The HUUM HIVE Flow LS is a 9.8kW wood-burning sauna stove for rooms from 282 to 635 cubic feet with a firebox extension that passes through the sauna wall for loading from an adjacent room or outdoors. LS identifies the through-wall firebox configuration: the stove body and 330-lb stone cage sit inside the sauna, the firebox bushing extends through the wall, and the glass door faces the adjacent room. Bathers inside the sauna are completely undisturbed throughout the session. The HIVE Flow LS is the larger configuration of the HUUM Flow platform - 9.8kW vs the HIVE Flow Mini's 8.5kW, 330 lbs of stones vs 231 lbs, and a larger room range of 282-635 cu ft vs 212-494 cu ft. Both share the same patent-pending furnace design that retains 75% of firewood heat inside the sauna, produces CO emissions of just 346 mg/m3 (vs 1,000+ in comparable stoves), achieves particulate matter output of 25 mg/m3 - the lowest in its category - and achieves safety distances of just 150mm (5.9") at the sides and back from combustible materials. The HIVE Flow LS weighs 161 lbs (73 kg). Top or back 115mm chimney connection. Max firewood 11.8" (300mm). BImSchV and CPR certified. 5-year limited warranty (excluding elements). Designed, engineered, and made in Estonia by HUUM.
LS firebox extension - load from outside, sauna session undisturbed
The LS configuration of the HIVE Flow adds a firebox bushing that passes through the sauna wall into an adjacent room or outdoors. Wood is loaded, the fire is managed, and the glass door allows the person in the adjacent space to watch the flames - all from outside the sauna. Bathers inside receive 9.8kW of heat and the steam from 330 lbs of stones without the sauna door opening for firewood at any point in the session. HUUM's own description of the LS model is direct: it allows you to heat the sauna from an adjacent room. The large glass furnace door enhances the cozy ambiance of the adjacent space, letting you enjoy the mesmerizing flames while the sauna warms. For a cabin sauna with a lounge, a sauna building where the fire is managed from outdoors, or any layout where exterior wood loading is operationally preferred, the HIVE Flow LS is the purpose-built configuration.
Flow furnace - 75% heat retention, lowest emissions in its category
The HIVE Flow LS shares the same patent-pending furnace design as the HIVE Flow Mini. Air flows inside the heater in a unique pattern that keeps 75% of the heat generated from burning wood inside the sauna rather than escaping through the chimney. HUUM's own summary of the practical effect: you can enjoy four sessions with the same amount of wood that would typically provide three sauna sessions. CO emissions of 346 mg/m3 compare to over 1,000 mg/m3 in comparable stoves. Particulate matter output of 25 mg/m3 is the lowest in its output category. BImSchV certification (the German clean combustion standard) and CPR certification confirm these are independently verified values, not manufacturer claims. The same Flow furnace design also produces the 150mm (5.9") safety distances at the sides and back - the heater warms up more evenly across the stove body, allowing snug installation that conventional stoves cannot achieve.
330 lbs of stones - up to 408 lbs with optional stone cage
The HIVE Flow LS holds 330 lbs (150 kg) of sauna stones in its primary stone compartment, and an optional HUUM stone cage accessory (sold separately) adds capacity for a further 77-88 lbs (35-40 kg) of stones for a total of up to 418 lbs (190 kg). HUUM's description of this configuration is straightforward: the large stone volume allows full sauna bathing even over 30 minutes after the fire has died. The 330-lb primary stone load charges thoroughly during the fire - at 9.8kW, the HIVE Flow LS heats faster than the Mini while holding more thermal mass - and the charged stones sustain heat and steam long after the fire burns down. Rounded sauna stones 5-10 cm in diameter are recommended by HUUM for milder steam and better air circulation through the stone mass. Max firewood length is 11.8" (300mm).
9.8kW wood-burning sauna stove with firebox extension for rooms from 282 to 635 cubic feet. HIVE Flow LS - firebox extends through sauna wall, wood loaded from adjacent room or outdoors. Glass door faces adjacent room. Bathers inside sauna undisturbed. Patent-pending Flow furnace: 75% heat retention - 4 sessions from 3 loads of wood. CO: 346 mg/m3 (vs 1,000+ in comparable stoves). PM: 25 mg/m3 - lowest in category. Safety distances: 150mm (5.9") sides and back - 500mm (19.7") front from combustible materials. No protective sheath required. 330 lbs stones required (10 boxes, sold separately). Up to 408 lbs with optional stone cage. Steam lasts over 30 min after fire is out. 5mm top / 3mm sides stainless steel. Large glass door. Top or back flue - 115mm. Max firewood 11.8" (300mm). 6" adapter required for North America (sold separately). Dimensions: 20.7"W x 29.5"D x 34.8"H. 161 lbs. BImSchV certified - CPR certified. Pallet delivery required. 5-year limited warranty (excl. elements). Designed and made in Estonia by HUUM.
9.8 kW 282 to 635 cu ft HIVE Flow LS - firebox extension through sauna wall Wood loaded from adjacent room or outdoors Glass door faces adjacent room 75% heat retention - 4 sessions per 3 wood loads CO: 346 mg/m3 - PM: 25 mg/m3 Safety: 150mm sides and back - no protective sheath 330 lbs stones required (10 boxes) Up to 408 lbs with optional stone cage Steam lasts over 30 min after fire out 5mm top / 3mm sides stainless steel Large glass door Top or back flue - 115mm - 6" adapter required Max firewood 11.8" (300mm) 20.7"W x 29.5"D x 34.8"H - 161 lbs BImSchV certified - CPR certified Pallet delivery required 5-year limited warranty (excl. elements) Designed and made in Estonia by HUUM
Specifications
Performance
| Power output |
9.8 kW |
| Fuel type |
Wood - no electricity required |
| Room volume |
282 to 635 cu ft (8-18 m3) |
| Stone capacity (primary) |
330 lbs / 150 kg (10 boxes) - sold separately |
| Stone capacity with cage |
Up to 408 lbs / 185 kg (optional stone cage) |
| Max firewood length |
11.8 in (300 mm) |
| Steam after fire out |
Over 30 minutes |
LS firebox extension
| Firebox access |
From outside the sauna room via wall bushing extension |
| Glass door faces |
Adjacent room - fire view from outside sauna |
| Wall requirement |
Non-combustible wall required for bushing |
| Dual-room effect |
Sauna heat inside + fire view and warmth outside |
Flow furnace efficiency and emissions
| Heat retention in sauna |
75% of firewood heat stays in sauna |
| Sessions per wood load |
4 sessions vs 3 for conventional stoves |
| CO emissions |
346 mg/m3 (vs 1,000+ mg/m3 in comparable stoves) |
| Particulate matter |
25 mg/m3 - lowest in its category |
| Certifications |
BImSchV (German clean combustion) | CPR certified |
Safety distances (combustible materials)
| Sides and back |
5.9 in (150 mm) |
| Front |
19.7 in (500 mm) |
| Vs conventional stoves |
Conventional: 200-500 mm | HIVE Flow: 150 mm sides/back |
| Protective sheath required |
No |
Physical dimensions
| Width |
20.7 in (530 mm) |
| Depth (with LS extension) |
29.5 in (750 mm) |
| Height |
34.8 in (884 mm) |
| Weight (LS model) |
161 lbs (73 kg) |
| Standard Flow weight (no LS) |
148 lbs (67 kg) |
HIVE Flow LS vs HIVE Flow Mini LS comparison
| Output |
Flow LS: 9.8kW | Flow Mini LS: 8.5kW |
| Room range |
Flow LS: 282-635 cu ft | Flow Mini LS: 212-494 cu ft |
| Stone capacity |
Flow LS: 330 lbs (10 boxes) | Flow Mini LS: 231 lbs (7 boxes) |
| Width |
Flow LS: 20.7 in | Flow Mini LS: 17.7 in |
| Flow furnace, emissions, clearances |
Identical - same patent-pending furnace design |
| Certifications, warranty |
Identical - BImSchV, CPR, 5-year |
Construction
| Top panels |
5 mm thick stainless steel |
| Sides |
3 mm thick stainless steel |
| Glass door |
Large - faces adjacent room in LS configuration |
| Ash management |
Ash drawer included |
| Cleaning access |
2 cleaning hatches included |
| Installation |
Floor-mounted, vertical orientation |
Flue, certifications, and optional accessories
| Flue connection diameter |
115mm (4.5") |
| Flue connection position |
Top or back - selected during installation |
| North American adapter |
6" (155mm) adapter required - sold separately |
| Origin |
Designed, engineered, and made in Estonia by HUUM |
| Warranty |
5-year limited warranty (excluding elements) |
| Optional cage |
HUUM stone cage - adds 77-88 lbs stones capacity |
| Optional protective cage |
HUUM Cage HSTV |
| Chimney kits |
HUUM Thru-Ceiling / Thru-Wall / Barrel Chimney Kit |
| Floor protection |
HUUM Protective Plate | HUUM Protective Bed LS |
What's included
HUUM HIVE Flow LS 9.8kW wood-burning sauna stove with LS firebox extension
Metal grate
Heat resistant glove
Splints
Metal fixing plates (x2)
Ash grate
Cleaning hatches (x2)
Ash drawer
Installation and operation manual
5-year limited warranty (excluding elements)
Required (not included): 330 lbs sauna stones (10 boxes, rounded 5-10 cm diameter recommended); 6" North American flue adapter; chimney connection. Optional accessories (sold separately): HUUM stone cage (adds 77-88 lbs additional stone capacity); HUUM Cage HSTV; HUUM Thru-Ceiling, Thru-Wall, or Barrel Chimney Kit; HUUM Protective Plate or Protective Bed LS; HUUM Mounting Collar. A licensed chimney professional is recommended for all flue installations. Non-combustible wall required for LS firebox bushing.
Why the HUUM HIVE Flow LS stands out
LS exterior loading - session undisturbed, fire managed outside
The LS firebox extension allows the HIVE Flow's fire to be tended entirely from outside the sauna room. The sauna door stays closed. Heat is not lost to wood loading. Bathers in the sauna are completely undisturbed. The glass door faces the adjacent room, providing the person managing the fire with a direct view of the flames and the ambient warmth of the fire's radiant heat from the firebox face. HUUM notes directly: the LS model allows you to heat the sauna from an adjacent room. For a cabin sauna with a lounge, a sauna building where the stove fire is managed from outdoors, or any layout where exterior loading is operationally preferred, the HIVE Flow LS is the exact configuration.
75% heat retention - 4 sessions per 3 wood loads
The patent-pending Flow furnace keeps 75% of the heat generated from burning wood inside the sauna. HUUM's precise statement of the practical consequence: you can enjoy four sessions with the same amount of wood that would typically provide three sauna sessions. For a sauna that fires regularly across a season of use, this 33% fuel saving adds up meaningfully in wood consumption, cost, and the effort of sourcing and storing firewood. The same Flow furnace design also produces dramatically lower emissions - CO at 346 mg/m3, particulates at 25 mg/m3 - as a direct result of the more complete and efficient combustion that the unique airflow pattern achieves.
330 lbs of stones - over 30 minutes of steam after the fire
At 330 lbs (150 kg), the HIVE Flow LS holds the largest primary stone capacity in the HUUM HIVE Flow lineup. The large stone mass accumulates substantial thermal energy during the fire and holds it long after the fire dies down. HUUM's own description of the steam performance: full sauna bathing even over 30 minutes after the fire has died. For a sauna session managed from outside via the LS configuration - where the fire is loaded and then left to burn - the stone thermal mass is what sustains the session quality long after the fire itself has burned down. The optional HUUM stone cage adds a further 77-88 lbs of capacity for sessions requiring the maximum stone thermal reserve.
5.9" side and back clearances - snug installation possible
The HIVE Flow LS requires just 150mm (5.9") at the sides and back from combustible materials - the same tight clearances as the HIVE Flow Mini, achieved by the same patent-pending furnace design. HUUM attributes the minimal clearances directly to the Flow furnace: the heater warms up more evenly across its body, preventing localised hot spots that would otherwise require larger standoffs from combustible wall surfaces. The front clearance is 500mm (19.7"). No protective sheath or shield is required to achieve these clearances. For a sauna room where the stove position is close to wooden bench legs and wall panels, 5.9" side clearances offer significantly more layout flexibility than conventional stoves.
BImSchV and CPR certified - independently verified emissions
The HIVE Flow LS meets the BImSchV Stufe 2 standard - the rigorous German clean combustion regulation - and carries CPR (European Commission) certification. These are independently verified emission and performance values, not manufacturer self-declarations. The CO value of 346 mg/m3 and PM value of 25 mg/m3 are confirmed by testing under these standards. HUUM states that the HIVE Flow surpasses all known efficiency and environmental metrics for wood-burning stoves of its class. For buyers who require certified emission compliance for installation approval, or who simply want verified evidence of the stove's environmental performance, these certifications are the documented record.
HIVE Flow Series - LS and related configurations
The H1016012 is the 9.8kW LS (firebox extension) configuration of the HIVE Flow platform. The same Flow furnace is available as: HIVE Flow (9.8kW, standard interior firebox, H1015012), HIVE Flow Mini (8.5kW, standard interior firebox, H1015012 variant), and HIVE Flow Mini LS (8.5kW, LS firebox extension, H1017012). All four share the same patent-pending Flow furnace (75% heat retention, CO 346 mg/m3, PM 25 mg/m3, 150mm side and back clearances), 5mm/3mm stainless steel construction, BImSchV and CPR certifications, and 5-year limited warranty. The HIVE Flow and HIVE Flow LS cover the 282-635 cu ft range at 9.8kW. The HIVE Flow Mini and Mini LS cover the 212-494 cu ft range at 8.5kW. Designed and made in Estonia by HUUM. We are an authorized HUUM dealer.
About HUUM
Designed in Estonia - BImSchV Certified - HIVE Flow Series - LS Firebox Extension
HUUM HIVE Flow LS. 9.8kW. 282-635 cu ft. 330 lbs of stones. 75% heat retention. Exterior loading.
HUUM is an Estonian sauna heater company. The HIVE Flow LS is the 9.8kW through-wall firebox configuration of the HIVE Flow platform - 330 lbs of stones, patent-pending Flow furnace (75% heat retention, CO 346 mg/m3, PM 25 mg/m3, 150mm side and back clearances), large glass door facing the adjacent room, and steam that lasts over 30 minutes after the fire dies. BImSchV and CPR certified. 330 lbs stones (10 boxes) and chimney connection required and sold separately. Pallet delivery. We are an authorized HUUM dealer.
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9.8kW wood-burning - 282-635 cu ft - LS firebox extension through sauna wall
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75% heat retention - CO 346 mg/m3 - PM 25 mg/m3 - lowest in category
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330 lbs stones required (10 boxes) - steam lasts over 30 min after fire
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5.9" side and back clearances - no protective sheath required
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BImSchV + CPR certified - 5-year warranty (excl. elements) - made in Estonia
HIVE Flow LS vs HIVE Flow Mini LS vs HIVE Wood LS 17 - HUUM exterior-feed stove comparison
HIVE Flow LS vs HIVE Flow Mini LS vs HIVE Wood LS 17 - choosing the right HUUM exterior-feed stove
Three HUUM exterior-feed wood-burning stoves serve different room sizes and efficiency priorities. HIVE Flow Mini LS H1017012: 8.5kW, 212-494 cu ft, 231 lbs stones (7 boxes), LS firebox extension, patent-pending Flow furnace (75% heat retention, CO 346 mg/m3). Right for smaller rooms from 212-494 cu ft where the Flow platform's efficiency and low emissions are the priority alongside exterior loading. HIVE Flow LS H1016012 (this listing): 9.8kW, 282-635 cu ft, 330 lbs stones (10 boxes), LS firebox extension, same Flow furnace. Right when the room is larger (282-635 cu ft) and the additional output and stone mass of the full HIVE Flow are required alongside exterior loading. HIVE Wood LS 17 H1010012: 17kW, 283-565 cu ft, 287 lbs stones (9 boxes), LS firebox extension, HUUM's stone-primary heat philosophy (different furnace approach, 5mm stainless steel flame tamer). Right when higher output (17kW) and the HUUM stone-primary experience are the priorities for a similar room range, with different efficiency and emissions characteristics than the Flow platform. Choose the HIVE Flow LS for the 282-635 cu ft range where 9.8kW Flow furnace efficiency and exterior loading via the LS extension are the right specification.
Manuals and Documents
Warranty
5-year limited warranty (excluding elements)
The HUUM HIVE Flow LS 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 unsuitable sauna stones (decorative stones in particular must not be used as they can break under heat), operating without the required stone load, or chimney-related damage from inadequate maintenance. The LS firebox bushing must pass through a non-combustible wall as specified in the installation manual. A licensed chimney professional is recommended for all flue installation and regular chimney sweep maintenance. Proof of purchase from an authorized HUUM dealer is required for warranty claims. We are an authorized HUUM dealer.
