Steam & Oak Holvi 300 Thermowood Barrel Sauna (Gas, Electric or Wood-Fired)

Steam & Oak Holvi 300 Thermowood Barrel Sauna

Holvi is Finnish for vault, and a barrel sauna is exactly that: a barrel vault turned into a room. The curved staves lock against each other and the steel bands hold them in compression, so the shell carries its own load round the curve without a frame. The Holvi 300 is the three metre model in the range: 46mm thermowood staves, stainless steel bands as standard, two double glazed windows, and the choice of a covered porch at the door end or a longer hot room without one.

With or without the porch

The same 3 metre barrel can be built two ways, and the choice changes how you use it.

• With the porch. The first 60cm of the barrel becomes an open porch under the same roof, with a bench either side. That is where you cool down between rounds and keep towels and footwear dry, and it means the sauna door opens onto a sheltered space rather than straight into the weather. The hot room behind it is about 2.2 metres long inside, 8.24m³ of air.
• Without the porch. The door sits in the end wall and the hot room runs almost the full length of the barrel, about 2.7 metres inside and roughly 10m³. More bench length, more room to lie down, and a larger space to heat.

Why the bands are stainless

A barrel only stays round and tight because the bands keep the staves pressed together. 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. On most barrels stainless banding is an upgrade you pay extra for. On the Holvi it is standard.

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 perfectly round.

A note on wall thickness: 46mm solid staves give the barrel 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. We would rather you chose the Holvi for the layout, the bands and the build 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 barrel 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 barrel. 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 barrel: 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 barrel 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 barrel, 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 barrel 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 glass, because both soak up heat that an insulated panel would not. Run the numbers on the Holvi 300 and the 8.24m³ porch version behaves more like 12 to 13m³, and the 10m³ version without a porch more like 15 to 16m³. On an exposed site or in February, we would rather you had the headroom than not. It is £500 more than the 9kW WiFi.

We would rather sell you the right heater than the cheapest one. Tell us where the barrel is going, which layout you want 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
• Benches: Two full length side benches in aspen or black alder
• Porch: 60cm covered porch with bench seating, or no porch
• Door: Multi layer glued timber door with a tempered double glazed window, wooden handle and lock
• Windows: Two tempered, double glazed windows, at the front or the back of the barrel
• Floor: 18mm timber floor boards
• Roof: Finnish bitumen shingles
• 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

• Barrel shell in 46mm thermowood
• Stainless steel tension bands
• Two side benches in the hot room
• Covered porch with bench seating, if you choose the porch layout
• Timber floor
• Bitumen shingle roof
• Glazed timber door with handle and lock
• Two double glazed windows
• 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 Holvi can be configured to suit your garden. Available on the Holvi 300:

• Heating: FinSteam gas, Harvia wood fired or Harvia electric, selected at checkout
• Layout: with the 60cm covered porch, or without
• Windows: positioned at the front or the back of the barrel
• Panoramic glass: tinted, toughened 10mm glass across half of the back wall, or the entire back wall (supplied with a heater safety fence)
• Glass front: a full tinted glass facade with glass door, best paired with the porch
• Glass door: a tinted glass door in place of the timber door, with an optional lock
• Roof: bitumen shingles in black, red, green or grey, or natural aspen wooden shingles
• 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, back rests, and back rests and armrests for the porch benches
• Safety: a timber heater safety fence
• Accessories: bucket and ladle, thermometer and hygrometer, sauna hourglass, clothes hanger

Ask us for a configured quote.

Specifications

• Length: 300cm
• External diameter: 227cm
• Height: 238cm
• Hot room: 220cm long and 8.24m³ with the porch, 270cm long and about 10m³ without
• Seats: 4 to 6
• Wall thickness: 46mm thermowood
• Bench depth: 60cm
• Door: 70 x 180cm
• Windows: 2, each 29.5 x 58cm
• Weight assembled: 950kg
• Use: Outdoor only
• Heater: FinSteam gas, Harvia wood fired or Harvia electric, selected at checkout, or shell only

Delivery and site preparation

• Delivery: One pallet, 310 x 120 x 120cm, around 1,400kg. You will need a way to move it from the kerb.
• Base: A stable, level base must be ready before delivery.
• Electrical (Harvia electric variants): See the supply note above. Qualified electrician required.
• 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.
• Assembly: Self assembly, typically two people over one to two days.

Want more width? The Vanne 3m Thermowood Barrel is 235cm across with a glass door. 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.