Sauna controls and contactor boxes, explained

An electric sauna heater needs three things to run safely: power, a control that decides when and how hot it runs, and a heavy-duty switch that can carry the heater’s current. Some heaters have the control and the switch built in. Most need a matching control kit, and a few need an extra box. Here’s how to tell which is which before you order.

The parts, in plain language

• Control panel: the keypad or dial where you set temperature and time. Wi-Fi versions add phone control.
• Sensor: mounted inside the hot room. On Harvia’s Xenio and Fenix systems, the heater sensor holds both the temperature sensor and the overheat protector.
• Contactor (power unit, relay box): a heavy-duty switch that turns the heater’s 240 V power on and off when the low-voltage control tells it to. Harvia calls it a power unit. Homecraft calls it a relay contactor box, with a 24 V transformer and a magnetic contactor inside. HUUM builds it into the UKU main module.

Which heaters need what

Homecraft’s TKE2-3 is the 208 V three-phase version, meant for buildings with three-phase power.

Why controls are brand-locked

We only pair heaters with controls from the same maker: Harvia with Harvia, HUUM with HUUM’s UKU, and Homecraft with Homecraft’s TKE controls. Each brand calibrates its sensor to its own control, and the wiring and communication between the parts differ. Because the sensor also carries the overheat protection, mixing brands breaks the safety chain the maker designed.

Match the control to the heater’s size

• Harvia: Harvia rates the Xenio CX30 and Fenix FX30 for 7 kW at 240 V on one supply circuit, or 11 kW when the heater is fed as two groups on two circuits. The Xenio CX45 and Fenix FX45 are rated for 10.8 kW on one circuit, or 17 kW on two. The heater’s manual shows which control and wiring to use.
• HUUM: the UKU main module handles heaters up to 11 kW, which covers every HUUM electric heater up to 10.5 kW. Above that, add the UKU Extension Box.
• Homecraft: the TKE2-2 covers 240 V single-phase Homecraft heaters up to the 10 kW Apex. The 12 and 15 kW Apex models use the TKE3.

Where the contactor goes, especially outdoors

Every maker puts the control electronics outside the hot room. For a backyard sauna, the brands differ in how much cold and weather they tolerate.

• Harvia Xenio and Fenix: Harvia says to mount the power unit outside the sauna room, in a dry place above 0 °C, and not to use it outdoors without a cover. In a Canadian winter, that usually means the house, a heated garage or another space that stays above freezing.
• HUUM UKU: the main module goes outside the sauna room in a weatherproof housing, and HUUM rates it to work down to −40 °C, though the display may slow in extreme cold. The control panel mounts at eye level beside the sauna door. If the panel is outdoors, HUUM recommends a protective box.
• Homecraft: choose the indoor relay box for basements, garages and utility rooms, or the outdoor version, which comes pre-mounted in a weatherproof enclosure. Homecraft’s manual calls for watertight fittings, with all cable entering through the bottom of the box.

Distance matters as well. Harvia and HUUM both limit the sensor cable between the hot room and the power unit or main module to 10 m (about 33 ft), so a box mounted in the house only works if the sauna is close enough. Tell us where the box will live before you order, and we’ll confirm the right version.

Wi-Fi control: what to know

• HUUM UKU Wi-Fi works with the HUUM app and connects only to 2.4 GHz networks.
• Harvia Xenio Wi-Fi and Fenix work with the MyHarvia app. Harvia lists Fenix remote control “with the MyHarvia Control Upgrade”, so ask us what’s included for your model.
• Homecraft offers Wi-Fi versions of its TKE2 and TKE3 controls.

Quick checklist before you order

1. Does the heater have built-in controls? If yes, you don’t need a separate control.
2. Is the control the same brand as the heater? It has to be.
3. Is the control rated for the heater’s kW at your voltage?
4. Does the heater need an extra box, such as the HUUM UKU Extension Box or the Harvia LTY45?
5. Where will the power unit or relay box go, and how cold does that spot get in January?
6. Do you want Wi-Fi, and does your signal reach the sauna?
7. What power does the building have? Homecraft notes that most homes have 240 V single-phase, while some commercial and multi-unit buildings only offer 208 V three-phase.

Next steps

• Browse sauna controls and contactor boxes.
• Still choosing a heater? Start with the heater size guide or the Heater Finder.
• Planning the wiring? Hand your electrician our Ontario electrical checklist.
• When you send an order request, we confirm that the heater, control and any extra box match the manufacturer’s documents before we invoice you. You pay nothing until you approve.