HUUM Rebuilt Its App From Scratch. The Biggest Change Is One You Cannot See.

HUUM has released App 4.0, and the Estonian heater manufacturer is not being coy about the scope: this is a complete rebuild, not an update. New mobile client. New server infrastructure. New communication pipeline between phone and wall panel.

“This wasn’t a patch or a polish,” HUUM told SaunaNews directly. “This is a serious piece of engineering, built to serve you faster, more reliably, and at a scale ready for everything that comes next.”

The app, now called HUUM Sauna Control, went live on iOS and Android in mid-June 2026. Version 4.0.2 is the current release. It is a free download for anyone with a HUUM UKU WiFi or UKU 4G controller.

The Biggest Change Is One You Cannot See

HUUM is leading with an unusual admission: the most important part of the new app is invisible.

“Behind this new app is something you’ll never tap, swipe, or open, and that’s exactly the point,” the company wrote in its announcement. “HUUM has grown. A lot. So much, in fact, that we rebuilt our entire server infrastructure from the ground up. Every part of the engine that connects your phone to your sauna.”

“You won’t see it. You’ll feel it in every single tap.”

The concrete claim: 3x faster communication between the app and the UKU control panel. HUUM says every command now responds instantly, with no delay between tap and heat.

That speed matters most for remote start. When you are driving home and want the sauna warm by the time you walk through the door, the difference between a three-second lag and a one-second lag is the difference between trusting the app and walking over to the wall panel.

Multi-Sauna Support Is the Commercial Play

The headline consumer feature is smarter booking: set the day, time, temperature, and duration in seconds, save recurring sessions, and keep the next booking visible on the home screen. HUUM says the goal is that “your sauna is ready before you walk through the door.”

But the feature that matters most for operators is multi-sauna management. App 4.0 lets a single user view and control every HUUM-equipped sauna from one screen, with current temperature, target temperature, status, and alerts for each unit visible at a glance. “Online, offline, or heating,” HUUM writes, “you always know where things stand.”

For a homeowner, that is a nice-to-have. For a hotel, gym, or spa operator running three or four HUUM units across a facility, it changes the management model. One staff member can monitor heating status, check door sensors, and schedule sessions across every sauna without switching accounts or toggling between views.

HUUM has offered commercial-grade hardware since its UKU system first shipped. The multi-sauna dashboard now gives operators a software layer that matches.

The Full Feature List

Here is what HUUM is shipping in App 4.0, per the company’s own announcement to SaunaNews:

• 3x faster control: App and controller communicate three times faster, with instant response on every command
• All saunas in one view: Current and target temperature, status, and alerts for every connected sauna at a glance
• Smarter booking: Set day, time, temperature, and duration in seconds, with recurring sessions
• Advanced statistics: Total sauna hours, full session history, per-session heating charts
• Real-time alerts: Instant feedback on open doors, lost Wi-Fi connections, and remote-start safety checks
• Improved user management: Better handling of shared and commercial sauna environments
• Full dark theme: System-wide dark mode
• Accessibility improvements: Interface updates across the entire app

The UKU control system comes in three versions: UKU Local (wall panel only), UKU WiFi (app control via home network), and UKU 4G (app control via cellular for remote locations). App 4.0 works with both WiFi and 4G variants. The UKU system supports heaters up to 18 kW and is compatible with electric heaters from multiple manufacturers.

Where This Fits in the Smart Sauna Market

HUUM was the first sauna manufacturer to ship a smartphone-connected control system, back in 2014. That head start gave it a decade of installed base, but the original app accumulated years of technical debt.

The competitive context has shifted. Harvia phased out Xenio WiFi and moved remote start behind a paid upgrade in its Fenix line. Saunum has been iterating on its own app with the Leil software updates. Operators who need reliable app control for commercial environments now have fewer options than they did two years ago, and HUUM is betting that a ground-up rebuild positions it as the most capable remaining choice.

The rebuilt server infrastructure is the part competitors cannot easily replicate. A fresh UI can be designed in months. A rewritten backend that cuts latency by two-thirds requires rethinking the entire data pipeline between phone, cloud, and wall panel. HUUM’s own framing is telling: “We listened closely to your feedback, and then we went all in.”

The sign-off on the company’s announcement to SaunaNews: “Enjoy the leil.” If the server infrastructure performs as advertised, more owners will.