Services coordination for saunas and steam rooms: a guide for architects and builders

The short answer

Services for a sauna or steam room are driven by the equipment. Once the heater or steam generator is nominated, its installation manual sets the electrical supply, sensor and control positions, ventilation arrangement, water and drainage needs, plant-room limits and lighting constraints. Every trade works from that data.

• Nominate equipment early, at schematic design or early design development, and get the current manuals.
• Issue the requirements to each consultant and trade before services are documented.
• Fix every rough-in position before linings, because sauna foil and steam-room membranes are sealed around them.
• Use licensed trades for electrical, plumbing and waterproofing work, and involve the certifier early.

This guide focuses on information flow between trades. For room dimensions, build-ups, structural allowances and a full design-stage checklist, see our sauna and steam room design checklist.

What each trade needs, and when

Electrical

These are considerations only. All fixed wiring is designed and installed by a licensed electrician to AS/NZS 3000 and the manufacturer’s data.

Supply. Sauna heaters and steam generators are large fixed loads. Australian supply is nominally 230 V single-phase and 400 V three-phase (still often called 240/415 V). The supply is designed by the electrician from the selected model’s data: output, voltage and phase exactly as the manufacturer publishes them. Some smaller heaters come in single-phase versions, depending on the model; larger heaters commonly need three-phase, and larger outputs can need a separate power or contactor unit as well as the controller. Confirm early that the site supply can carry the load, alongside any other wellness equipment such as cold plunges or pool heating.

One heater per sauna room. Harvia’s heater manuals, including those for its commercial heaters, allow only one electric heater in a sauna room. A large room gets one correctly sized heater, with an external power unit where needed, rather than two smaller heaters. Some other manufacturers allow several heaters under conditions, so the selected heater’s manual governs. Settle this before the supply is designed, because it changes the number of circuits and the control arrangement.

Power and contactor units. A control switches only so much load. Above that, an external power unit or booster carries it: Harvia’s current power units switch 11 kW or 17 kW, with a booster adding more. The power unit needs its own wall position, generally outside the hot room in a dry place. Harvia’s Xenio power unit must not be recessed into a wall, because heat builds up behind it, while some splash-rated Fenix units may be fitted inside the sauna, low and well away from the heater. Show the position on the drawings.

Isolation and control locations. Controllers, power units and contactors are generally installed outside the hot room, in a dry position. In commercial rooms, controls often sit at an attendant desk or in a plant or utility space, and some generators can be switched on from reception. A steam control panel goes outside the steam room, in a dry area. Agree these positions with the designer so they appear on the drawings.

Sensors. Sensor positions follow the equipment drawing, because the control acts on what the sensor reads. In a sauna, Harvia places the room sensor at least 1000 mm from an omnidirectional supply vent, or 500 mm from a vent blowing away from it; a sensor in a draught makes the room run too hot or too cool. In a Harvia steam room, the sensor goes on the ceiling or on the wall at 1700–3000 mm, away from doors and vents. The ventilation and electrical designs therefore have to be read together.

Remote and timer start. If the owner wants app, timer or remote starts, the heater needs a safety device: a heater cover sensor above the heater that detects covering, or a magnetic door switch, unless the heater is certified to the covering test the control’s manual names. Only an electrician connects them. The door switch is wired into the door frame, so it has to be decided before the frame and linings go in.

Steam generators stay powered. Automatic draining and flushing run after the generator is switched off at its control, so the generator needs power after the session ends. The isolator is for servicing, not an everyday on/off switch, and its position and labelling should make that clear to the owner or operator.

Cable routes. Plan conduits for sensor, control and data cables from the room to the controller and power unit before lining. Manufacturers set cable lengths for sensors and controls, so the controller’s distance from the room matters. Keep power and control cables separate where the manufacturer requires it.

The sauna zones. AS/NZS 3000:2018 Electrical installations (known as the Australian/New Zealand Wiring Rules) includes a clause for saunas (clause 6.5) in its section on damp situations, with zones defined by distance from the heater. Equipment selection and position within the room follow those rules and the heater manufacturer’s requirements, as determined by the electrician.

Temperature-rated parts. The upper part of a sauna is far hotter than the lower part. One heater manufacturer requires cables above 1000 mm from the floor to withstand 170 °C and places the heater junction box no more than 500 mm above the floor; another requires all electrical installations inside the cabin to suit at least 170 °C. One manufacturer prohibits PVC-insulated cable to the heater because heat makes it brittle.

Residual-current protection. Safety-switch arrangements for the heater and other circuits are the licensed electrician’s decision under AS/NZS 3000 and the manufacturer’s instructions.

Commercial extras. Door sensors, emergency call points or steam-stop switches wired to a staffed point, timers, and building-management connections. Some controls offer KNX or Modbus gateways; confirm the protocol early. Check every device’s temperature rating against its position: one sauna and steam call point is rated to 65 °C.

Plumbing and drainage for steam rooms

These are considerations only. Plumbing and drainage are designed and installed by a licensed plumber under AS/NZS 3500 and the generator manufacturer’s manual.

Water supply. Each generator has its own pressure range, flow and connection requirements; isolation and backflow prevention are for the plumber. Steam generators appear in the WaterMark Schedule of Products, so confirm the status of the selected model. Water hardness matters: manufacturers set water-quality limits and recommend softening where water is hard. Test the supply, and allow space, power and drainage for a softener if one is needed.

Generator drain. Generators drain and flush, often automatically after each use. Harvia’s optional automatic discharge valve rinses the drain line on every fifth fill, can rinse the reservoir at set intervals during long institutional sessions, and drains and rinses for about five minutes after switch-off. The discharge is hot (about 70 °C in Harvia’s manual) and goes to a drain in the plant room, never into the steam room, with the pipe falling away from the generator. Large commercial units can discharge near-boiling water and may need tempering or a blowdown tank. Relief-valve outlets are piped as the plumber and manufacturer require.

Floor waste and falls in the steam room. The room needs a drain for condensate and cleaning, on a floor laid to fall, integrated with the waterproofing. For houses, the NCC Housing Provisions set the fall to a floor waste between 1:80 and 1:50 where one is installed; overseas steam-room details are often slightly steeper. Confirm falls with the hydraulic designer, waterproofer and certifier, and allow the slab or floor set-down at design stage.

Steam pipe. Plan a short, insulated route from the generator to the outlet, with a continuous fall and no low points where condensate can collect. Some manufacturers prohibit valves in the steam line. Maximum lengths and insulation ratings vary by manufacturer.

Steam outlet. The outlet sits low in the room, pointing down or away, out of reach of feet and hands, away from seating, the sensor and the door seals. Recommended heights range from about 100 mm to about 760 mm above the floor depending on the outlet design, and manufacturers disagree on whether it may sit under a bench. Use the selected manufacturer’s figure for the selected outlet.

Saunas. If a tap or sprinkler is wanted in a sauna, plumb it before lining and never position it over the heater. A combi heater with a water-connected evaporator, such as Harvia’s Virta Combi with automatic filling, needs a floor drain in the sauna or washroom in case of leaks. Sources differ on drainage: some recommend a floor drain, especially in commercial rooms, while one manufacturer prefers draining to a waste outside the room so a dry trap cannot let odours in.

Plant room and generator location

The generator’s location is one of the earliest decisions, because it fixes the steam pipe length, drainage and access.

• Inside, dry and protected. Generators go outside the steam room, in a dry interior space that cannot freeze, with a floor drain. One manufacturer specifies that the generator is not mounted directly above the drain, because rising steam wets the unit.
• Close to the room. Maximum steam pipe lengths in the documents reviewed range from about 5 m to about 18 m. Harvia prefers the generator as close as possible, under 6 m, with 10 m of well-insulated copper pipe as its maximum, laid to fall to the room with no extra bends or water pockets. Long or dipping pipes condense steam and can spit water at the outlet.
• Ambient temperature. Harvia limits the air temperature around the generator to 30 °C; other manufacturers set their own limits, such as 35 °C or 45 °C, and the selected model’s manual governs. Queensland roof spaces and unventilated cupboards can run hotter, so a ventilated plant cupboard or room is the safer allowance. A generator enclosed in a cabinet needs ventilation around it.
• Clearances and access. Use the clearances on the model’s drawing — one commercial range recommends about 610 mm around the unit. Allow access panels for drain valves, sediment traps, level sensors, pipe unions, softeners and contactor boxes, and a delivery route wide enough for the equipment. On Harvia generators the user empties the sediment cup, cleans the level sensor and descales, and the overheat reset button sits at the end of the unit under its cover; Harvia asks for a full service at least twice a year for generators in community or institutional use. A generator nobody can reach does not get serviced.
• Duty cycle. Commercial generators are chosen by hours of use and whether running is continuous or intermittent, not only by room size. Some systems link several generators to one control for capacity and backup, which also lets one be serviced while the others run.
• Security and separation. One commercial manufacturer strongly recommends a locked room not accessible to the public, away from pool-chemical storage.

Sauna power units and controllers also need a dry location outside the hot room, with a short, protected cable route.

Ventilation interface

The room’s ventilation arrangement comes from the equipment manual; the building’s ventilation comes from the mechanical engineer. They have to meet.

• Saunas. Manufacturers publish different inlet and exhaust layouts and air-change rates (Harvia about six an hour; Finnish guidance about three to six). Give the mechanical engineer the positions, opening sizes and rates from the selected heater’s manual, together with any drying vent.
• Steam rooms. Some manufacturers design for a sealed room during use, with exhaust or drying afterwards; others design for controlled supply and exhaust while the room runs. The generator is sized differently for each, so the approach must be settled before the generator is sized. One manufacturer makes mechanical ventilation mandatory for public steam rooms.
• Discharge and pressure. Agree where hot or humid exhaust air goes — not into a ceiling void — and how the sauna or steam room sits within the building’s pressure regime. One sauna heater manufacturer warns that building exhaust can reverse a naturally ventilated sauna’s airflow.
• Plant-room heat. Generators and power units give off heat. Ventilate or cool the plant space to keep it within the manufacturer’s ambient limit.

Any fan or damper in the hot air path needs a rating suited to the exhaust temperature; obtain that data from the component manufacturer.

Waterproofing interface

In Queensland, waterproofing is a separate QBCC licence class, and most building work valued over $3,300 (labour and materials) needs a QBCC-licensed contractor. The NCC 2022 wet-area provisions do not name saunas or steam rooms, so how a steam room is treated, and whether AS 3740:2021 Waterproofing of domestic wet areas applies to it, are questions for the building certifier.

For coordination, three points matter:

• Every service passes through the vapour layer. In a steam room, the steam outlet, sensor, lights, drain, valves and door frame all penetrate the membrane, and each must be sealed vapour-tight with products compatible with the system. Some systems require a specific heat-resistant sealant at the steam inlet. Positions must therefore be final before the membrane goes on.
• One documented system. The board, membrane and sealants should come from one manufacturer’s steam-room system, installed to its instructions by the licensed waterproofer.
• Sauna foil meets the floor waterproofing. In a sauna, one manufacturer laps the taped foil vapour barrier down onto the floor waterproofing, so the two trades’ work overlaps at the base of the wall.

Agree a hold point before linings or tiling, so penetrations, membranes and flood testing (where required) can be inspected and photographed.

Glazing interface

The Australian Standard for glass is AS 1288:2021 Glass in buildings – Selection and installation. Glass type, thickness and fixing are for the glazier, door manufacturer and certifier.

Glazing also affects the services. Large glass areas increase the required heater or generator output, so areas need to be known before equipment is sized. Sauna glass gets hot to the touch. In steam rooms, manufacturers differ on a gasketed door versus a deliberate gap under the door, and the choice must match the generator’s ventilation approach.

Lighting

Lighting in hot and wet rooms is selected for its temperature and moisture environment, and installed by a licensed electrician to the luminaire manufacturer’s instructions.

• Saunas. Temperature is the governing constraint. One manufacturer’s sauna lamp is rated for 125 °C ambient; its LED strip is rated to only 60 °C and must stay below 1600 mm from the floor. Lights placed low last longer, and under-bench lighting is a common choice. Do not place fittings over the heater, and keep drivers and transformers in a position the manufacturer permits. One manufacturer warns that protective light covers fixed directly against the wall or ceiling may be a fire risk.
• Steam rooms. Moisture and corrosion are the governing constraints. Fittings must be suitable for saturated air, sealed into the vapour layer and corrosion-resistant; manufacturers cite IP65 and IP67. Pool lights that rely on water for cooling may not suit.

Sequencing by project stage

Concept and schematic design

• Room type, use (residential or commercial), capacity and location fixed.
• Plant space located within likely steam pipe limits, with drainage and ventilation.
• Early electrical load advice and site supply capacity checked.
• Specialist engaged.

Design development

• Heater or generator nominated and current manuals issued to all consultants.
• Electrical: supply, circuits, isolation, controller and contactor positions, sensor and control conduits, lighting, fans and alarms documented by the electrical designer.
• One heater per sauna room confirmed against the heater manual; power-unit position, sensor positions and any door switch for remote start shown on the drawings.
• Hydraulic: water supply, softener, generator drain, auto-drain discharge route, relief outlets, steam pipe route, outlet position, floor wastes and falls.
• Mechanical: vent positions and rates, steam ventilation approach, discharge points, plant-room cooling.
• Structure: equipment weights, benches and glass issued.
• Glazing areas confirmed and fed back into equipment sizing.
• Waterproofing system nominated; certifier consulted on the steam-room pathway.

Documentation

• Rough-in drawings showing every penetration, conduit, drain and vent.
• Specification sections coordinated across trades; responsibilities agreed in the contract.

Framing and rough-in

• Set-out checked against the equipment drawings; noggins and backing in place.
• Conduits, drains, steam pipe and vent openings installed and checked.
• Hold point: rough-in inspection before any insulation, foil, board or membrane.

Linings and waterproofing

• Sauna foil continuous and taped around every penetration.
• Steam membrane installed, penetrations sealed, flood test where required, photographs taken.
• Hold point: waterproofing inspection before tiling.

Fit-off and commissioning

• Equipment, lighting, sensors and controls installed; electrician and plumber connect and test.
• Ventilation balanced; generator drain and flush settings confirmed.
• Settings recorded, manuals and certificates collected, operators trained.

What we provide to the design team

We size and select heaters, steam generators and controls from manufacturer data as part of each room’s design, and our team builds the room in coordination with the builder and licensed trades. As part of that, we can pass the design team:

• the provisional heater or generator selection and sizing
• the selected equipment’s published electrical, water, drainage and ventilation requirements, for the services engineers and trades
• equipment weights for the structural engineer
• the manufacturer’s plant-room, clearance and access requirements.