Modular Saunas
Celsium Herkus L.Architectural modular. Zero compromise.
A premium modular cube sauna in charred timber with panoramic glass, the design-led flagship of our modular range.
Overview
Celsium Herkus L Modular Sauna.
The Celsium Herkus L is our design-led modular flagship, a properly-insulated cube sauna in Shou Sugi Ban charred timber, with a full-height panoramic glass end wall and a Harvia heater that reaches temperature in 30 minutes.
Unlike a barrel, a modular cube is a fully-insulated timber-frame structure, 100mm rockwool between studs, vapour barrier, and knot-free western hemlock interior lining. It costs more to build, but it holds temperature, sits square into architectural garden schemes, and gives you a full-height interior rather than a curved ceiling.
This is the sauna to specify when the garden is a design piece rather than a lawn, sitting alongside a garden room, next to a hot tub deck, or as a standalone architectural feature in a contemporary courtyard.
Key features
What makes it different.
Fully-insulated cube construction
100mm rockwool insulation between timber studs, vapour barrier, interior hemlock lining. Holds temperature 30% better than an uninsulated barrel.
Shou Sugi Ban ebony exterior
Charred and oiled spruce cladding, architectural black that ages to graphite.
Panoramic glass wall
Full-height toughened glass end wall with matching glass door.
Harvia electric heater
9kW Finnish-made heater with rock cradle and digital control panel.
Full-height interior
Genuine 2.1m ceiling height, you can stand comfortably (barrels can't offer this).
Bespoke sizes available
This is the L; also available as M and XL. Interior layouts can be tailored to your space.
Specification
The numbers behind the object.
- Capacity
- 5–6 adults
- External footprint
- 3.0 x 2.4 m
- Interior ceiling height
- 2.1 m
- Cladding (exterior)
- Shou Sugi Ban charred spruce
- Insulation
- 100mm rockwool
- Lining (interior)
- Knot-free western hemlock
- Heater
- Harvia electric 9kW
- Heat-up time
- ≈ 30 minutes
- Power requirement
- 3-phase 400V or 32A single-phase
- Roof
- EPDM flat, hidden gutter
- Warranty
- 10 yr structural
Living with it
How it actually works day to day.
Insulation is the single biggest reason to spend more on a modular over a barrel. The Herkus L holds soaking temperature with the heater at low duty-cycle, meaning the running cost across a Scottish winter is materially lower than an uninsulated wood barrel of the same capacity.
The full-height interior changes the sauna experience. You can stand up to shower off between sessions, and the vertical wall lets you fit a wall-mounted backrest so tall users aren't compromised by the barrel curve.
It's a modular product, the base spec is what you see, but panel sizes, glass layouts, bench configurations and finishes can all be tailored at order. We handle the bespoke consultation in our design service.
Best for
Who typically buys this one.
- Design-led garden schemes where the sauna is an architectural feature
- Buyers who want a fully-insulated sauna for lower running costs
- Owners over 6' who find barrel ceilings restrictive
- Clients wanting a bespoke interior layout or non-standard dimensions
Real installations
Celsium Herkus L in Scottish gardens.
Every photograph on this page is a genuine Signature Garden Rooms installation.
Three reasons: (1) insulation, modular holds temperature far better, lower running cost; (2) architectural fit, cubes sit square into modern garden schemes; (3) headroom, 2.1m ceilings mean tall users aren't stooped. Barrels are cheaper and heat faster; the choice depends on how much you'll use it and how it sits in the garden.
Next step
Ready to talk about the Celsium Herkus L Modular Sauna?
Tell us your garden, your access, and roughly when you'd like it in. We'll come back with a considered price, honest lead time, and any planning notes for your site.
Fully insured · £5m public liability · Falkirk-based, working across Central Scotland