HUUM Core Now in the US: The Only Electric Heater That Disappears Into Your Bench
The Estonian-made HUUM Core can be clad in the same wood as your sauna walls and benches, making it the first electric heater designed to visually vanish into the room.
The HUUM Core in use: the stone basket sits flush at bench height, allowing bathers to ladle water without reaching to the floor.
HUUM, the Estonian heater maker known for its sculptural DROP and HIVE designs, has brought its Core series to the US market. Its central design idea is one no American-made electric heater has matched: the unit accepts factory-engineered wood panels in alder, aspen, or thermo-aspen, the same species used to build most North American sauna interiors. Clad correctly, the heater disappears into the bench.
That is not a small thing if you care about how a sauna looks. Most residential electric heaters are industrial objects surrounded by a wood guard rail. The Core is designed to sit inside the bench structure itself, with only the stone basket visible above the bench surface. The effect is something closer to what you see in high-end spa installations, without the custom metalwork bill.
What Makes It Different
The Core is bench-embeddable by design. Its double-wall chassis requires only 2 inches of clearance from combustible materials, a fraction of what most competitors need. That tight clearance makes it physically possible to frame the heater into a bench structure and surround it with matching wood. Air must remain unobstructed at the base to keep the convection cycle running, but the sides and visible surfaces can be finished to match the room exactly.
HUUM sells three factory-engineered wood panel kits for the Core. Alder offers a warm reddish-brown tone and strong dimensional stability. Aspen runs light and knot-free, staying cool enough to the touch to reduce burn risk. Thermo-aspen has been heat-treated to a rich chocolate color and resists moisture better than untreated wood, making it a longer-lasting choice in high-humidity conditions. All three species are standard in North American sauna interiors. If your benches are thermo-aspen, your heater can be thermo-aspen.
The alternative option is the Core ST (also called the Naked variant), which ships without exterior panels entirely. Builders can attach custom cladding in natural stone, ceramic tile, tempered glass, or their own woodwork. Side panels are limited to 44 lbs each and attached with included M5x8 screws. For projects with bespoke architectural requirements, this is the version to specify.
The ready-to-install option is the Core Black, which has a matte black metal exterior with matching black inlays. No carpentry required, ships and installs as a finished unit.
Certified to 230°F
The Core carries an SGS certification rather than a standard UL listing. SGS is an OSHA-recognized Nationally Recognized Testing Laboratory, and its certifications are accepted by US building inspectors. The difference matters here: standard UL-listed electric sauna heaters in the US are capped at 194°F (90°C). The Core's SGS certification allows it to reach 230°F (110°C).
That 36-degree gap is meaningful in practice. Traditional Finnish sauna protocols frequently require temperatures above 200°F to produce the cardiovascular and heat-shock protein responses associated with regular bathing. The Core is tested against UL 60335-1, CAN/CSA-C22.2 NO. 60335-1, and IEC 60335-2-53. The certification is legitimate and code-compliant; the higher ceiling just reflects European test standards rather than domestic ones.
For outdoor saunas, saunas with substantial glass walls, or rooms that struggle to hold heat, the additional thermal headroom is a practical advantage, not a spec sheet number.
Specs and Sizing
The Core ships in three power ratings: 6.5 kW (CORE 6), 9.0 kW (CORE 9), and 10.5 kW (CORE 11). All three share the same exterior dimensions: 32.7 inches tall, 15.2 inches square. That consistent footprint means framing and bench cutouts can be standardized regardless of which kilowatt version a given room requires. The heater weighs 41.9 lbs before stones.
Stone capacity is 66 lbs (30 kg) of olivine diabase, loaded in rounded 2-to-4-inch pieces. The stone mass is substantial enough to support repeated water applications without the temperature dropping sharply between rounds. Löyly quality is the right word for it: the steam produced by a well-loaded stone basket at operating temperature is soft rather than harsh, and the Core's stone-forward design prioritizes that over raw air temperature.
Electrical requirements follow standard US residential specs. The 6.5 kW model draws 25 amps and requires a 30-amp breaker on 10 AWG wire. The 9.0 and 10.5 kW models draw 37.5 to 43.75 amps and require a 50-amp breaker on 8 AWG wire. The unit is also compatible with 208V commercial power grids, though the output derate reduces effective kilowatt delivery proportionally.
The UKU Controller
The Core does not operate standalone. It requires a UKU control unit, which must be purchased alongside the heater. The UKU contains the logic board, contactors, and safety sensors. It mounts outside the sauna room and connects to a door sensor that cuts power if the door is left open.
The Wi-Fi version of the UKU connects the heater to the HUUM mobile app (iOS and Android), allowing remote activation and temperature monitoring from anywhere with a data connection. Because the Core's 66-pound stone mass takes 45 to 60 minutes to reach optimal temperature, remote start is genuinely useful rather than a gimmick. Set the heater from the office, walk in the door when it's ready.
The UKU controller console supports temperatures between 104°F and 230°F, allows delayed start up to 48 hours in advance, and is available in multiple finishes including black, glass, mirror, gold, and wood housings.
Where to Buy
The Core is available now through Sauna Marketplace in all three power ratings and panel finish options. The unit ships freight on a pallet to the contiguous 48 states. Orders can be canceled at no charge before the shipment leaves the warehouse, which matters for builders coordinating around permit timelines. Warranty coverage is three years for residential use, one year for commercial. Heating elements are excluded from warranty across all variants, which is standard in the industry. Free one-on-one video and phone consultations are available for buyers working through the sizing and electrical requirements.
Wood-clad sauna heaters exist in the European market. In the US, they have been a custom fabrication problem: expensive to execute and dependent on finding a builder who knows how to frame a heater safely into a bench. The Core makes this a product decision rather than a construction problem. For anyone building a sauna where the aesthetic matters as much as the performance, that changes the calculus significantly.
Sofia Mäkelä
Industry Reporter, SaunaNews
Sofia Mäkelä is an industry reporter based in Helsinki with deep ties to the Nordic sauna manufacturing community. A graduate of Aalto University, she spent five years covering industrial technology for Kauppalehti before turning her focus to the sauna sector full-time. Her reporting on supply-chain dynamics and manufacturer strategy has broken several major stories in the trade press.
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