By Matt Tomkin, Editor, SaunaCentral — updated 7 September 2026.
In short: A commercial sauna is one built for continuous public use rather than a household’s few sessions a week — typically 6–12 people, a 12–18kW heater on a 400V three-phase supply, and heavier-duty benching and controls. Expect £15,000–£60,000 installed in the UK depending on whether you fit out an existing room or bring in a ready-made cabin, and roughly £15–£25 a day in electricity for a full operating day.
The difference between a domestic and a commercial sauna isn’t really size. It’s duty cycle. A garden sauna heats up three times a week; a gym sauna runs from six in the morning until ten at night, seven days, with people opening the door every few minutes. That changes the heater, the wiring, the ventilation, the timber and the bench construction — and it’s why a scaled-up domestic cabin tends to fail within two years.
This guide covers what actually differs, the power supply question that stalls most projects, what UK venues pay, and the compliance side that a domestic buyer never has to think about.
What counts as a commercial sauna
There’s no legal definition, and plenty of suppliers sell “commercial” cabins that are domestic units with a bigger heater. The practical test is whether the specification assumes continuous operation. Four things separate the two:
| Domestic sauna | Commercial sauna | |
|---|---|---|
| Heater output | 4.5–9kW, single-phase 230V | 12–18kW, 400V three-phase |
| Duty cycle | 2–4 sessions a week | 10–16 hours a day, every day |
| Controls | Manual dial or basic timer | Programmable, remote or scheduled; often a mandatory cut-off timer |
| Benching | Single or two tier, light framing | Two or three tier, heavier framing, removable for cleaning |
| Ventilation | Passive inlet and outlet vents | Often mechanical, sized to occupancy |
The heater is the clearest signal. If a supplier is offering a 9kW unit for a ten-person room, the room will never hold temperature with the door opening constantly — and the heater will run at full draw permanently trying, which is how elements burn out.
The electrical supply is where most projects stall
This is the single biggest practical constraint on a commercial sauna, and it is worth resolving before you look at cabins at all.
Commercial-output heaters need three-phase power. Take the HUUM HIVE 18 as a worked example, because the manufacturer publishes its figures: an 18kW output requires a 3/N~400V supply, a 32A fuse and a 5 × 6mm² cable, and it is rated for rooms of 18–28m³. The same range at 12kW needs 400V and 20A. HUUM publish the full specification for each output.
The arithmetic explains why three-phase isn’t optional. An 18kW load on a single-phase 230V supply would draw around 78A — more than most domestic main fuses carry in total. Split across three phases at 400V it’s about 26A per phase, which a commercial supply handles comfortably.
What that means in practice:
- Most industrial units, leisure centres and larger hotels already have three-phase. Check the meter and the incoming cable before anything else.
- Many converted buildings, rural campsites, village halls and small high-street units do not. A new three-phase supply from the DNO commonly runs into four figures and can take several months, depending on how far the nearest network is.
- If three-phase isn’t viable, the realistic options are a wood-fired heater (no mains load, but a flue, fuel handling and staff time), or accepting a smaller room on a large single-phase heater — which caps you at roughly four to six people.
A commercial installation is not covered by Approved Document P, which applies to dwellings. It falls under the Electricity at Work Regulations 1989 and BS 7671, and it needs a qualified electrician with commercial experience — not a domestic installer.
Sizing and throughput
Capacity claims are usually generous. The workable rule is 0.6–0.8m² of bench per person for a venue where people expect to lie down or spread out, and closer to 0.5m² if you’re planning benches as seating only.
Throughput matters more than headline capacity. A typical user does 10–15 minutes, so a genuine eight-person room turns over roughly 25–35 people an hour at busy times. If your peak is a 6pm gym rush of 60 people, an eight-person sauna will have a queue regardless of how well it’s built.
| Heater output | Rough room volume | Realistic peak throughput | |
|---|---|---|---|
| 4–6 people | 9–12kW | 12–18m³ | 15–25 per hour |
| 6–8 people | 15kW | 15–23m³ | 25–35 per hour |
| 8–12 people | 18kW | 18–28m³ | 35–50 per hour |
Room volumes above follow the HUUM HIVE ratings, which are typical of commercial heaters generally. Every manufacturer publishes a minimum and maximum — undersizing the heater for the volume is the most common specification error, and oversizing it wastes electricity and scorches the timber.
Fit out a room, or bring in a finished cabin
Three routes, and the right one depends far more on your building than your budget.
| Bespoke fit-out | Modular cabin | Ready-made unit | |
|---|---|---|---|
| What it is | A sauna built into an existing room | Panels delivered and assembled on site | Complete cabin delivered finished |
| Typical cost | £20,000–£60,000+ | £15,000–£40,000 | £25,000–£60,000+ |
| Lead time | 3–6 months | 6–12 weeks | 4–12 weeks |
| Disruption | Highest — trades on site for weeks | Moderate — days on site | Lowest — craned or wheeled into place |
| Best for | Awkward spaces, listed buildings, a specific design | Regular indoor spaces with good access | Outdoor space, leased premises, testing a site |
| Watch out for | Cost creep once walls are open | Access routes for panel sizes | Craning costs, ground preparation, planning |
The ready-made route has grown quickly in the UK because it removes the construction risk. You are buying a finished product rather than managing a build — which matters if you’re on a lease and can’t justify permanent alterations, or if you want the option to move it later. The trade-off is that you need vehicle access and somewhere to put it.
What it costs to run
Electricity is the running cost that surprises people. Business electricity has sat broadly in the 25–30p per kWh range through 2026, though commercial contracts vary far more than domestic ones — check your own unit rate rather than trusting a generic figure.
An 18kW heater doesn’t draw 18kW all day. It draws close to full output during warm-up, then cycles thermostatically. A defensible estimate for a full operating day:
- Warm-up: roughly 45–60 minutes near full draw — call it 15–18kWh.
- Running: cycling at roughly 35–50% duty, so a further 12 hours costs around 75–110kWh — higher if the door is opening constantly.
- Total: around 90–130kWh a day, or £23–£39 at 26–30p/kWh.
Those are estimates from the heater rating and a duty-cycle assumption, not metered figures, and a well-insulated room at the lower end of the volume range will beat them. The point is the order of magnitude: budget £500–£1,000 a month in electricity for a hard-working commercial sauna, plus stones (replaced every 1–2 years under heavy use), element replacement, and cleaning.
Compliance, and what a domestic buyer never has to consider
This is the part most commonly underestimated.
- Planning permission. The permitted development rights people cite for garden saunas apply to dwellinghouses. A sauna cabin on commercial land is a different question, and you should assume planning permission is needed and confirm with your local planning authority. Fitting one inside an existing building usually doesn’t need permission, but a change of use might.
- Building regulations. Ventilation falls under Approved Document F for buildings other than dwellings, and accessibility under Part M. Fire compartmentation matters if the sauna sits within a larger building.
- Electrical. BS 7671 and the Electricity at Work Regulations 1989, certified by a competent commercial electrician.
- Insurance. Tell your insurer before installation, not after. Public liability cover often carries conditions on supervision, signage, maximum session times and a cut-off timer.
- Supervision and signage. No UK law sets a mandatory attendant, but your insurer and your risk assessment probably will. Clear rules on session length, alcohol, medical conditions and pregnancy are standard practice.
- Water systems. If you add showers or a plunge pool, legionella risk assessment under HSE’s ACOP L8 comes into scope. A dry sauna alone doesn’t.
Who builds commercial saunas in the UK
The UK market splits into three groups. Long-established spa contractors such as Oceanic Saunas (manufacturing since 1982) and Leisurequip handle large fit-outs and steam-room combinations. Craft cabin builders — Heartwood Saunas in mid-Wales, Sven Saunas in Bedford, Sauna Spec in Greater Manchester — take on commissioned commercial work alongside domestic builds. And a newer group sells finished, relocatable units, including Hot Blue in Liverpool — a SaunaCentral partner — whose Hot Box is an eight-person cabin on heavy-duty wheels, delivered fully assembled on an 18kW HUUM HIVE.
We don’t sell saunas, and we don’t take a view on which of these is “best” — it depends entirely on your building. Hot Blue is a commercial partner of SaunaCentral; everyone else here is named on editorial merit. See our affiliate disclosure. Our UK sauna builder directory lists installers by region and service, including those who take commercial commissions.
Commercial saunas we list
Frequently asked questions
How profitable is a sauna business?
It depends almost entirely on utilisation. The economics are straightforward: your main variable cost is electricity at roughly £23–£39 a day for a hard-running commercial unit, against whatever you charge. At £10–£15 a session, a sauna doing 20 paying sessions a day covers its energy several times over — but rent, staff and marketing are usually the larger numbers, and quiet weekday mornings are what kill margins. Venues that add a sauna to an existing membership (a gym, a padel club, a campsite) tend to do better than standalone sites, because the footfall is already there.
Do commercial saunas require planning permission?
Often, yes — and you shouldn’t rely on the permitted development rules that apply to garden saunas, because those cover dwellinghouses. Installing a sauna inside an existing commercial building generally doesn’t need planning permission, though it may need building regulations approval and could raise a change-of-use question. Putting a cabin outdoors on commercial land usually does need permission. Ask your local planning authority before you order anything.
What is the 200 rule in a sauna?
It’s an informal guideline from Finnish sauna culture: the temperature in °F plus the relative humidity in percent should total roughly 200 for a comfortable session. So 180°F (82°C) at about 20% humidity, or 160°F (71°C) at 40%. It’s a rule of thumb about the balance between heat and humidity rather than any kind of standard, and it’s useful mainly as a reminder that pouring more water on the stones means you should be running a lower air temperature.
Is it cheaper to build or buy a commercial sauna?
Buying a finished unit is usually cheaper than it first looks, because a bespoke fit-out carries the risks that a delivered cabin doesn’t — trades on site, unexpected structural work, and a programme that slips. A modular panel system is typically the lowest headline cost for a regular indoor room with good access. A bespoke build makes sense when the space is awkward, the building is listed, or the design genuinely matters commercially. What is almost never cheaper is a DIY build using domestic components: the heater won’t cope with the duty cycle, and your insurer will want certification you can’t produce.
Related
If the unit needs to move between sites or you’re buying to rent out, start with mobile saunas. For the domestic end of the market see outdoor saunas and home saunas, and for what installation involves generally, how much a sauna costs in the UK.