Commercial Sauna Electrical & Ventilation Planning in Hong Kong: Zones, RCDs, Airflow and MEP Coordination

A common specification shortcut is to choose a heater from room volume and then solve everything around it.

That can be backwards.

Before heater selection is frozen, the project team should confirm:

• internal sauna dimensions and ceiling height;
• timber, glass, masonry and insulated surfaces;
• heater location and required clearances;
• control-panel location;
• temperature-sensor position;
• electrical supply and protective-device strategy;
• cable and accessory locations relative to sauna electrical zones;
• ventilation inlet and outlet arrangement;
• door position and under-door air path, where relevant;
• maintenance and replacement access; and
• intended operating hours and commercial duty cycle.

The final heater model should be the result of those coordinated inputs, not the starting assumption.

EMSD’s 2025 Code does not treat a sauna as an ordinary dry room.

Code 26L defines three zones around the heater and room. [1]

Zone 1 — the heater zone

Zone 1 contains the sauna heater. In the Code, its horizontal boundary is generally a vertical surface 0.5 m from the heater surface, unless the heater is closer than 0.5 m to a wall, in which case the cold side of the wall insulation becomes the boundary. [1]

The design implication is straightforward: the heater position influences the electrical zoning of the room.

Moving the heater late in the project can therefore affect more than timber detailing. It can change how nearby electrical components and wiring need to be reviewed.

Zone 2 — the lower room zone outside the heater zone

Zone 2 is the volume outside Zone 1 from the floor up to 1.0 m above the floor. [1]

Zone 3 — the upper room zone

Zone 3 is the upper volume outside Zone 1, above the 1.0 m level and bounded by the cold side of the room’s ceiling and walls. [1]

These zone descriptions are not a substitute for the full Code. They are a coordination warning: equipment location, cable routing and control placement should be checked against Code 26L before architectural finishes make changes expensive.

Sauna electrical discussions often become misleading when the RCD requirement is reduced to one sentence.

The 2025 EMSD Code says that additional protection should be provided for sauna circuits by one or more RCDs with the characteristics referenced in Code 11J. It then makes an important distinction: RCD protection need not be provided for the sauna heater unless the manufacturer recommends it. [1]

That means neither of these simplified statements is reliable:

“Every sauna heater in Hong Kong must have an RCD.”

or:

“Sauna heaters do not need RCD protection.”

The correct design decision depends on the local Code wording, the heater manufacturer’s requirements and the project electrical design.

For a commercial project, this is exactly the type of point that should be resolved between the sauna supplier, MEP consultant and registered electrical contractor before equipment is ordered.

EMSD states that contractors engaged in electrical work on fixed electrical installations must be registered with EMSD, and that the work includes installation, commissioning, inspection, testing, maintenance, modification, repair, supervision, certification and design of fixed electrical installations. [2]

For a sauna project, this matters because the heater is only one part of the electrical scope.

The project may also involve:

• distribution-board capacity;
• final circuits;
• isolators;
• protective devices;
• control wiring;
• lighting;
• sensor wiring;
• relay or power-control equipment; and
• inspection, testing and certification before energisation.

Kung Sheung can coordinate sauna-system requirements and interfaces, but the fixed-electrical scope must still be handled through the applicable Hong Kong registered electrical contractor / registered electrical worker framework.

Room volume is important, but it is not the only sizing input.

Tylö’s current commercial product data shows why generic formulas can be misleading. Manufacturer room-volume ranges differ by model and power output. Examples in the Sense Commercial family include: [6]

• 6.6 kW: approximately 4–8 m³;
• 8 kW: approximately 6–12 m³;
• 10.7 kW: approximately 10–18 m³;
• 16 kW: approximately 15–35 m³; and
• 20 kW: approximately 22–43 m³.

Those figures are manufacturer model ranges, not a universal engineering law.

A room with large glazed areas, masonry, unusual ceiling height or different insulation performance may require different treatment in the manufacturer’s sizing process. Commercial operating patterns can matter as well.

The safer specification method is:

1. calculate the actual internal room volume;
2. identify glass area, masonry surfaces, insulation build-up and ceiling-height assumptions;
3. check the exact current manufacturer sizing method;
4. verify heater clearances and available installation position;
5. verify the associated control/relay equipment; and
6. coordinate electrical load with the project MEP design.

A sauna ventilation drawing should not be treated as a generic exhaust-air sketch added after the heater is chosen.

Tylö’s commercial installation guidance uses a specific natural-ventilation principle. For the documented Sense Commercial installation, the inlet is positioned through the wall under the centreline of the heater. The outlet is positioned high and as far as practical from the intake, returning air toward the same surrounding space from which the inlet receives air. [4]

Tylö’s broader sauna construction guide follows the same basic concept and gives product-range-specific opening guidance. [5]

The engineering lesson is not “every sauna must use this exact ventilation layout.”

The lesson is:

the ventilation strategy has to match the selected heater/control system and the actual pressure relationships around the sauna room.

If a project uses a different heater manufacturer or a mechanically assisted ventilation concept, the project team should validate that arrangement against the manufacturer’s current installation requirements and the wider MEP design.

Manufacturer manuals often include useful numeric guidance.

For example, Tylö documentation gives vent-opening areas for certain heater ranges, including approximately 125 cm² in some smaller-heater configurations and larger openings in higher-output configurations. [4] [5]

Those numbers should not be copied into a generic specification as though they were Hong Kong statutory ventilation limits.

They are manufacturer-specific installation data.

The correct project question is:

What ventilation arrangement does the exact selected sauna heater/control system require, and how will the building ventilation design support that airflow path?

Ventilation is not only about occupant air exchange.

Tylö specifically warns that incorrect ventilation can expose a control panel installed inside the sauna to excessive temperature, potentially causing deformation or failure. Its Sense Commercial installation manual states that the ambient temperature around the control panel should not exceed 80°C. [4]

That makes control-panel location a coordination item, not a cosmetic choice.

If manufacturer ventilation conditions cannot be achieved, the manual directs the panel outside the sauna cabin.

The same principle applies to temperature-sensor placement: the sensor must be positioned according to the manufacturer’s installation geometry so that the control system is measuring the thermal condition it was designed to regulate.

This is another area where simplified rules can cause problems.

Tylö’s guide recommends a self-draught / thermal ventilation approach for its documented sauna construction concept and cautions that mechanical exhaust directly from the sauna can be difficult to balance correctly. [5]

That is a manufacturer design approach, not a universal Hong Kong prohibition on mechanical ventilation.

Commercial projects may have larger building ventilation systems, pressure regimes, fire/smoke considerations and architectural constraints. The correct design therefore needs coordination between:

• the selected sauna manufacturer;
• the project MEP consultant;
• the specialist sauna supplier;
• the architect; and
• the contractor responsible for the surrounding ventilation system.

The important requirement is that the final airflow arrangement supports the heater manufacturer’s operating assumptions rather than fighting them.

A good sauna coordination drawing should resolve at least four items together:

Heater position

Confirm manufacturer clearances, guarding, access and the effect of heater position on Code 26L zoning.

Temperature sensor

Confirm the manufacturer’s exact sensor location relative to heater, ceiling and room geometry.

Control panel

Confirm whether the selected panel may be installed inside the sauna and, if so, under what ventilation and temperature limits.

Ventilation openings

Confirm inlet and outlet locations relative to heater, door, surrounding room and pressure path.

Changing one can affect the other three.

That is why a coordinated sauna shop drawing is more valuable than four separate equipment datasheets.

EMSD states that the 2025 Edition of the Code of Practice was published on 31 December 2025. EMSD also provides a one-year grace arrangement under which fixed electrical installations, or parts of installations, complying with the 2020 Edition are also deemed to meet the Wiring Regulations if completed and connected to electricity supplies on or before 31 December 2026. [1]

For projects that cross that transition period, the electrical consultant and registered contractor should confirm which edition is being applied to the relevant scope.

A sauna supplier should not make that legal/compliance determination alone.

Before heater procurement or tender close-out, the team should be able to answer the following.

Room and envelope

• What is the confirmed internal room volume?
• What percentage of the envelope is glazed, and what masonry surfaces and insulation build-up are proposed?
• Is the ceiling height within the selected manufacturer’s design assumptions?
• Are insulation and vapour-control details coordinated with the room build-up?

Heater and clearances

• What exact heater model and output are proposed?
• Is the manufacturer room-volume range appropriate after construction factors are considered?
• Are wall, ceiling, bench and guarding clearances shown on the drawing?
• Can the heater and stone compartment be serviced?

Electrical

• Has Code 26L zoning been overlaid on the room layout?
• Are final circuits and protective devices coordinated?
• Has the heater-specific RCD requirement been checked against both EMSD Code wording and manufacturer instructions?
• Is the control/relay equipment included in the electrical scope?
• Is the fixed-electrical work being handled under the appropriate REC/REW framework?

Controls and sensors

• Is the temperature sensor shown in the manufacturer-required location?
• Is the control panel location permitted for the selected system?
• If the panel is inside the sauna, are manufacturer ventilation and ambient-temperature conditions satisfied?

Ventilation

• Where is supply air introduced?
• Where is exhaust air removed?
• Does the airflow path pass through the room in the way the heater manufacturer expects?
• Are surrounding-room pressure conditions compatible with the design?
• If mechanical ventilation is proposed, has it been checked against the selected manufacturer’s installation requirements?

Handover and maintenance

• Are electrical test/certification requirements defined?
• Are heater, sensor, relay/control equipment and ventilation openings accessible for inspection?
• Are current manufacturer manuals included in the handover package?
• Are the operator’s cleaning, stone inspection and equipment-service responsibilities clear?

A commercial sauna project becomes easier to manage when responsibilities are explicit.

The heater manufacturer should define product-specific sizing, clearances, ventilation, sensor and control requirements.

The MEP consultant should coordinate electrical load, circuits, protective devices, ventilation interfaces and the wider building-services design.

The registered electrical contractor / worker should carry out and certify the applicable fixed electrical work under Hong Kong requirements.

The architect / interior designer should coordinate room envelope, door, bench, finishes, access and the spatial consequences of electrical zones and heater clearances.

The sauna specialist should connect those requirements into one coherent room-level design and flag conflicts before procurement.

Kung Sheung treats a commercial sauna as a coordinated thermal room rather than a stand-alone heater sale.

For hotels, private clubs, wellness facilities and premium residential projects in Hong Kong, Macau and the Greater Bay Area, our technical review can cover:

• heater and control-system fit;
• room-volume and construction assumptions;
• heater/sensor/control layout;
• electrical-zone coordination;
• ventilation interfaces;
• access and maintainability;
• drawing review; and
• coordination with the project’s architect, MEP team and electrical contractor.

The objective is to resolve the interfaces before they become site problems.

If a project team is still choosing equipment, the most useful information to send is the room plan, internal dimensions, sections/elevations, wall/glass build-up, proposed electrical supply, ventilation concept and intended operating profile.

That gives the design team enough context to review the sauna as a system rather than a catalogue item.