Steam & Oak Hiili 2m Black Thermowood Barrel Sauna (Harvia 9kW, WiFi Option)

Steam & Oak Hiili 2m Black Thermowood Barrel Sauna

A black barrel sauna, finished at the factory rather than painted in a yard afterwards. Almost every black barrel sold in this country is somebody's paint job on a natural barrel. This one comes out of the line in Coal Black, on thermally modified timber, with the option of black or mirrored glass to match.

The 44mm walls, and why we keep going on about them

Most imported barrel saunas are built from 38mm or 40mm staves. We have priced up more than forty of them this year and that is where the bulk of the market sits. This one is 44mm.

On a barrel that matters more than it would on almost any other garden building, because the wall is the entire thermal envelope. There is no cavity, no insulation batt, no inner lining. The timber is the insulation, and it is also the heat store.

So the extra 6mm over a 38mm barrel does two jobs at once:

• It insulates better. Thermal resistance rises directly with thickness, so on the standard figure for softwood a 44mm wall gives you roughly 16% more resistance than a 38mm wall and about 10% more than a 40mm one.
• It stores more heat. That same 16% is 16% more timber mass sitting around you. Once a solid timber sauna is up to temperature it holds and re-radiates rather than needing constant topping up, which is what you notice on the second and third session of an evening rather than the first.

There is a third benefit that is harder to put a number on. Thicker staves are stiffer and cup less as they move through wet and dry seasons, so the joints between them stay tighter for longer. In a structure this small, air leaking through gaps costs you more heat than the wall itself does. That is the failure nobody photographs.

A solid back, and why we would leave it that way

This barrel ships with a solid rear wall as standard. No half moon window, no panoramic glass.

Plenty of barrels are sold with a glazed back and they do look wonderful in a photograph. What the photograph does not show you is that a glass panel loses heat somewhere in the order of ten times faster than the insulated wall it replaced. Put a large one in the back of a small barrel and you have quietly undone a good part of what the 44mm walls were doing for you, and you will pay for it on the electricity bill every session for as long as you own it.

There is also the practical bit. A rear window looks out at whatever is behind the sauna, which in most gardens is a fence, and at night it is a black mirror. The view you actually want is through the door, on your way in and out.

If you do want glazing we can do it. Two rear windows, a half panoramic or a full panoramic are all available, as are black and mirrored glass. Just ask, and we will tell you honestly what it costs you in heat before you commit.

Thermowood

Thermally modified timber is wood that has been baked at around 200°C in low oxygen with steam, rather than treated with preservative. The heat drives out the resin and breaks down the sugars that rot fungi feed on. What you get is timber that moves far less with the weather and resists rot for decades, using nothing but heat and steam. No chemicals, ever, and nothing to reapply.

It also takes a dark finish beautifully, which is the other reason this one is black.

Your heater, and whether you want it on your phone

• Harvia Cilindro PC90 9kW. The classic Cilindro pillar with the tall stone column and 90kg of stones. Controls built into the heater. £7,995.
• Harvia Cilindro PC90XW 9kW WiFi. The same heater with MyHarvia app control, so you can start it from the kitchen or on the way home. £8,695.

The WiFi version comes with the Harvia door sensor fitted. That is not an accessory, it is what the electrical sauna standard requires before any heater is allowed to start remotely, and it is not in the box with the heater. A good number of quotes leave it off and the customer finds out later.

Mood lighting, included

Both LED runs are fitted as standard: one under the benches and one behind the backrests, plus the Harvia light fitting. Lit from below and behind rather than from above, which is the difference between a sauna you want to sit in with the door shut and a shed with a bulb in it. Most sellers charge £300 to £500 for this and charge it twice if you want both runs.

Specifications

• Length: 200cm
• External diameter: 235cm
• Height: 240cm
• Weight: 800kg
• Seats: 4
• Wall thickness: 44mm thermowood
• Exterior finish: Coal Black
• Benches: Linden
• Floor: Terrace boards
• Roof: Two layer bitumen shingles
• Rear wall: Solid as standard, glazing available to order
• Use: Outdoor only

What's included

• Barrel shell in 44mm thermowood, factory finished in Coal Black
• Pre-cut wall staves and tension bands
• Linden benches
• Terrace board floor
• Two layer bitumen shingle roof
• Tempered glass door
• One Harvia light fitting inside, two Harvia lights outside
• LED lighting under the benches and behind the backrests
• Your chosen Harvia Cilindro 9kW heater
• Harvia door sensor, on the WiFi version

Available to order

A 50cm length extension, taking it to 2.5m. Rear or front glazing in tempered, black or mirrored glass. A Bluetooth speaker system. Stainless steel banding. Alternative bench woods and exterior finishes from a twelve colour range. Tell us what you want and we will price the configuration properly rather than guessing.

Before you order: your electricity supply

A 9kW heater is not a plug in appliance. 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.

Tell us your supply type and your main fuse rating and we will tell you what will and will not work before you commit to anything.

Delivery and site

• Weight: 800kg, palletised. You will need a way to move it from the kerb.
• Base: A stable, level base must be ready before delivery.
• Assembly: Self assembly, typically two people over one to two days.

Not sure this is the right size for you? Read our complete UK Sauna Buying Guide, or message us and we will confirm the specification with you before you order. If you want the same build at three metres, see the Vanne 3m Thermowood Barrel.