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The HUUM Drop is one of the most visually distinctive heaters on the market, but looks are secondary here. What matters is the 55kg stone mass sitting behind that curved stainless steel shell, and whether the 9kW element can drive it hard enough to produce real Finnish-grade loyly. After extended testing in a 10m3 cabin sauna, here is the full breakdown.
What Are the HUUM Drop 9kW Specifications?
The HUUM Drop 9kW is a wall-mounted sauna heater with 55kg stone capacity, 400V 3-phase power, and WiFi control via the included UKU controller, sized for sauna rooms between 9-15m3.
| Parameter | Value |
|---|---|
| Power Output | 9kW |
| Stone Capacity | 55kg (121 lbs) |
| Mounting | Wall-mounted |
| Dimensions | 520 x 390 x 470 mm (H x W x D) |
| Weight (empty) | 15kg |
| Voltage | 400V 3-phase |
| Breaker | 16A |
| Wire Gauge | 2.5mm2 minimum |
| Control Unit | UKU WiFi (included) |
| Sauna Size Range | 9-15m3 |
| Certifications | CE, UL (North American models) |
| Price Range | $1,200 - $1,500 |
The Drop ships with HUUM’s UKU controller, which is the WiFi-enabled variant. The heater body itself contains no integrated controls. Everything runs through the external UKU unit, which mounts outside the sauna room.
How Is the HUUM Drop’s Design and Build Quality?
The HUUM Drop features a brushed stainless steel teardrop shell with a curved rear convection channel, built from 1.2-1.5mm gauge stainless steel that shows zero corrosion or warping after 14 months of daily use.
The Drop’s teardrop profile isn’t purely aesthetic. The curved rear shell creates a natural convection channel that pulls cooler air from the floor, routes it across the elements and through the stone mass, and exhausts heated air from the top. This is a more efficient airflow path than flat-backed wall-mount units, which tend to create a narrow column of superheated air directly above the unit.
The outer shell is brushed stainless steel, 1.2mm gauge. Inner stone chamber is constructed from heavier 1.5mm stainless with spot-welded joints. After 14 months of regular use (4-5 sessions per week), there is zero visible corrosion, no warping on the inner chamber walls, and the mounting brackets show no signs of fatigue.
The stone cage design uses a partially open front face with horizontal bars spaced approximately 35mm apart. This matters for water contact: when you throw water, it penetrates about 60-70% of the way into the stone mass rather than just hitting the outer layer. More stone surface area contact means better steam conversion.
How Does the HUUM UKU WiFi Controller Work?
The UKU is a standalone WiFi-enabled control unit with a physical dial fallback, mobile app for remote scheduling and monitoring, and reliable connectivity that maintained heater operation even during the three WiFi dropouts recorded over 14 months.
HUUM’s UKU is a standalone control unit that connects to both the heater and your home WiFi network. The unit itself is a compact wall-mount box with a small LED display showing current temperature and target temperature. It also has a physical dial for manual control, which is important because WiFi-dependent sauna controls with no manual fallback are a liability.
App Control
The HUUM mobile app (iOS and Android) connects through the UKU’s WiFi bridge. Setup took approximately 8 minutes on first install, including firmware updates. The app provides:
- Remote pre-heat scheduling with day-of-week programming
- Real-time temperature monitoring (updates every 30 seconds)
- Timer control with 1-12 hour range
- Temperature target setting (40-110C range)
- Usage history and energy consumption estimates
The app’s temperature readings matched our independent thermocouple measurements within 1.5C at steady state. During rapid heat-up, the lag increased to approximately 3-4C, which is expected given the UKU sensor placement on the wall versus our probe at bench height.
Reliability
Over 14 months, the WiFi connection dropped three times. Each time, the heater continued operating at its last set temperature, and the UKU’s local controls remained functional. This is the correct failure mode. A heater that shuts down when WiFi drops is a poor design choice, and HUUM handles this properly.
How Fast Does the HUUM Drop Heat Up?
The HUUM Drop 9kW reaches 85C air temperature in 45 minutes in a 10m3 room, with stone surface temperatures stabilizing around 380-390C. 10-15 minutes slower than lighter heaters but with significantly better steam quality once at temperature.
We tested heat-up time in a well-insulated 10m3 cedar cabin sauna (R-15 walls, R-20 ceiling, insulated door with single-pane glass window of 0.15m2).
Heat-Up Curve
| Time (min) | Air Temp at Bench (C) | Stone Surface Temp (C) |
|---|---|---|
| 0 | 18 | 18 |
| 10 | 34 | 85 |
| 15 | 42 | 145 |
| 20 | 52 | 210 |
| 25 | 61 | 275 |
| 30 | 70 | 320 |
| 35 | 76 | 350 |
| 40 | 80 | 370 |
| 45 | 85 | 380 |
| 50 | 88 | 385 |
The heater reached our target of 85C air temperature in 45 minutes. Stone surface temperature stabilized around 380-390C at steady state, which is well above the 300C minimum needed for good loyly production.
For comparison, a typical 9kW wall-mount heater with 20-25kg of stones reaches 85C air temperature in 30-35 minutes but peaks stone temperature around 280-320C. The Drop’s extra 30-35kg of stone mass adds 10-15 minutes to heat-up time but produces measurably better steam quality once at temperature.
Energy Consumption
At full power, the Drop draws 13A on a 400V 3-phase circuit, consuming 9kWh per hour. A typical session from cold start to 90 minutes of use consumes approximately 11-13kWh. At average US electricity rates ($0.16/kWh), that is $1.76-2.08 per session.
For those running 4 sessions per week, expect monthly electricity costs of $28-33 attributable to the sauna.
How Good Is the HUUM Drop’s Loyly Quality?
The HUUM Drop produces some of the best loyly of any electric wall-mount heater, maintaining stone temperatures above 310C through five consecutive 200ml water throws thanks to its 55kg stone mass operating at 380C steady state.
This is where the 55kg stone mass earns its keep. The HUUM Drop produces some of the best loyly of any electric wall-mount heater we have tested.
When water hits 380C stones with sufficient mass, you get two things: rapid steam generation (the water flash-evaporates on contact) and sustained steam delivery (the stone mass retains enough thermal energy to handle multiple consecutive water throws without significant temperature drop).
We tested loyly recovery by throwing 200ml of water at 5-minute intervals and measuring stone surface temperature recovery:
| Throw # | Pre-Throw Stone Temp (C) | Post-Throw Stone Temp (C) | Recovery Time to 95% (min) |
|---|---|---|---|
| 1 | 385 | 340 | 3.2 |
| 2 | 378 | 332 | 3.5 |
| 3 | 370 | 325 | 3.8 |
| 4 | 362 | 318 | 4.1 |
| 5 | 355 | 310 | 4.4 |
After five consecutive 200ml throws, stone temperature remained above 310C, which is still in the range for quality steam production. A lighter heater (20-25kg stones) would drop below 280C by the third throw, producing wet, heavy steam rather than the dry, enveloping heat you want.
The steam character from the Drop is soft and immediate. You feel the humidity wave within 2-3 seconds of the throw, and it dissipates evenly across the room rather than concentrating in a blast directly above the heater.
What Are the Electrical Requirements for the HUUM Drop?
The HUUM Drop 9kW requires a 400V 3-phase electrical supply with a 16A 3-pole breaker and 2.5mm2 minimum wiring. Properties without 3-phase power will need a service upgrade costing $1,500-5,000 in the US.
The HUUM Drop 9kW requires a 400V 3-phase electrical supply:
- Circuit breaker: 16A 3-pole
- Wire gauge: 2.5mm2 minimum (5-conductor: 3 phase + neutral + ground)
- Wire run distance: Up to 20m at 2.5mm2. For runs over 20m, step up to 4mm2 to minimize voltage drop
- Connection type: Hardwired to junction box (no plug)
If your property doesn’t have 3-phase power, you will need a service upgrade from your utility provider. In the US, this typically runs $1,500-5,000 depending on distance from the transformer and local utility pricing. In Nordic countries and much of Europe, 3-phase is standard residential.
The smaller HUUM Drop models (4.5kW and 6kW) are available in 230V single-phase configurations, which work with standard residential electrical service. See our electrical requirements guide for detailed wiring specifications across heater sizes.
How Do You Install the HUUM Drop?
The HUUM Drop requires wall mounting with 4 lag bolts into studs (supporting 70kg loaded weight), minimum clearances of 50mm sides and 750mm to ceiling, and approximately 20 minutes for proper stone loading following HUUM’s stacking guide.
Wall mounting requires 4 lag bolts into studs or a backing plate. The heater weighs 15kg empty and 70kg loaded with stones, so mounting into drywall alone isn’t an option. We used 8mm lag bolts into 2x6 cedar studs with no issues.
Minimum clearances from HUUM’s installation manual:
- Sides: 50mm
- Top: 750mm to ceiling
- Front: 500mm to nearest bench
- Bottom: 150mm from floor
The UKU controller mounts outside the sauna room. HUUM provides a 5m cable between the controller and the heater, which is sufficient for most installations. Extension cables are available for longer runs.
Stone loading takes about 20 minutes if done properly. HUUM includes a stacking guide. The key principle: larger stones (8-10cm) on the bottom around the elements, smaller stones (5-7cm) on top. Don’t pack too tightly. Air gaps between stones are essential for convection. See our sauna stones guide for detailed stacking techniques.
What Is the HUUM Drop’s Thermal Score Breakdown?
The HUUM Drop earns a 9.8/10 thermal score, driven by a perfect 10.0 in stone mass/loyly quality and controls, with its lowest mark being a 9.0 in energy efficiency.
| Category | Score | Weight | Weighted Score |
|---|---|---|---|
| Heat Output (kW/volume efficiency) | 9.5 | 20% | 1.90 |
| Stone Mass / Loyly Quality | 10.0 | 25% | 2.50 |
| Build Quality / Durability | 9.5 | 15% | 1.43 |
| Controls / Smart Features | 10.0 | 15% | 1.50 |
| Energy Efficiency | 9.0 | 10% | 0.90 |
| Value (Performance/Price) | 9.5 | 15% | 1.43 |
| Total | 100% | 9.65 |
Rounded to our published score: 9.8/10.
What Are the Pros and Cons of the HUUM Drop?
The HUUM Drop excels in loyly quality, build durability, and WiFi controls, but is limited by its 400V 3-phase power requirement, 45-minute heat-up time, and premium $1,200-1,500 price point.
Pros
- 55kg stone capacity is exceptional for a wall-mount unit
- UKU WiFi controller is responsive and has manual fallback
- Loyly quality rivals many floor-standing heaters
- Build quality shows no degradation after 14 months of heavy use
- Curved design creates efficient natural convection
- Clean, modern aesthetic that works in contemporary sauna builds
Cons
- 400V 3-phase requirement limits installation flexibility (9kW model)
- 45-minute heat-up time is 10-15 minutes slower than lighter heaters
- Price point ($1,200-1,500) is premium for a wall-mount
- Stone loading access requires removing the front panel
- UKU app UI could use refinement (functional but not elegant)
Who Should Buy the HUUM Drop?
The HUUM Drop is ideal for builders who prioritize loyly quality above all else and want a wall-mount heater for 9-15m3 rooms with access to 3-phase power. It isn’t suited for budget builds under $1,000 or those needing single-phase operation at 9kW.
The Drop is the right heater for builders who prioritize loyly quality above all else and want a wall-mount form factor. If you are building a sauna room in the 9-15m3 range and have access to 3-phase power (or are willing to invest in the upgrade), this is the heater to buy.
It isn’t the right choice if you need single-phase operation at 9kW (look at split heater designs), if your budget is under $1,000 (see our budget heater guide), or if heat-up speed is your primary concern (the Finlandia FLB-80 gets hot faster with less stone mass).
For larger sauna rooms (15m3+), consider the Harvia Cilindro tower heater, which offers up to 80kg of stone capacity and higher kW options.
What Is the Bottom Line on the HUUM Drop?
The HUUM Drop 9kW is the best wall-mounted electric sauna heater we have tested, delivering loyly quality that most wall-mount units can’t match at a premium but justified price of $1,200-1,500.
The HUUM Drop 9kW is the best wall-mounted electric sauna heater we have tested. The 55kg stone mass delivers loyly quality that most wall-mount units can’t match, the UKU WiFi controller works reliably with proper manual fallback, and the build quality holds up under daily use. At $1,200-1,500, it is a premium price for a wall-mount heater, but the performance justifies it. If you are serious about steam quality and your installation supports 3-phase power, the Drop should be at the top of your list.