Steam & Oak Holvi 350 Thermowood Barrel Sauna (Gas, Electric or Wood-Fired)

Steam & Oak Holvi 350 Thermowood Barrel Sauna

The Holvi 350 is a 3.5 metre barrel laid out in three spaces: a 60cm covered terrace at the door, a 1 metre changing room with its own benches, and a hot room about 1.9 metres long behind a tempered, tinted glass door. The changing room is what makes a barrel this size work through a British winter. You undress and cool down in a dry, sheltered room, the hot room stays hot because its door opens into the changing room rather than outdoors, and wet towels stay out of the heat. It comes in two widths, Ø1.97m or the taller Ø2.27m, both in 46mm thermowood staves with stainless steel bands.

Every part of the layout can be changed. The barrel can be built without the changing room for a longer hot room, or without the terrace, and we will confirm the hot room size for any layout before you order.

Which width?

• Ø1.97m. 2.08 metres high, a 4.61m³ hot room. Quicker to heat and a smaller heater does the job. Door 70 x 160cm.
• Ø2.27m. 2.38 metres high, a 6.19m³ hot room. More headroom on the upper bench, which is where the heat is, and a little more room to lie down. Door 70 x 180cm.

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, and 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 and resists rot without chemical treatment, in a structure that depends on staying tight.

Choose your heater at checkout

• Shell only. The complete sauna, you source your own heater.
• Harvia Cilindro PC70 6.8kW. The Cilindro pillar heater with its tall column of stones and controls built into the heater. Harvia rate it for rooms of 6 to 10m³.
• Harvia Cilindro PC70XW 6.8kW 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.
• Harvia Cilindro PC90 9kW. The classic Cilindro pillar with its tall stone column, 90kg of stones, controls built into the heater. Harvia rate it for rooms of 8 to 14m³.
• 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 M3 wood fired. The classic Finnish log burning stove, rated by Harvia for rooms of 6 to 13m³. No electrics at all, no standing charge, and the ritual of building the fire. Supplied with a stainless steel chimney, and we confirm the chimney route with you before you order.
• Harvia M3 SL wood fired, through wall feed. The same stove, loaded through the wall from outside the hot room, so you feed the fire without letting the heat out or carrying logs past bathers.

Sizing the heater. Harvia size heaters on the room volume, then add 50% for solid log walls and about 1.2m³ for every square metre of glass, because both soak up heat that an insulated panel would not. On the Ø1.97m Holvi 350 the hot room behaves like about 8m³, and on the Ø2.27m like about 10m³. So the narrower barrel gets the 6.8kW Cilindro and the wider one the 9kW. The heater list at checkout only shows the heaters that suit the width you pick.

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

Also available with gas

Pick a gas option at checkout and the sauna ships gas ready: ventilation built for gas, plus a FinSteam gas heater package that runs on a standard UK propane bottle. No electrician, no chimney and no fire to tend. It heats in around 15 minutes from a dial.

• Botnia 81. Our standard 8.1kW gas heater. Everything you need to run the sauna.
• Aurora 81. The premium version of the same 8.1kW heater, with a better finish and detailing, oxygen depletion auto shut off and flame monitoring.
• With the safety pack. Adds the Njord heat shield and the Halo guard rail. The heat shield lets the heater sit closer to the timber wall, and the rail stops anyone brushing the hot stones. If you have children, guests, or you rent the sauna out, choose this one.
• Without the safety pack. Heater and stone cage only. Talk to us first, because in a curved barrel the wall leans in above the heater and we will usually recommend the heat shield.

FinSteam rate the 8.1kW heaters for barrels and other uninsulated rooms of up to about 8m³ of air, which is why gas is offered only where the hot room fits that range.

Every gas option includes the heater, the Orbis stone cage, 40kg of pre washed sauna stones, a UK propane regulator and CE marked gas hose, and our fitting and commissioning. The gas variants are built with wooden louvre vents at the sizes FinSteam specify: a low intake beside the heater drawing air from outside, and a high exhaust in the opposite corner. You source a standard 13kg propane bottle locally, and a fixed gas connection needs a Gas Safe registered engineer. See the full gas heater range.

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. The 6.8kW heater has its own supply requirement and we confirm that with you directly rather than printing a figure here. Budget for a qualified electrician and a Part P sign off. The wood fired options and the FinSteam gas variants need no electrical supply for the heater.

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
• Terrace: 60cm covered terrace at the door end
• Changing room: 100cm, with two pine side benches and a tempered tinted glass door into the hot room
• 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

What's included

• Barrel in 46mm thermowood
• Stainless steel tension bands
• Two benches in the hot room
• Covered 60cm terrace
• Changing room with two pine benches and a tinted glass door to the hot room
• Glazed timber front door with handle and lock
• Two double glazed windows
• Timber floor
• Bitumen shingle roof
• Heat resistant heater protection plates
• Your chosen heater, on all variants except shell only, with the chimney on the wood fired options
• Harvia door sensor, on the WiFi versions
• Gas ventilation set, Orbis stone cage, 40kg stones, propane regulator and gas hose, on the gas variants

Options available

The Holvi 350 can be configured to suit your garden:

• Width: Ø1.97m or Ø2.27m, selected at checkout
• Layout: without the changing room, or without the terrace
• Windows: at the front, at the back, or both
• Panoramic glass: tinted, toughened glass across half of the back wall, or the entire back wall with a heater safety fence
• Glass front: a full tinted glass facade with a glass entrance door
• Door: a tinted glass door, or a wood framed glass door with lock, in place of the timber door
• Benches: premium benches with back rests, in the hot room and the changing room
• Roof: bitumen shingles in black, grey, red or green, or natural wooden shingles
• Lighting: LED strips under the benches and behind the back rests, in white or colour, and a sauna lamp with cover
• Comfort: head rests and back rests
• Safety: a timber heater safety fence
• Finish: factory painting in a choice of colours
• Accessories: bucket and ladle, thermometer and hygrometer, sauna hourglass, water tank for the wood stove

Ask us for a configured quote.

Specifications

• Length: 350cm
• Width and height: Ø197cm and 208cm high, or Ø227cm and 238cm high
• Hot room: 4.61m³ (Ø1.97m) or 6.19m³ (Ø2.27m)
• Changing room: 100cm
• Terrace: 60cm
• Seats: 6 to 8
• Wall thickness: 46mm thermowood
• Floor: 18mm
• Door: 70 x 160cm (Ø1.97m) or 70 x 180cm (Ø2.27m)
• Windows: 2, each 29.5 x 58cm
• Weight: about 1,400kg (Ø1.97m) or 1,600kg (Ø2.27m)
• Use: Outdoor only

Delivery and site preparation

• Delivery: Flat packed on one pallet, 360 x 120 x 120cm, around 1,400kg (Ø1.97m) or 1,600kg (Ø2.27m). You will need a way to move it from the kerb. Factory assembled delivery is also available, quoted separately, and needs a crane on the day.
• Lead time: confirmed at order
• Base: a stable, level base must be ready before delivery. Send us photos of your site and we will tell you what it needs.
• Electrical: for the electric heaters, see the supply note above. Qualified electrician required.
• Gas: standard UK 13kg propane bottle, sourced locally. Gas Safe registered engineer required for a fixed connection.
• Chimney: the wood fired options need a flue, with clearance from buildings and overhanging trees.
• Assembly: self assembly from the kit, typically two people over one to two days

Want a longer hot room? The Holvi 400 keeps the same changing room and adds 50cm to the hot room. 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.