The UKU: Required to Run Any HUUM Electric Heater
Here's the first thing to know before you buy: a HUUM electric heater won't turn on without a UKU controller. HUUM builds it this way on purpose. The heater is the cage and the stones; the UKU is the brain that reads the room temperature, fires the elements, holds your set point, and shuts everything down on a timer. Decoupling the two means you get to choose how you interact with your sauna instead of being stuck with whatever panel the factory bolted on.
So every HUUM electric heater you see across the HUUM electric heater range — the Drop, the Hive, the Hive Mini, the Cliff, the Steel — needs exactly one UKU to run. The question isn't whether you need a controller. It's which UKU, and whether your heater is big enough to also need the Extension Box. That's what this page is for.
What the UKU Actually Does
The UKU is a digital thermostat and timer built specifically for HUUM heaters. It senses the sauna's temperature through a sensor mounted on the wall, runs the heating elements up to your target, and maintains it. You set the temperature and the session length; the UKU does the rest. On the WiFi versions, it also talks to the HUUM mobile app so you can preheat the room from your phone on the drive home and walk into a sauna that's already at 190°F.
One control unit drives one heater. The temperature sensor and the wiring to the heater are part of the install, which a licensed electrician handles alongside the heater's dedicated circuit. The UKU itself mounts outside or just inside the sauna door, depending on the model.
UKU Local vs. WiFi vs. Glass vs. Mirror
UKU Local — wired, no internet
The UKU Local is the straightforward one: a wired wall panel with a dial and display, no WiFi, no app. You walk up, set your temperature and timer, and go. Pick this if you don't want your sauna on the internet, if your install spot has no reliable WiFi, or if you just don't care about preheating from your phone. It comes in Black, White, and Wood finishes. It does everything a sauna controller needs to do — it just doesn't talk to anything.
UKU WiFi — adds the HUUM app
The UKU WiFi is the same controller with connectivity added. Through the HUUM mobile app you can preheat remotely, schedule recurring sessions (every weekday at 6am, say), and check the room status from anywhere. This is the one most home buyers choose, because the single biggest friction point with a sauna is the 30–40 minute warm-up — and being able to start it from your phone erases that. Also available in Black, White, and Wood.
UKU Glass and UKU Mirror — the design versions
The UKU Glass and UKU Mirror are the WiFi controller wrapped in a premium finish. Same app, same scheduling, same remote preheat — the difference is purely the face. UKU Glass is a clean glass front; UKU Mirror is a reflective mirror finish that disappears into a minimalist wall when it's off. If the controller is going somewhere visible and you care about the look, these are the upgrade. If it's tucked in a back hallway, save the money and get the standard WiFi.
Which Heaters Need the UKU Extension Box
Most HUUM heaters run on the UKU alone. But the largest ones pull more load than the base control unit can switch directly. Any HUUM electric heater over 12kW — specifically the HUUM Hive at 15kW and 18kW — also requires the UKU Extension Box, a contactor module that sits between the UKU and the heater to handle the higher amperage.
The rule is simple: 12kW and under, the UKU is all you need. Over 12kW, add the Extension Box. The 12kW Hive sits right on the line and does not require it; the 15kW and 18kW do. Every other HUUM line — the Drop (max 9kW), the Hive Mini (max 10.5kW), the Cliff (max 10.5kW), the Steel (max 10.5kW) — stays under the threshold and runs on the UKU by itself.
Compatibility Across the HUUM Lineup
Any UKU version works with any HUUM electric heater — the Local, WiFi, Glass, and Mirror are interchangeable from a compatibility standpoint. You're not matching a specific UKU to a specific heater; you're choosing your interface and finish, then adding the Extension Box only if your heater is over 12kW.
That means a HUUM Cliff buyer who wants the app gets the UKU WiFi. A HUUM Steel buyer on a budget who doesn't need connectivity gets the UKU Local. A 15kW Hive buyer who wants the mirror look gets the UKU Mirror plus the Extension Box. The controller decision and the heater decision are independent — pick each on its own merits. If you'd rather not source them separately, our HUUM electric heater packages bundle the heater with your choice of UKU and the stones in one order.
How to Choose Your UKU
Start with one question: do you want to control the sauna from your phone? If no, get the UKU Local and you're done — it's the simplest, least expensive option and it does the core job perfectly. If yes, you want a WiFi version, and the only remaining decision is finish. Standard WiFi (Black/White/Wood) if the controller is out of sight or you want to keep cost down. Glass or Mirror if it's mounted somewhere visible and the look matters to you.
The remote-preheat feature on the WiFi models is the one that changes how often people actually use their sauna. A heater that takes 35 minutes to warm up is a heater you have to plan around. A heater you start from your phone before you leave work is one that's ready the moment you walk in — and that's the difference between a sauna you use twice a week and one you use every day. For most home builds, that alone justifies the step up from Local to WiFi.
Installation and What to Order Alongside
The UKU ships with its temperature sensor and mounting hardware. The control unit, the sensor, and the wiring back to the heater are all part of the electrical install, which has to be done by a licensed electrician — the same person wiring the heater's dedicated 240V circuit can mount and connect the UKU at the same time. Our sauna electrical requirements guide covers the rough-in details so your electrician has what they need before they show up. Always consult a licensed electrician before any electrical work; requirements vary by local code.
If you're sourcing parts à la carte, plan on heater + UKU controller + sauna stones as your minimum order — and add the Extension Box if your heater is a 15kW or 18kW Hive. If app control is a must-have for you, our WiFi-enabled heater collection gathers every heater that pairs with a WiFi controller in one place. HUUM's warranty on the UKU runs alongside the heater warranty and is valid only through authorized dealers like Topture — we're an authorized HUUM dealer, ship free, and our team's around if you hit a question during install.
