The short answer
A sauna control does four jobs: it sets and holds the temperature, limits how long the heater runs, cuts the power if anything overheats and, on most separate units, switches the lights and fan. Remote and app start add a fifth job: making sure the heater cannot start with a towel on it or the room unchecked.
The control and the heater are designed as a pair. The heater’s manual lists which controls it may be used with, and the control’s manual sets where the sensor, panel and power unit go. The manuals for the selected heater and control govern every detail. This guide explains the principles, using Harvia’s published guidance first and noting where other manufacturers differ.
Built into the heater, or a separate control unit
Many heaters come in two versions. Harvia sells, for example, the Vega BC60 with switches on the heater and the Vega BC60E for use with a separate control unit. Some newer Harvia heaters (XE, XW and FC models) are supplied with their own stand-alone panel.
| Controls on the heater | Separate control unit | |
|---|---|---|
| Where you adjust it | On the heater, inside the hot room | A panel on the wall, usually outside the room |
| Temperature setting | Mechanical thermostat dial | Digital set point, read from a sensor in the room |
| Timer | Mechanical. Harvia’s built-in models run for up to 4 hours, or can be pre-set up to 8 hours ahead | Digital on-time and pre-set timers, with limits set at commissioning |
| Remote or app start | No | Available on some systems, only with the safety devices the manual requires |
| Lights and fan | Wired separately | Usually switched by the control |
| Overheat protection | In the heater, reset inside its connection box | In the sensor box or as the manual describes |
| Large outputs | Limited to the heater’s own switching | Power units and extensions switch larger heaters |
| Suits | Simple home saunas, cabins, outdoor rooms with straightforward use | Premium homes, rooms with glass, app control, all commercial rooms |
Why this matters: a built-in control is simple and robust but sits in the heat, and you have to open the door to change anything. A separate unit costs more and needs its panel, power unit and sensor positions planned with the room, but it gives finer temperature control, outputs for light and ventilation, and the safety logic that remote start requires.
A practical tip from Harvia’s manuals for built-in thermostats: start at maximum and turn the dial down once the room is hot. Small movements near the top of the scale make a big difference.
The parts of a separate system
A separate control is usually three components:
- The control panel: the display and buttons the bather uses.
- The power unit: the box that actually switches the heater’s elements, lighting and fan. Harvia’s Xenio power unit goes outside the sauna, in a dry place above 0 °C, and must not be recessed into the wall because heat would build up around it. Harvia’s current Fenix and Xenio 110 and 110C power units may also be mounted inside the sauna, low on the wall (no more than 400 mm above the floor and at least 1,000 mm from the heater), which Harvia pitches for outdoor saunas. The larger 170 unit must be outside.
- The sensor box: the temperature sensor in the room, which on Harvia’s Xenio also contains the overheat protector.
Why this matters: each part has its own position rules and its own cable runs back to the power unit, so the electrician, builder and lining contractor need the layout before the walls are closed.
The temperature sensor is a safety item
The control only knows what its sensor tells it. Put the sensor in the wrong place and the heater either overruns or never gets the room up to temperature.
Harvia’s placement for its Xenio control:
- above a wall-mounted heater, on its centre line, about 100 mm below the ceiling;
- for a floor-standing heater, on the ceiling about 100–200 mm out from the heater’s side line;
- at least 1,000 mm from a supply vent that blows in all directions, or 500 mm from one directed away from the sensor.
Why it is a safety item, not just a comfort setting:
- Cool air on the sensor makes it read low. The control then keeps heating while the real room temperature climbs. Several manufacturers give the same 1,000 and 500 mm vent distances for this reason.
- A sensor too far from the heater misses the heat. On many controls the overheat protector sits in the same box. If the box is in a cool corner, the protector cannot see the heater overheating.
- A displaced or damaged sensor is one of the causes Harvia lists for overheat trips.
Some manufacturers offer a second sensor above the back bench for very large rooms, so the display shows the temperature where people sit. In those systems the sensor near the heater stays in charge of safety. One manufacturer lists a bench sensor fitted at bench height or under a bench as a fire-risk planning error, because the control can keep heating while only the safety limiter stands between the heater and the room.
Not every heater follows the same rule. One maker whose heaters circulate air with a fan says its sensor must not go above the heater at all. The sensor is always positioned to the selected heater and control manuals.
Overheat protection, and who resets it
Every sauna heater relies on an overheat protector (also called a safety limiter or high-limit cut-out). If the room or heater gets dangerously hot, it cuts the heater’s power and keeps it off until it is reset.
Where it is (Harvia): on heaters with built-in controls, the reset button is inside the heater’s connection box. On E models, the protector is in the control’s sensor box.
Who resets it: Harvia says only a person authorised for electrical work may reset the protector, unless the manual says otherwise, and only after the cause has been found. It is not a homeowner task.
What usually causes a trip (Harvia’s checklist):
| Cause | Why it overheats |
|---|---|
| Crumbled or tightly packed stones | Air cannot flow through the heater, so the elements and casing run hotter |
| Heater left on for a long time without use | Heat builds up with no door opening or water throws to take it away |
| Sensor moved, damaged or badly placed | The control misreads the room temperature |
| Heater knocked or shaken | Stones or elements may have shifted |
Why this matters: resetting without fixing the cause means it trips again, or worse, keeps overheating parts that were never designed to run that hot. Our sauna stones guide explains why stone condition is so often the culprit.
BSC Wellness works with a dedicated electrical contractor, an independent business and a Harvia-authorised service agent, who carries out our electrical servicing. If your heater has cut out, see our service page or contact us.
Heating-time limits
A sauna control limits how long the heater can run in one go. The limit is not a fault; it stops a heater running for hours in an empty room.
Manufacturers set these limits by referring to the international safety standard for sauna heaters, IEC/EN 60335-2-53, and they set different limits for different uses. Harvia’s published settings:
| Use | Harvia’s settings | Conditions |
|---|---|---|
| Heater with built-in timer | Up to 4 hours on | Mechanical timer on the heater |
| Family sauna (Xenio) | 1–6 hours | Factory limit for home use |
| Public sauna in an apartment building (Xenio) | 1–12 hours | Longer only after consulting Harvia |
| Commercial (Fenix, Spirit FC) | Selectable at 12, 18 or 24 hours | Set at commissioning for commercial use |
| Beyond the factory timer | No limit | The heater must be constantly supervised. In a public sauna without a timer, an “on” light must be visible where the heater is controlled from |
Other manufacturers follow a similar pattern but differ in detail. Several limit private saunas to 6 hours with no automatic restart, allow about 12 hours in hotels and apartment buildings, and reserve 18 to 24 hours for public saunas, set by the installer at commissioning. One requires the elements in a public sauna to be off for at least 6 consecutive hours in every 24 unless the room is supervised. These are manufacturers’ settings under a European product standard, not Australian regulations.
Why this matters: a venue that runs long days needs a control configured for commercial use, with supervision and indicator arrangements to match, rather than a home control being restarted over and over. Our commercial guide covers operating hours and supervision.
Remote, app and delayed start
Starting a sauna from a phone, a timer or a building system means nobody is standing at the heater when it switches on. A towel left draped over the stones is a fire risk. That is why manufacturers allow remote start only with a safety device.
Harvia’s rules (from its Xenio WiFi and Fenix manuals, citing IEC/EN 60335-2-53):
- Remote, app or pre-timed start is allowed only if a heater cover sensor above (or built into) the heater, which detects covering, or a magnetic door switch is fitted. Only an electrician may connect them.
- Harvia’s manuals call the cover sensor a “safety switch”. It is a different device from the electrical safety switch (residual-current device) in your switchboard, which is a matter for your electrician.
- The current Fenix and Xenio power units may also control heaters certified to the standard’s covering test without an extra switch. Other heaters still need a cover sensor or door switch.
- With a door switch, remote mode is armed by holding the heater button for 3 seconds. A 30-second delay lets you close the door. Opening the door cancels remote mode. A panel lock also blocks remote start.
- After the heater switches off, a 6-hour rest stops any timed, weekly or remote start until it has passed.
- The Xenio WiFi weekly timer may only be used in public saunas.
- The Spirit FC heater has an integrated cover sensor, but remote use stays disabled until it is set up.
- Check the room and the area around the heater before switching on, before a remote start and before leaving the control on standby for one.
| Safety arrangement | What it detects | Notes |
|---|---|---|
| None | Nothing | Remote and timed starts stay disabled |
| Door switch | Whether the door has opened since the room was checked | Opening the door cancels the armed start |
| Cover sensor over the heater | Something lying on or covering the heater | Fitted above the heater, connected by an electrician |
| Integrated cover sensor | Covering, built into the heater | Harvia Spirit FC; still needs setting up |
| Heater certified to the covering test | Designed to tolerate covering under the test | Only where the control’s manual allows it |
Other manufacturers apply the same principle with their own details. Some require the control to be re-armed by hand after every remote cycle.
Why this matters: app start is a real convenience, but only the safety device makes it safe. It has to be chosen with the heater and wired in when the room is built, not added as an afterthought.
Large heaters: power units and extensions
A control unit can only switch so much load itself. Larger heaters use an external power unit or contactor box that switches the elements on the control’s command.
Harvia’s examples:
- The Xenio CX110 control unit runs heaters from 2.3 to 11 kW.
- The current Fenix and Xenio 110 and 110C power units switch 11 kW over three circuits, and the 170 switches 17 kW. The 110C adds an output for a combi heater’s steamer.
- The LTY17 power extension adds another 17 kW of switching for larger heaters.
Other manufacturers’ controls typically switch around 9 to 10 kW themselves and add contactor boxes beyond that. Their guidance on location is consistent: outside the hot room, indoors, in a dry and ventilated spot, never enclosed in panelling or a cabinet, and with access for service.
Why this matters: the power unit and any extension are part of the electrical design. They need a wall, ventilation and service access, and they should come from the control’s own matched system. One manufacturer warns that mixing third-party switching gear with a control unit can cause faults in safety-relevant circuits.
The supply, cabling and protection for the heater, power unit and control are determined by a licensed electrician from the manufacturer’s data.
Lights, fan, steam and infrared outputs
Separate controls usually switch more than the heater:
- Lighting and fan. Harvia’s Xenio and Fenix controls switch lighting and a fan (up to 100 W each). The fan can be set to keep running after the heater switches off.
- Drying after use. Xenio has a dehumidifying interval: after switch-off it holds the room at about 40 °C for 45 minutes with the fan running, to dry the timber. It can be stopped by hand but not remotely.
- Combi heaters. A heater with a built-in evaporator needs a control with a steamer output. On Harvia’s Xenio, the temperature and humidity settings together cannot exceed 140 (for example 60 °C and 80 % relative humidity), and the steamer stops if the water runs out. See Choosing and sizing a sauna heater for how combi heaters work.
- Infrared. Harvia describes the heater and infrared panels in a hybrid sauna as controlled separately. Some controls elsewhere have an auxiliary output for infrared emitters; one Harvia-group control permits it only with emitters that have their own overheat cut-out. Whether both may run at once is set by the manufacturers of the exact heater, emitters and control. See Traditional, infrared or hybrid sauna?
What commercial controls add
Commercial rooms run longer, are used by strangers and are managed by staff, so their controls do more:
- Longer, supervised heating limits set at commissioning (see the table above), and a weekly timer where the manufacturer permits it for public saunas.
- User profiles. Harvia’s Fenix stores user profiles, and the Spirit FC ships with editable presets. Staff can set a few standard sessions instead of adjusting settings by hand.
- Panel lock or access control, so guests cannot change set points or start remote modes.
- Building management integration. Some control ranges offer a potential-free remote start input, a status output, or gateways to building automation protocols. Availability depends on the product, and remote operation still needs the safety devices described above. Confirm the protocol with the services engineer before equipment is chosen.
- Emergency stop. One Harvia-group manufacturer offers an emergency-stop button mounted beside the door, no higher than 100 cm, which breaks the control’s safety circuit and can trigger a horn or lamp so staff are alerted.
- Record the settings. Time limits, profiles and safety settings should be recorded at commissioning and kept with the operating manual.
Why this matters: a venue’s control is part of its safety and staffing plan. Settings chosen at commissioning decide how long the room can run, who can change it and how quickly staff hear about a problem.
Where the control panel goes
The panel’s manual sets where it may be mounted, and the rules differ between products.
- Outside the room is the simplest choice: the electronics stay out of the heat and bathers can see the status before they open the door. One manufacturer recommends the hinge side of the door, so hot air escaping when the door opens does not condense inside the panel.
- Inside the room is permitted for some panels, but only in zones the manual allows. One manufacturer, for example, requires an in-room panel to be no higher than 800 mm above the floor, at least 300 mm from the heater and where the air never exceeds 80 °C.
- The power unit has its own rules (above), and is usually outside the room.
- Steam rooms are different. Harvia’s steam generator panels must be outside the steam room, in a dry area. See steam room design and construction.
Why this matters: a panel in the wrong place overheats, collects condensation or is hard to read. Its position, and the cable route back to the power unit, should be on the drawings before the lining goes up.
Compliance and licensed trades
Controls, power units, safety and door switches, and their supply, cabling and protection must be installed by a licensed electrician to AS/NZS 3000 and the manufacturers’ installation manuals. Heating-time limits and safety settings follow the selected control’s manual. Overheat protectors are reset only by a person authorised for electrical work, after the cause has been found.
Questions to settle before choosing a control
- Does the heater have built-in controls, or does it need a separate control unit? Which controls does its manual list as compatible?
- Where will the sensor go, and is it clear of supply vents by the distances the manual sets?
- Will the sauna be started remotely, by app or by timer? If so, which cover sensor or door switch does the manual require?
- Is the room residential or commercial, and what heating-time limit and supervision arrangement follow?
- Does the heater’s output need a power unit or extension, and where will it be mounted?
- Which lights, fan, combi steamer or infrared outputs are needed, and does the control support them?
- Where will the panel go, and is that position permitted by its manual?
- For a commercial room: which profiles, locks, building-system links or emergency stop are wanted, and who records the settings at commissioning?
How we approach it
We select the heater and control together, from the manufacturer’s data, and plan the sensor, panel and power-unit positions with the room design so the electrician and builder have them early. Our heater guide explains how the heater itself is chosen.