Steam & Oak Ruutu 230 Thermowood Cube Sauna with Glass Front (Gas, Electric or Wood-Fired)

Steam & Oak Ruutu 230 Thermowood Cube Sauna

Ruutu is Finnish for a square pane, the kind you look through. The Ruutu range is built around that idea: a squared cabin with softly rounded corners and a front that is almost entirely glass. The Ruutu 230 is 2.3 metres by 2.3 metres, in 46mm thermowood, held together with stainless steel bands, with a hot room of about 8.5m³ and a two metre bench run along the side wall.

Why the corners are rounded

On a conventional cube the roof and the walls meet at hard edges, and every edge is a joint where rain can sit and work its way in. On the Ruutu the roof curves down into the sides, so one continuous skin of bitumen shingles runs from the base on one side, over the top, to the base on the other. There is no roof to wall joint for water to find, and nothing flat for it to pond on. Inside, the same curve leaves fewer tight corners where air stalls.

The glass front

The front is 8mm tempered, tinted glass: two full height panes, one of them the door, and a narrow pane either side. That is roughly 3.1m² of glass looking out from the bench. Tinted glass cuts glare and gives some privacy from outside while the view from inside stays clear. Glass also loses heat far faster than solid timber, which is why the heater choice below matters more on this cabin than on a closed cube.

Why the bands are stainless

The Ruutu is built like a barrel: solid staves held in compression by steel bands, rather than thin cladding over a frame. Timber shrinks each time the sauna is heated and dries out, then swells again through a wet British winter, so the bands work constantly and need checking and re-tightening over the life of the sauna. Ordinary steel bands eventually rust, and rust runs down the timber and stains it. Stainless steel does not.

What thermowood actually does

Thermowood is timber that has been heat treated at around 200°C rather than chemically preserved. The process breaks down the sugars and resins that fungus feeds on and permanently reduces how much moisture the wood can reabsorb. The practical result outdoors is timber that moves less through wet British winters, resists rot without chemical treatment, and holds its shape in a structure that depends on staying tight.

A note on wall thickness: 46mm solid staves give the cabin plenty of thermal mass, but how warm a sauna stays is governed far more by the glass, the ventilation and the heater than by a few millimetres of timber. Choose the Ruutu for the design, the glass and the build rather than for a thickness figure.

Also available with gas — no electrician, no chimney, no fire to tend

Pick a gas option at checkout and your cabin ships gas-ready: engineered ventilation built for gas, plus a bundled FinSteam gas heater package — ready to light on a UK propane bottle the day it lands. Steam & Oak is the only UK retailer offering this on a thermowood cube. Hot in 15 minutes, turn a dial.

The Aurora 81 is the only CE-marked electricity-free sauna gas heater on the European market (FinSteam's stated claim), and the heater that powers the FinSteam NOIR Signature packages.

Why gas changes the equation

The real cost to your first löyly

An electric sauna's shelf price is not the price to your first session. The 9kW Harvia needs its own dedicated circuit on 10mm² cable, wired by a qualified electrician and signed off under Part P — typically £800–£1,500, more again over a buried run to the end of a garden, plus the wait to get one booked. The gas heater connects to a propane bottle outside: no dedicated circuit, no trench across the lawn, and it is hot on the day it arrives.

Against the wood fired M3, gas gives you the same freedom from the grid without the flue, the chimney route we would otherwise have to agree, or anyone building and tending a fire before every session.

What gas-ready means

The gas variants ship with wooden louvre vents at the FinSteam-specified sizes built into the cabin: intake ≥350 cm² low next to the heater drawing fresh air directly from outside, exhaust ≥250 cm² high in the opposite corner discharged directly to outside. FinSteam explicitly exclude plastic disc and twist valves. The vent configuration and the heater are certified together under EU Gas Appliance Regulation 2016/426. Pick a wood fired or electric variant and the cabin ships with the appropriate vent set for that heat type.

Which gas option?

And then: safety pack, or without?

Every gas option includes the heater, the Orbis stone cage, 40 kg of pre-washed FinSteam sauna stones, a UK propane regulator and CE-marked gas hose, and our fitting and commissioning. You source a standard UK 13 kg Calor propane bottle locally; a fixed gas connection needs a Gas Safe registered engineer. See the full gas heater range →

Or choose wood fired or electric

• Shell only. The complete cabin, you source your own heater.
• Harvia M3 wood fired. The classic Finnish log burning stove. No electrics at all, no standing charge, and the ritual of building the fire. Needs a flue, and we confirm the chimney route with you before you order.
• Harvia M3 SL wood fired, through wall feed. The same stove, loaded from outside the sauna room through the wall, so you feed the fire without letting the heat out or carrying logs past bathers.
• Harvia Cilindro PC90 9kW. The classic Cilindro pillar with its tall stone column, 90kg of stones, controls built into the heater.
• Harvia Cilindro PC90XW 9kW WiFi. The same heater with MyHarvia app control, so you can start it from the house. Supplied with the Harvia door sensor, which the electrical sauna standard requires before any heater can be started remotely. Most sellers leave that part off the quote.
• Harvia Legend PO110XW 10.8kW WiFi. This is the electric heater we recommend. App control as above, with more output. Harvia size heaters on the room volume, then add to that figure for solid timber walls and for every square metre of glass, because both soak up heat that an insulated panel would not. Run the numbers on the Ruutu 230 and its 8.5m³ hot room, with 3.1m² of glass across the front, behaves more like a 16m³ room. That is a lot to ask of 9kW on a cold day. It is £500 more than the 9kW WiFi.

We would rather sell you the right heater than the cheapest one. Tell us where the sauna is going and how you plan to use it, and we will confirm the output with you before you order.

Before you order: your electricity supply

The electric heaters are not plug in appliances. For the 9kW Harvia specify a 3 x 16A supply on three phase, or a single 50A supply on 10mm² cable if your property is single phase, which most UK homes are. Over a buried run to a garden building that cable size usually needs to go up again for voltage drop. Budget for a qualified electrician and a Part P sign off. The 10.8kW has its own supply requirement and we confirm that with you directly rather than printing a figure here. The wood fired M3 options and the FinSteam gas variants need no electrical supply at all.

Tell us your supply type and main fuse rating when you enquire and we will tell you honestly what will and will not work before you commit.

Build and finish

• Walls: 46mm thermowood staves
• Bands: Stainless steel tension bands
• Front: 8mm tempered, tinted glass: two full height panes including the door, plus two side panes
• Door: Tempered, tinted glass with a wooden handle
• Benches: Straight bench run along one wall as standard, in aspen or black alder. L shaped benches available as an extra
• Floor: 18mm timber floor boards
• Roof and sides: Bitumen shingles
• Trim: Decorative boards front and back
• Heater: Choose a FinSteam Botnia 81 or Aurora 81 gas package, a Harvia M3 wood fired stove, or a Harvia electric heater, at checkout — or shell only if you have your own

What's included

• Cabin in 46mm thermowood
• Stainless steel tension bands
• Glass front with glass door
• Straight sauna bench
• Timber floor
• Bitumen shingle roof and sides
• Heat resistant heater protection plates
• Ventilation set matched to the heater you choose, gas, wood fired or electric
• Your chosen heater, on all variants except shell only
• Harvia door sensor, on the two WiFi versions
• Orbis stone cage, 40 kg stones, propane regulator and gas hose, on the gas variants

Options available

The Ruutu can be configured to suit your garden. Available on the Ruutu 230:

• Heating: FinSteam gas, Harvia wood fired or Harvia electric, selected at checkout
• Benches: L shaped benches, wrapping round two walls for more seating
• Panoramic back: tinted glass across half of the back wall, so the view goes both ways
• Door lock: a lock for the glass door
• Roof: bitumen shingles in black, red, green or grey
• Lighting: LED strips under the benches and behind the back rests, in warm white or colour, and a sauna lamp with an alder cover
• Comfort: head rests and back rests
• Safety: a timber heater safety fence
• Accessories: bucket and ladle, thermometer and hygrometer, sauna hourglass, clothes hanger

Ask us for a configured quote.

Specifications

• External size: 240cm wide x 232cm deep x 226cm high
• Inside: about 223cm wide x 200cm deep, 194cm to the ceiling
• Hot room volume: about 8.5m³
• Seats: 4 comfortably, up to 6
• Wall thickness: 46mm thermowood
• Door: 65 x 177cm tempered glass
• Glazing: 8mm tempered, tinted, about 3.1m² across the front
• Use: Outdoor only
• Heater: FinSteam gas, Harvia wood fired or Harvia electric, selected at checkout, or shell only

Base, delivery and site preparation

• Footprint: 240 x 232cm. We recommend a base of about 260 x 250cm, so nothing overhangs and rain drips clear of the timber.
• Level: within about 5mm across the base. A cabin with a full height glass door is unforgiving, and a twisted base stops the door closing squarely.
• Base type: a reinforced concrete slab, paving slabs on a compacted sub base, or ground screws are all suitable. Send us photos of your site and we will tell you what it needs.
• Delivery: palletised specialist freight. Check your access route to the garden before ordering.
• Electrical (Harvia electric variants): dedicated circuit, a qualified electrician and a Part P sign off.
• Gas (FinSteam variants): standard UK 13 kg Calor propane bottle, sourced locally. Gas Safe registered engineer required for a fixed gas connection.
• Chimney (wood fired variants): the M3 options need a flue, with clearance from buildings and overhanging trees.

Want a porch or a barrel shape? See the Holvi 300 Thermowood Barrel. Not sure which configuration suits your garden? Read our complete UK Sauna Buying Guide, or message us and we will confirm the specification with you before you order.