HUUM STEEL Mini 4 STEEL Mini Series 3.5kW Sauna Heater
The HUUM STEEL Mini 4 is a 3.5kW wall-mounted electric sauna heater for small sauna rooms from 106 to 177 adjusted cubic feet - HUUM's most compact and narrowest electric floor model, and the entry point of the STEEL Series lineup. The STEEL Mini mounts on the sauna wall and anchors at the floor for stability, with a profile of just 12.6"W x 6"D x 38.4"H - only half the depth of the full STEEL 6's 12.6"D body. Despite this ultra-slim depth of 6", the STEEL Mini holds 132 lbs of sauna stones (4 boxes, 3-5 cm rounded olivine, sold separately) in an open-air design that showcases all the stones and keeps the heating elements in direct contact with the stone mass. HUUM's description of the visual and experiential quality is direct: an open-air design showcases all 132 lbs of stone, bringing an ambience of natural charm while encouraging water-pouring for powerful, soft steam. Safety distances from walls are just 2.5" (6.4 cm) on the sides. An internal air tunnel increases heating speed by up to 25% and extends element life. The UKU Local or UKU Wi-Fi controller is required and sold separately. No UKU Extension Box is needed for the 3.5kW model. 240V/1PH, 15A circuit breaker, 14AWG. Max temperature 230°F. SGS certified. 5-year limited warranty (excluding elements). Designed and made in Estonia by HUUM.
STEEL Mini - the narrowest HUUM electric heater, wall-mounted for small saunas
The STEEL Mini is described by HUUM directly as an even slimmer 3.5kW wall-mounted model which is particularly suitable for very small sauna rooms. At 6" depth, it is half as deep as the STEEL 6 (12.6"D) and designed specifically for sauna rooms and installation layouts where even the full STEEL's compact profile would be too much. The wall-mounting bracket included with the STEEL Mini anchors the heater to the wall; a floor anchor provides additional stability. For a small apartment sauna, a compact personal sauna, or any room in the 106-177 cu ft range where the wall must carry the heater rather than the floor, the STEEL Mini is the purpose-built specification in the HUUM electric lineup. The open-air stone design - with the full 132-lb stone column exposed - gives the STEEL Mini a visual presence larger than its 6" depth suggests.
Open-air stones, direct element contact, and an air tunnel
Unlike the STEEL 6's enclosed stone cavity, the STEEL Mini features an open-air design where the stone mass is fully visible and exposed from the front. HUUM and multiple authorized dealers describe this as one of the STEEL Mini's distinctive qualities: more exposed stones create a longer and milder heat, with better steam capability. The heating elements are in direct contact with the stones, maximising heat transfer from element surface to stone mass. The internal air tunnel system channels air through the stone column to distribute heat efficiently and increase heating speed by up to 25%. HUUM notes that the air tunnel also extends the life of the heating elements by preventing localized overheating at element surfaces. At 3.5kW on 240V/1PH, 15A circuit, and 14AWG wire, the STEEL Mini is also the most electrically straightforward HUUM heater - requiring less electrical capacity than any other model in the lineup.
132 lbs of stones in a 6"-deep wall mount - proportionally exceptional capacity
HUUM states plainly that the STEEL Mini has an exceptionally large rock capacity compared with other heaters in this power range, resulting in more consistent heat, more steam capability, and a superior bathing experience. At 132 lbs of rounded olivine stones (4 boxes, 3-5 cm) in a 3.5kW heater, the stone-to-power ratio is deliberately high: the large stone mass accumulates heat gradually and releases it consistently throughout the session, producing long-lasting, mild steam rather than the sharp, brief steam of a low-stone-mass heater cycling on and off rapidly. For a small personal sauna where soft, sustained heat quality is a priority over raw output, the STEEL Mini's stone capacity makes it an elevated choice for its power class.
3.5kW wall-mounted electric sauna heater for rooms from 106 to 177 adjusted cubic feet. STEEL Mini Series - HUUM's narrowest electric model. Ultra-slim 12.6"W x 6"D x 38.4"H wall-mount profile. Open-air stone design - 132 lbs stones fully visible. Direct element-to-stone contact. Internal air tunnel - heats up to 25% faster - extends element life. Safety distances: 2.5" (6.4 cm) sides. 132 lbs stones required (4 boxes, 3-5 cm rounded olivine, sold separately). UKU Local or UKU Wi-Fi controller required - sold separately. No UKU Extension Box required. Max temperature 230°F. 240V/1PH - 15A circuit breaker - 14AWG. Dimensions: 12.6"W x 6"D x 38.4"H. Pallet delivery required. SGS certified. 5-year limited warranty (excluding elements). Designed and made in Estonia by HUUM.
3.5 kW 106 to 177 cu ft (adjusted) STEEL Mini Series - HUUM's narrowest electric model Wall-mounted - floor-anchored Ultra-slim 6"D profile Open-air stone design - 132 lbs fully visible Direct element-to-stone contact Internal air tunnel - 25% faster heat-up Safety distances: 2.5" sides 132 lbs stones required (4 boxes, 3-5 cm rounded olivine) UKU controller required - sold separately No UKU Extension Box required Max temperature 230°F 240V/1PH - 15A - 14AWG 12.6"W x 6"D x 38.4"H SGS certified 5-year limited warranty (excl. elements) Designed and made in Estonia by HUUM
⚠️ 132 lbs sauna stones (4 boxes, 3-5 cm rounded olivine) required - not included. UKU controller required - not included. Both stones and controller must be purchased separately before the heater can be operated. Stones are 3-5 cm rounded olivine - do not substitute with larger stones or decorative stones which can break under heat. An additional box of stones is recommended. No UKU Extension Box is required for the 3.5kW model. A licensed electrician is required for all wiring: 240V/1PH, 15A circuit breaker, 14AWG wire. This heater ships by scheduled pallet freight - a delivery appointment is required. Room size uses adjusted cubic feet - cold surfaces (glass, tile, natural rock) require additional adjustment. Confirm adjusted room size before purchase.
ℹ️ HUUM STEEL Mini 4 vs HUUM STEEL 6 - wall-mount Mini vs floor-standing full STEEL, same Series. HUUM STEEL Mini 4 H1007012 (this listing): 3.5kW, 106-177 cu ft (adjusted), wall-mounted, 12.6"W x 6"D x 38.4"H (only 6" deep), 132 lbs stones (4 boxes), open-air stone design fully visible, 2.5" side clearances, 15A/14AWG. HUUM's most compact and narrowest electric model. Right for very small sauna rooms where wall mounting and a 3.5kW output are the correct specification. HUUM STEEL 6 H1006012: 6kW, 212-353 cu ft, floor-standing, 12.6"W x 12.6"D x 38.4"H (12.6" deep), 330 lbs stones (10 boxes), 2" side clearances, 30A/10AWG. Right for larger small saunas where floor standing and 6kW output are needed. Both share the same STEEL Series design philosophy, stainless steel construction, internal air tunnel, UKU controller compatibility, and 5-year warranty. Choose the STEEL Mini 4 for the 106-177 cu ft range with wall mounting. Choose the STEEL 6 for the 212-353 cu ft range with floor standing.
Specifications
Performance
| Power output |
3.5 kW |
| Fuel type |
Electric (240V/1PH) |
| Room volume |
106 to 177 cu ft (adjusted) |
| Max temperature |
230°F (110°C) |
| Stone capacity |
132 lbs / 60 kg (4 boxes, 3-5 cm rounded olivine) - sold separately |
| Stone size |
3-5 cm rounded olivine (1-2 in) |
| Air tunnel benefit |
Heats up to 25% faster - extends element life |
| Stone design |
Open-air - stones fully visible - direct element contact |
Safety distances
| Sides (A) |
2.5 in (6.4 cm) |
| Front (B) |
15.5 in (393 mm) |
| STEEL Mini vs STEEL 6 sides |
STEEL Mini: 2.5 in | STEEL 6: 2.0 in |
Electrical
| Voltage / phase |
240VAC, 1-phase, 60Hz |
| Circuit breaker |
15A |
| Wire size |
14AWG |
| UKU Extension Box |
Not required (only needed for 10.5kW+ models) |
| Certification |
SGS certified |
Controller (required - sold separately)
| Compatible controllers |
UKU Local | UKU Wi-Fi | UKU Glass | UKU Mirror | UKU Gold |
| UKU Local |
Physical panel - temperature, timer, safety features |
| UKU Wi-Fi |
Physical panel + HUUM mobile app remote control |
| UKU safety features |
Door sensor, overheating protection, child safety lock |
Physical dimensions
| Width |
12.6 in (320 mm) |
| Depth |
6 in (152 mm) |
| Height |
38.4 in (975 mm) |
| Installation |
Wall-mounted + floor-anchored for stability |
| Delivery |
Scheduled pallet freight - appointment required |
STEEL Mini vs STEEL 6 - dimension comparison
| Width (both) |
12.6 in (320 mm) - identical |
| Height (both) |
38.4 in (975 mm) - identical |
| Depth - STEEL Mini |
6 in (152 mm) |
| Depth - STEEL 6 |
12.6 in (320 mm) |
| Stone capacity - STEEL Mini |
132 lbs (4 boxes) |
| Stone capacity - STEEL 6 |
330 lbs (10 boxes) |
| Circuit breaker |
STEEL Mini: 15A / STEEL 6: 30A |
| Wire |
STEEL Mini: 14AWG / STEEL 6: 10AWG |
Construction
| Body material |
Stainless steel |
| Elements |
Industrial-grade stainless steel |
| Stone design |
Open-air - stones visible and exposed |
| Element-stone contact |
Direct - maximum heat transfer efficiency |
| Internal air tunnel |
Yes - 25% faster heat-up, extends element life |
| Origin |
Designed and made in Estonia by HUUM |
| Warranty |
5-year limited (excluding elements) |
Optional accessories (sold separately)
| Safety railing |
HUUM STEEL safety railing (light wood profiles) |
| Embedding flanges |
Available for bench integration |
| Reflector panel |
HUUM Reflect S (can reduce safety distances further) |
What's included
HUUM STEEL Mini 4 3.5kW wall-mounted electric sauna heater with internal air tunnel
Wall mounting bracket
Installation and operation manual
5-year limited warranty (excluding elements)
Required (not included): 132 lbs sauna stones (4 boxes, 3-5 cm rounded olivine - an additional box is recommended); HUUM UKU controller (Local or Wi-Fi). No UKU Extension Box is required for the 3.5kW model. Optional accessories (sold separately): HUUM STEEL safety railing; embedding flanges; HUUM Reflect S reflector panel. A licensed electrician is required for all wiring: 240V/1PH, 15A circuit breaker, 14AWG wire.
Why the HUUM STEEL Mini 4 stands out
Only 6" deep - HUUM's narrowest electric model
At 6" (152mm) depth, the STEEL Mini is the narrowest electric sauna heater HUUM produces - half the depth of the full STEEL 6 and significantly shallower than any other HUUM electric floor model. HUUM describes it as an even slimmer 3.5kW wall-mounted model particularly suitable for very small sauna rooms. For a compact apartment sauna, a personal barrel sauna, or a custom sauna built into a tight space, the STEEL Mini's 6" depth means it occupies significantly less wall-to-bench clearance than any HUUM alternative. The 12.6" width is identical to the full STEEL 6 - the significant dimension reduction is entirely in the depth.
Open-air stone design - 132 lbs fully visible
The STEEL Mini's open-air stone design is visually and experientially distinct from heaters with enclosed stone cavities. All 132 lbs of rounded olivine stones are visible from inside the sauna - the full stone column is exposed and the warm, natural texture of the stones becomes part of the sauna's visual character. HUUM's description of the experience: an open-air design showcases all 132 lbs of stone, bringing an ambience of natural charm while encouraging water-pouring for powerful, soft steam. The exposed stones also allow direct contact between the heating elements and the stone mass, maximising heat transfer efficiency from element to stone.
132 lbs of stones at 3.5kW - exceptionally high ratio
At 132 lbs of stones in a 3.5kW heater, the STEEL Mini has an exceptionally high stone-to-power ratio. HUUM states this directly: the STEEL Mini has an exceptionally large rock capacity compared with other heaters in this power range, resulting in more consistent heat, more steam capability, and a superior bathing experience. The large stone mass relative to the power input means the stones take longer to reach full temperature, but once charged they hold heat and produce consistent steam through the full session with minimal cycling. For a small personal sauna where long-lasting soft steam quality matters more than fast heat-up time, this ratio is exactly the right design trade-off.
Internal air tunnel - 25% faster heat-up, longer element life
The internal air tunnel channels air through the stone mass in a controlled pattern, distributing heat evenly through the full 132-lb stone column and increasing heating speed by up to 25%. The air tunnel also reduces thermal stress on the heating elements by preventing localised heat concentration at element surfaces - HUUM notes that the air tunnel extends element life as a direct benefit. For a 3.5kW heater heating a 106-177 cu ft sauna room, the 25% faster heat-up translates to a meaningfully shorter wait from switch-on to bathing temperature. The air tunnel is the same design principle used in the full STEEL 6, scaled to the Mini's narrower body.
15A / 14AWG - the lightest electrical requirement in the HUUM lineup
The STEEL Mini 4 requires just a 15A circuit breaker and 14AWG wire - the smallest electrical capacity of any HUUM heater. This is practically significant for installations in older homes, apartments, or sauna buildings where additional electrical capacity is limited. Many apartment sauna installations and small home saunas already have a 15A 240V circuit available. No UKU Extension Box is required for the 3.5kW model - only the heater and a UKU controller (Local or Wi-Fi) are needed for a complete operating system. The STEEL Mini is the most electrically accessible HUUM electric heater in the lineup.
STEEL Series - Mini 4, STEEL 6, STEEL 9, STEEL 10.5
The H1007012 is the 3.5kW wall-mounted entry point of the HUUM STEEL Series. The STEEL Series also includes floor-standing models: STEEL 6 (6kW, 212-353 cu ft, 12.6"D, 330 lbs stones / 10 boxes, 30A/10AWG, 2" clearances), STEEL 9 (9kW, 4" clearances), and STEEL 10.5 (10.5kW, requires UKU Extension Box). The STEEL Mini 4 at 3.5kW serves the smallest sauna rooms (106-177 cu ft) where wall mounting, a 6"-depth profile, and a 15A electrical footprint are the specification. All STEEL models share the HUUM STEEL design aesthetic, internal air tunnel, direct element-to-stone contact, rounded olivine stone specification (3-5 cm), SGS certification, and 5-year limited warranty. Designed and made in Estonia by HUUM. We are an authorized HUUM dealer.
About HUUM
Designed in Estonia - SGS Certified - STEEL Mini Series - Wall-Mounted
HUUM STEEL Mini 4. 3.5kW. 106-177 cu ft. 6" deep. 132 lbs stones. Open-air design. Wall-mounted.
HUUM is an Estonian sauna heater company. The STEEL Mini 4 is HUUM's narrowest electric model - a 3.5kW wall-mounted heater for the smallest home saunas, just 6" deep with an open-air stone design that showcases all 132 lbs of rounded olivine stones. Internal air tunnel for 25% faster heat-up. 2.5" side clearances. UKU controller and 132 lbs stones (4 boxes, 3-5 cm) required and sold separately. No UKU Extension Box required. 15A/14AWG. Pallet delivery. We are an authorized HUUM dealer.
-
3.5kW electric - 106-177 cu ft (adjusted) - STEEL Mini wall-mounted
-
Ultra-slim 6"D profile - HUUM's narrowest electric model
-
Open-air stone design - 132 lbs fully visible - direct element contact
-
Internal air tunnel - 25% faster heat-up - 2.5" side clearances
- UKU controller required (no Extension Box) - 15A - 14AWG - SGS certified
STEEL Mini 4 vs STEEL 6 vs HIVE 12 - HUUM electric heater sizing guide
STEEL Mini 4 vs STEEL 6 vs HIVE 12 Electric - selecting the right HUUM electric heater
Three HUUM electric heaters span the full range from smallest to largest home sauna room. HUUM STEEL Mini 4 H1007012 (this listing): 3.5kW, 106-177 cu ft (adjusted), wall-mounted, 12.6"W x 6"D, 132 lbs stones (4 boxes, 3-5 cm), 2.5" side clearances, 15A/14AWG, open-air stone design. Right for the smallest sauna rooms where wall mounting, a 6"-depth profile, and minimum electrical footprint are the specification. HUUM STEEL 6 H1006012: 6kW, 212-353 cu ft, floor-standing, 12.6"W x 12.6"D, 330 lbs stones (10 boxes, 3-5 cm), 2" side clearances, 30A/10AWG. Right for small to medium home saunas where floor standing and 6kW are needed. HUUM HIVE 12 Electric H1003012: 12kW, 424-636 cu ft, cylindrical open beehive design, very large stone capacity (approx. 550 lbs), dual 30A breakers, UKU Extension Box required. Right for larger rooms where the HIVE's distinctive cylindrical design and high output are the specification. All three carry HUUM's 5-year warranty and require a UKU controller sold separately. Choose the STEEL Mini 4 for rooms from 106 to 177 adjusted cubic feet where wall mounting, minimal depth, and light electrical requirements are the priorities.
Manuals and Documents
Warranty
5-year limited warranty (excluding elements)
The HUUM STEEL Mini 4 carries HUUM's 5-year limited warranty from the date of purchase. The warranty covers defects in manufacturing and materials under normal use and maintenance conditions. Heating elements are excluded from the 5-year term and carry a separate warranty period per the warranty document. The warranty does not cover damage caused by improper installation, failure to follow the installation and operating guidelines, use of incorrect stone type or size (decorative stones must not be used as they can break under heat; use only rounded olivine 3-5 cm), operating without the required stone load, or damage from inadequate electrical installation. HUUM recommends using rounded olivine sauna stones for milder steam and to complement the open-air design of the STEEL Mini. Proof of purchase from an authorized HUUM dealer is required for warranty claims. We are an authorized HUUM dealer.
