for winter swimming. First löyly was May 2026.

The heater is a Tulikivi soapstone unit carrying 660 pounds of stones, about 3,300 pounds loaded, and the rails make it light enough for one adult to move. He took the idea from a friend who had built one and pushed it further. His worry was that the stones would give up their heat once the fire was gone. There was still löyly the next morning.

One detail he mentions in passing is the one a commercial operator should notice first: the interior stays clean, because the smoke never gets in. Soot on every surface is a large part of why smoke saunas do not scale as a paid amenity.

American code recognizes two kinds of sauna heater, and wood is not one

UL 60335-2-53, the sauna heater standard ANSI-approved on June 27, 2025, covers "electric sauna heating appliances and infrared emitting units," per the scope of the IEC standard it adopts. We covered what it changed for electric heaters in April. It has no solid-fuel provision at all.

The codes that name saunas name only electric and gas. IRC M1902.2 says sauna heaters "shall comply with UL 875," an electric-only standard, while M1902.3 immediately provides combustion air and venting for fuel-burning saunas. IMC Section 914 manages the contradiction inside one section: 914.2 mandates the electric standard, 914.4.1 regulates the timer on a "main burner."

A wood-fired kiuas falls through to the generic solid-fuel room heater machinery, which never says the word sauna. IRC M1410 sends it to UL 1482 and demands noncombustible floor protection 18 inches beyond the appliance on every side. UL 1482's own scope covers fire chamber assemblies intended for attachment to a residential-type chimney. A smoke sauna is defined by not having one.

One number out of the clearance sections is worth taping to a wall, because it is the rule this trade breaks most often. You cannot heat-shield your way below 12 inches. IRC M1306.2.1 and IMC 308.7 both bar the clearance reduction table from taking a listed solid-fuel appliance under 12 inches, whatever the shield is made of.

The masonry heater already won this exact argument

A masonry heater is a site-built, solid-fuel, heat-storing appliance. So is Lybäck's. One of them has a clean path through American code, and it is not the sauna.

IRC R1002.2 gives masonry heaters two compliance paths and lets the builder choose: comply with ASTM E1602, or be listed and labeled to UL 1482 or CEN 15250. The first path requires no listing, no label, no third-party certification. Same in the 2024 edition, and IBC Section 2112 carries the same structure, so this is not a residential-only favor.

Then read the standard the code points at. ASTM E1602-03(2026) says at scope 1.3 that it "applies to the design and construction of masonry heaters built on-site" and "does not apply to the construction/installation requirements for component systems that have been safety tested and listed." The site-built path is not a fallback for appliances that failed to get listed. It has a standard written exclusively for it, which throws listed products out.

Site-built work even earns a clearance concession on its own merits. R1002.5 sets 36 inches to combustibles, citing NFPA 211, then drops it to 4 inches where the heater wall is at least 8 inches of solid masonry and the heat exchange channels at least 5. A ninefold reduction bought with mass and geometry instead of a label.

The federal air rules line up the same way. Sauna stoves sit outside the residential wood heater standards by definition, because 40 CFR 60.531 defines a wood heater as an appliance intended for residential space heating, and EPA has said so twice in writing: for Harvia Oy, whose heaters are "intended to heat the sauna room only and not to be used for residential heating" (83 FR 22668, May 16, 2018), and for Lamppa Manufacturing of Tower, Minnesota, whose stoves are "intended solely for the purpose of heating a 'sauna hot-room'" (84 FR 9783, March 18, 2019). Masonry heaters are excluded too, and EPA's own guidance states that "masonry heaters currently do not require EPA certification."

The agency proposed regulating masonry heaters in 2014 and walked away, and its own fact sheet gives a reason that transfers directly to a sauna: it floated accepting a computer simulation instead of a performance test "because the heaters are built on-site, testing each individual heater could be difficult," and concluded "no further quality control would be required for these units, because each is unique."

One appliance got a code section, an ASTM guide, a clearance concession and a federal exclusion. The other got a federal exclusion and nothing else.

The correction to repeat when it comes up: the story that sauna stoves are EPA-exempt because they are used intermittently is wrong. Intermittent use appears nowhere in the agency's reasoning. The two determinations above are the documents to send.

Nobody has ever asked

The obvious next sentence is that a commercial smoke sauna is impossible to permit here. We went looking for the case that proves it and could not find one in either direction. No operating public savusauna in the United States, and no denial either. No permit record, no variance, no code-appeal decision.

The closest anyone got was Orcas Island, Washington. Ryan Brush ran a Kickstarter in autumn 2024 to build what local press called the first publicly accessible Finnish smoke sauna in America in over a century, working with Finnish builder Jarmo Hiltunen. The campaign record shows $15,081 raised against a $559,890 goal from 29 backers, cancelled by the creator on October 8. The project domain no longer resolves.

It died at fundraising and never reached a building department. The regulatory question was never asked, which is a more useful finding than a prohibition, because "nobody has applied" is a far easier problem to fix than "a regulator said no."

Worth knowing where it would have landed. Washington's public bathing rules expressly do not apply to steam baths and saunas, so the health department would not have been the gatekeeper at all. It would have come down to one building official reading the alternative means provision.

The chimneyless saunas that survive in North America are museum pieces. Hanka Homestead in Michigan, the 1868 Barberg-Selvälä-Salmonson sauna at Cokato, Minnesota, the 1924 savusauna at Embarrass, the relocated Korhonen farm sauna at Oulu, Wisconsin. Toured, not fired. The Kero farmstead in Carbon County, Montana holds the whole American pattern in one building: its National Register nomination records walls blackened from its years as a chimneyless sauna, and a later generation adding a stove and a chimney. It is still a working sauna. It stopped being a smoke sauna in order to stay one.

The supply side is empty to match. The North American Sauna Society states flatly that "smoke sauna kits are not commercially available in the US."

And the fire data points the other way

Every mechanism above treats solid fuel as the hazard and electricity as the safe default. Finland, which has more sauna fire data than anywhere on earth, does not find that.

Finnish public broadcaster YLE reported roughly 400 sauna fires a year, and that "noin kaksi kolmasosaa saunapaloista syttyy sähkösaunoissa": about two-thirds start in electric saunas. Pasi Paloluoma, fire chief and fire investigator at the Southwest Finland Rescue Department, put the leading cause down to carelessness, inattention or human error. That reporting is from November 2017, so take it as the best available rather than current. The recent counts come from the safety regulator Tukes: 98 sauna fires in the national database last year, 107 and 92 in the two before, with laundry drying in the sauna and objects left on the heater as the common causes.

Set that beside the American posture. A homeowners underwriter will ask whether the wood stove is UL listed, whether a permit was pulled, whether a licensed contractor installed it, whether it clears 36 inches. Nobody asks anything about the electric heater, which is where the Finnish data puts most of the fires, and where the leading cause is what the bather did rather than what the fuel is.

What to do about it

Specifying a wood-fired sauna for a commercial project: ask for the UL 1482 listing, the model it covers, and the name of the listing body, in that order. A European certification is not a US listing and your inspector will say so.

Ask about the model specifically, because the listing does not follow the price. Lamppa's own comparison table for the Kuuma line:

Model	UL 1482 listed by PFS	Price
Classic Kuuma Legacy (small)	Yes	$1,795
Kuuma Low Profile (small)	No	$2,795
Kuuma BluFlame (small)	No	$3,995

The cheapest stove in the range is the only listed one. Lamppa is also the manufacturer being straightest with buyers: listing status published per model, certification maintained through quarterly inspections with a serialized label on each stove, and a plain statement that the stoves are not EPA-certified residential wood heaters because that is not the applicable category. The listing body once called PFS-TECO now operates as NFPA Global Solutions, so an older certificate carries the old name.

We could not find a UL, ULC, ETL or CSA listing for any wood-burning sauna heater from Harvia or HUUM. Harvia's US storefront sells wood-burning models and the Pro 20 page we checked shows no North American mark, while Harvia's US electric heaters carry ETL. That is a scoped negative describing what we found on the manufacturers' own US pages, and it is the question to put to a rep in writing.

Building something genuinely unlisted: the door is the alternative materials provision, and you need the right section number because the 2024 codes renumbered it and the IRC did not land where the others did. It is IBC 104.11, IRC R104.11 and IMC 105.2 in the 2021 codes; IBC 104.2.3 and IMC 104.2.3 in the 2024 codes, but IRC R104.2.2.

The listing mandate is conditional by construction. IMC 301.7 requires appliances to be listed and labeled "unless otherwise approved," pointing straight at that provision, and IBC 1703.4.1 goes further: where the technical data is "satisfactory proof of performance for the use intended, the building official shall approve the use." The 2024 codes then make a stamped engineering analysis a first-class substitute for a listing, at IBC 104.2.3.6.2 and IRC R104.2.2.6.2, where a report "prepared by a qualified engineer, specialist, laboratory or specialty organization acceptable to the code official" carries the argument.

So: an engineer, a stamped package argued against the intent of the fire provisions, and a pre-application meeting in writing before the foundation goes in. Skip the field evaluation calls. That route is scoped to electrical equipment: IAS accredits field evaluation bodies against a criteria document titled for unlisted electrical equipment, OSHA's NRTL program certifies against electrical standards in a workplace regulation, and the one commercial fuel-burning field evaluation service publishes a standards list of boilers, industrial ovens and gas burners without a single solid-fuel standard on it.

Or somebody writes the section

That route works and it costs an engineer every time, per project, forever. Masonry heaters got out of it by getting a code section, and they got the section because an industry body did the work: the Masonry Heater Association says it developed ASTM E1602, funded the lab testing and built a performance database.

Sauna has the same appliance physics, the same site-built problem, and a finished template sitting in R1002. What it needs is an ASTM-style construction guide for site-built sauna stoves, prescriptive clearances earned by mass, and an IRC proposal pointing at the guide. Nobody has filed one.

There is even a deadline attached. The 2024 IRC still references E1602 at its 2003(2017) reapproval, and ASTM reapproved the guide as 03(2026) on January 26 this year. The 2027 IRC has to update that pointer anyway, which makes it the cycle to attach a sauna proposal to.

Meanwhile the company that made Lybäck's heater is going the other way. Tulikivi is entering the US on the electric track, running UL certification on its Kevo collection per its Q1 2026 interim report, which we covered in May. A 130-year-old soapstone business built on wood-fired mass is crossing the Atlantic with an electric product, because electric has a standard, a lab and a code section that names it.

The wood-fired tradition is not illegal in the United States. It is unwritten, which in commercial practice costs about the same, and stays that way until someone files the paperwork.

Original reporting on Christer Lybäck's sauna by Ulla Ora in Sauna-lehti 2/2026, the Finnish Sauna Society's quarterly, in its Minun saunani column. The issue is available in full at sauna.fi. We do not republish their photography.