Gas Sauna Heater — Botnia 81, 8.1 kW Off-Grid Propane | FinSteam

Steam & Oak is the first UK retail partner for FinSteam — bringing this Finnish gas sauna engineering to British gardens, off-grid cabins, custom builds and existing-sauna retrofits.

The original FinSteam gas heater — drop into your existing sauna, or build around it

The Botnia 81 is the original FinSteam workhorse — 8.1 kW, certified, the heater that started the brand. Drop it into your existing barrel sauna, cube sauna, cabin, custom build, or off-grid setup; or buy it to specify a new sauna around. Connect a UK propane bottle outside via a 37 mbar regulator, light the heater, and you're in genuine 70-75°C Finnish sauna heat in 15 to 20 minutes. No electricity, no chimney, no flue. Turn the dial.

Upgrading your current sauna? Here's what fits where

The Botnia 81 is certified as a standalone gas appliance, which means it can be installed in any sauna structure provided you meet the FinSteam installation specifications (clearances, ventilation, base, gas connection). Common retrofit scenarios:

• Existing barrel sauna with no heater fitted (very common with imported Eastern European barrels) — the Botnia 81 R11S or R14S is the typical pick. The Njord heat shield in the S variants halves the clearance to combustible timber, which makes it fit barrels where a base-config heater wouldn't.
• Existing barrel / cabin with a tired wood-fired stove — replace it with a Botnia and you skip the chimney, the fire-tending, the 30-45 minute warm-up. Same sauna, a much better daily experience.
• Existing electric sauna with a dead element — replace the element + heater + the consumer-unit + the electrician callout with a Botnia. No more sauna-trips-the-fuses, no more circuit upgrades.
• Custom build / self-build — buy the Botnia 81 O (base, no cage) if you're sourcing your own Orbis cage, or any of the R configurations to ship matched and ready.
• Off-grid cabin / cottage / Airbnb — the Botnia is the easiest way to add real sauna heat where the mains can't reach.

Why a gas sauna heater (and why it beats wood-fired or electric)

For owners considering an upgrade, the headline comparison:

A clever piece of engineering — the certified safety case

Running gas safely inside a small, enclosed, oxygen-hungry space like a sauna is genuinely hard. FinSteam solved it with patented burner technology delivering clean, stable combustion, wrapped in two layers of automatic safety:

• Oxygen Depletion Sensor (ODS) — continuously monitors the oxygen level inside the sauna and automatically shuts off the gas if it drops to approximately 18% — well above any level dangerous to occupants. This is the same standard used in indoor gas appliances regulated by the EU.
• Flame monitoring — cuts the gas instantly if the flame is lost for any reason (e.g. accidental knock, sudden draft, gas supply interruption).

FinSteam's stated claim: this is the only CE-marked, electricity-free sauna gas heater on the European market. AENOR-tested under EU Gas Appliance Regulation 2016/426. Across the last 12 months, FinSteam record zero warranty returns on the heater.

Will it fit my sauna?

• Insulated saunas: 4 to 12 m³ internal volume — covers virtually every domestic barrel, cube, cabin and custom build.
• Non-insulated saunas / tents / lightweight builds: 4 to 8 m³ — the lower insulation means less working volume.
• Heating speed: 15 to 20 minutes from cold to 70-75°C in normal UK conditions.
• Stone capacity: up to 20 kg with Orbis 11 cage, 25+ kg with Orbis 14.
• Clearance to combustible timber: 500 mm sides, 1200 mm ceiling. The Njord heat shield halves the side clearance to 250 mm.

If you're not sure your sauna fits the spec, send us the internal dimensions and a photo by WhatsApp or email — we'll tell you straight, before you commit.

Key specifications

• Power: 8.1 kW.
• Gas: UK propane (I3P, 37 mbar) — also factory-configured for butane/propane mix (I3P/B, 30 mbar) on request.
• Gas consumption: 0.6 kg/h at full output. A UK 13 kg propane bottle runs the heater at full output for around 20 hours; throttled at temperature, much longer.
• Dimensions: 61 × 51 × 30 cm.
• Weight: ~9.8 kg (configuration-dependent).
• Heat-up time: 15-20 minutes to 70-75°C.
• Sauna size range: 4-12 m³ insulated · 4-8 m³ non-insulated.
• Safety: EU Type-Examination Certificate (AENOR, Gas Appliance Regulation 2016/426). ODS auto-shutoff. Flame monitoring.

Which configuration should I pick? — every variant explained

The Botnia 81 ships in 5 configurations. The heater chassis is identical in every one — what changes is the cage and the safety pack:

Botnia 81 O — heater only, no cage (the bare base)

The heater on its own, no Orbis cage included. Pick the O only if you already own a compatible Orbis cage from a previous FinSteam, or you're building a fully custom sauna and you want to specify the cage separately. For everyone else, the R11 is the cheapest sensible entry point — you need a cage to load stones, and Orbis is the cage FinSteam designed for this heater.

This is the cheapest variant in the range and the most rarely picked — most retrofit buyers want at least the R11.

Botnia 81 R11 — heater + Orbis 11 stone cage

The default configuration for most domestic retrofits. The Orbis 11 cage takes 20-25 kg of sauna stones, which is the right thermal density for a 4-8 m³ sauna (most barrels, smaller cubes, smaller cabins). Pick R11 if you're retrofitting a domestic barrel (typical 3-5 m³ internal volume) or a small-to-medium cabin sauna, you don't need the safety pack, and you want the cheapest fully-functional configuration.

Botnia 81 R14 — heater + Orbis 14 stone cage

The Orbis 14 holds 25 kg+ — more stones, more thermal mass, stronger löyly response when you ladle. Pick R14 if your sauna is on the larger side (8-12 m³ — bigger cabins, larger custom builds), or you specifically want a more powerful steam response from the stones. For a typical UK domestic barrel, the R11 is enough and the R14 is overkill.

Botnia 81 R11S — R11 + Njord heat shield + Halo safety rail (the safety pack)

The "S" configuration adds two standard items to the heater:

• Njord heat shield — a non-combustible steel shield between the heater and the timber walls of your sauna. Halves the required clearance to combustible timber (500 mm sides → 250 mm). For most barrel saunas this is the difference between the heater fitting and not fitting.
• Halo safety rail — a wood-clad circular rail around the top of the heater. Prevents accidental contact with the hot stone cage during a session.

Pick R11S if: you're retrofitting a tight barrel sauna where 500 mm side clearance won't fit, you have kids using the sauna, you're running any commercial / hire / holiday-let use, or you want a Gas Safe engineer or insurance broker to look at the install and see the full safety story. Standalone, the Njord retails at ~£189 and the Halo at ~£249 — buying both separately + the R11 base costs more than upgrading to the R11S in the package.

Botnia 81 R14S — R14 + Njord + Halo (the full safety pack with larger cage)

Same safety pack as R11S, but with the larger Orbis 14 cage. The flagship Botnia configuration. What every commercial / hire operator should choose — bigger thermal mass for repeat sessions, full safety pack for insurance compliance. Also recommended for any household-with-kids retrofit into a larger cabin or barrel.

Not sure? R11S is the sensible default for most domestic retrofits into existing barrel saunas. R14S is the default for commercial / hire use and larger builds.

The components, explained individually

Orbis 11 / Orbis 14 stone cage (included in R11/R14/R11S/R14S)

The Orbis is the FinSteam-designed stone cage that sits on top of the heater chassis. Fully compatible across all FinSteam heaters — including older Botnias bought before the Orbis line existed. Stone capacity 20-25 kg (11) or 25 kg+ (14). The cage is what holds the sauna stones in position above the burner — stones aren't just decoration, they're the thermal mass that gives you löyly when you ladle water on them. Most other stone cages aren't sized for this heater.

Njord heat shield (included in R11S/R14S, sold standalone)

A non-combustible steel shield, designed by FinSteam, that sits between the heater and any timber surface. The shield reduces the radiated heat reaching the timber by enough that the required clearance to combustible timber drops from 500 mm to 250 mm on the sides. In practical terms: most UK domestic barrel saunas (and smaller cube saunas) don't have 500 mm of clear space around the heater position. The Njord makes them fit. If you're retrofitting an existing sauna, the Njord is usually the deciding factor on whether the install works at all.

Halo safety rail (included in R11S/R14S, sold standalone)

A circular wood-clad rail that fits around the top of the heater, preventing accidental contact with the hot stone cage during a session. Important in three scenarios: family use with children, commercial / hire / holiday-let use (insurers expect to see it), and tighter sauna interiors where bench positions are close to the heater.

The full retrofit picture — what you'll need on top of the heater

If you're retrofitting an existing sauna, the heater is the centrepiece but not the whole story. Plan for:

• UK propane regulator + hose kit (I3P 37 mbar, 27 mm clip-on for Calor bottles). FinSteam don't supply this — it's our UK gas kit. Sold standalone, included in every NOIR package.
• 40 kg sauna stones sized for the Orbis cage. Sold standalone.
• Non-combustible base for the heater — ≥30 mm thick, ≥300 × 300 mm (concrete slab or stone tile) directly beneath. Sourced locally.
• Natural ventilation provision in your sauna structure: air intake ≥350 cm² low next to the heater, air exhaust ≥250 cm² high in the opposite corner. Both must draw fresh air from outside and discharge directly to outside — wooden louvre vents only, not plastic disc/twist valves. If your existing sauna doesn't have this, you'll need to retrofit the vents before the heater can be used.
• Standard UK 13 kg Calor propane bottle (or larger for commercial use) — bought locally from BBQ / camping / petrol-station retailers.
• If you're doing a fixed install (heater anchored into the sauna): a Gas Safe registered engineer to make the gas connection. UK law.

Portable by default. Gas Safe registered if you fix it down.

The heater ships as a portable LPG appliance. You connect a UK propane bottle outside via a UK-spec 37 mbar regulator and CE-marked hose — set up like a patio heater or BBQ. Used this way, you do not need a Gas Safe registered engineer. If you choose to permanently fix, bolt down, or build the heater into a fixed sauna structure (most retrofit installs do this), UK regulations require the gas connection to be made by a Gas Safe registered engineer. Either path is supported by FinSteam's installation specifications.

Install requirements (mandatory)

The Botnia 81 ships with FinSteam's installation manual. The headline requirements you should design around BEFORE buying:

• Natural ventilation only. No mechanical / fan ventilation — gas heaters must NOT be used in mechanically ventilated saunas. Air intake ≥350 cm² low next to the heater (examples: 200×175 mm or 250×140 mm rectangular, or Ø210 mm circular). Air exhaust ≥250 cm² high in the opposite corner. Wooden louvre vents only — NOT round plastic disc / twist valves.
• Clearance to combustible timber: 500 mm sides, 1200 mm ceiling. The Njord heat shield (R11S / R14S) halves the side distance to 250 mm. A fire-protection stone board on panelled walls quarters it.
• Non-combustible base: ≥30 mm thick, ≥300 × 300 mm beneath the heater.
• Gas connection: CE-marked hose with internal Ø ≥ 9 mm, fixed at both ends, kink-free. UK 37 mbar propane regulator. Propane bottle outside, upright, stable.

Full installation PDF on request. Send us your retrofit plan before you commit — we'll review it with you, free, and tell you what to change.

Made in Finland. Backed by a track record.

Manufactured in Finland by FinSteam Ab Oy, with all heater components sourced from Europe — not a re-badge of an Asian import. Spare parts ship direct from the FinSteam factory. EU Type-Examination Certificate (AENOR-tested under Gas Appliance Regulation 2016/426). As the official first UK retail partner, Steam & Oak holds UK stock, handles UK service and warranty work, and gives you a real phone number when something needs attention. Zero warranty returns on the heater across the last 12 months.

Complete the install

• UK propane regulator + CE-marked hose kit (I3P 37 mbar, 27 mm clip-on for Calor 13 kg bottles) — the missing piece between the heater and your first burn. Not supplied with the heater.
• 40 kg sauna stones — pre-washed, sized for the Orbis cage.
• Orbis 11 or Orbis 14 stone cage — if you bought the Botnia 81 O base, or you're upgrading an older Botnia.
• Njord heat shield + Halo safety rail — if you didn't pick an S variant.
• FinSteam Fritid tent — if you're building a portable setup around the heater rather than retrofitting an existing structure.

Delivery + documents

Free UK delivery on the heater. Stock status and lead time shown above the buy button.

Documents available on request: EU Type-Examination Certificate (AENOR) · EU Declaration of Conformity · Installation & safety manual · Ventilation specification · UK gas connection guide.

FAQs — retrofit-focused

I have an existing wood-fired barrel sauna. Can I convert it to gas with the Botnia?
Yes — and it's one of the most common retrofit scenarios we see. Remove the wood stove and its flue, seal the flue penetration in the roof, fit the Botnia 81 on a non-combustible base in the same position (the sauna will already have approximately the right airflow because it was designed around the wood stove). You'll need to fit FinSteam-spec natural ventilation if the existing vents are mechanical / closable plastic disc types. Most barrel sauna conversions need the R11S configuration (Njord heat shield to halve the clearance to the curved timber walls). Send us a photo of your barrel before you order — we'll tell you what you need.

My electric sauna heater has died. Can I swap it for the Botnia?
Yes — and you save the £1-2k electrician cost for replacing the electrical install. Remove the old electric heater and its wiring (electrically isolate properly). Fit the Botnia on a non-combustible base — most electric saunas already have the right base. You'll need to add a wall gland for the gas hose, and provide natural ventilation if the existing was mechanical. The cabin's existing insulation works fine for gas — you're just changing the heat source. Worth checking the cabin volume sits within the Botnia's 4-12 m³ insulated spec before you commit.

Will it fit my cube / cabin sauna with limited clearance?
Probably yes with the R11S or R14S — the Njord heat shield drops the required side clearance from 500 mm to 250 mm. Most UK cube saunas (4-8 m³) work with the Njord; some very tight installs need a fire-protection stone board on the wall to quarter the clearance to 125 mm.

Do I need a Gas Safe engineer to install this in my existing sauna?
Depends on the install. If you use it portably (heater stands on the base, propane bottle outside, gas hose runs through a wall gland) — no, you don't. If you permanently fix the heater into the sauna structure (anchored, gas line routed and fixed) — yes, UK regulations require a Gas Safe registered engineer for the gas connection. Most retrofit installs go the fixed route because it's neater.

What about ventilation in my existing barrel — what do I need to check?
FinSteam require natural (gravity) ventilation only. Air intake ≥350 cm² low next to the heater, taken from outside. Air exhaust ≥250 cm² high in the opposite corner, discharged directly to outside. Wooden louvre vents — NOT plastic disc valves (FinSteam specifically exclude these). If your existing sauna has plastic disc vents, you'll need to swap them. If it has mechanical / fan ventilation, you need to remove it — gas heaters cannot be used with mechanical ventilation.

How does the Botnia compare to the Aurora 81?
Same 8.1 kW chassis, same patented burner, same certifications, same safety case, same heat-up time, same löyly response, same heating performance. The Aurora is FinSteam's newer premium line — more modern design language, intended for builds where the heater is part of the aesthetic. The Botnia is the original — slightly lower price, identical performance. If function-per-pound matters most, the Botnia is the smarter buy. If you want the newest FinSteam product, look at the Aurora 81.

What stones go in the cage — can I use barbecue lava rocks?
No — sauna stones are specifically sized and selected for thermal cycling. Lava rocks crack and shatter under repeated heating. Use proper FinSteam sauna stones, sized for the Orbis cage. They last 2-3 years of heavy use; 40 kg is enough to fill the cage with proper thermal density.