The Harvia Pro 36 Duo is a 31kW wood-burning sauna stove and fireplace combination for rooms from 494 to 1,271 cubic feet. DUO means the glass hatch is wall-embedded and faces the adjacent room - firewood is loaded from outside the sauna, ash is removed from outside, and the fire burns behind the glass hatch visible from the adjacent space as a working fireplace. Inside the sauna, bathers receive the full 31kW output and the steam from 132.3 lbs of AC3020 stones without the sauna door ever opening. Harvia's description is precise: the fire behind the glass hatch of the wood-burning heater creates the atmosphere of the fireplace in a room next to the sauna and allows you to heat the sauna from outside. The outer shell of the Pro 36 Duo is stainless steel - different from the graphite black exterior of the standard PRO 36. The DUO configuration also creates more space in the sauna room and allows more freedom when choosing sauna bench solutions, since the firebox access and ash removal are handled entirely from the adjacent space. A chimney-mounted water tank can be added separately. Flue: 115mm (4.5") top connection - a 6" North American adapter is required and sold separately. 132.3 lbs AC3020 stones (3 boxes, 10-15 cm) required and sold separately. Pallet delivery - scheduled freight appointment required. CE and EAC certified. Made in Finland by Harvia.
DUO - fireplace in the adjacent room, sauna heat inside, one fire
The PRO 36 Duo's defining feature is the same as all Harvia DUO stoves: two simultaneous experiences from a single fire. The glass hatch is wall-embedded and faces the adjacent room - the person in that room sees the live fire behind the glass as a direct fireplace experience and loads the wood from their side. Inside the sauna, bathers receive the 31kW heat output and the steam from a fully charged 132.3-lb stone bed, with the sauna door staying closed and the session uninterrupted throughout. Ash removal is also done from outside the sauna, so the sauna interior stays clean. Harvia adds a specific benefit of the DUO that applies directly to the sauna room design: the DUO heater creates more space in the sauna and allows more freedom when deciding sauna bench solutions. With the firebox and ash box access fully external, the sauna room can be laid out as if the stove has no user-side access requirements at all.
Stainless steel outer shell - different from the standard PRO 36
The Pro 36 Duo's outer shell is stainless steel, not the graphite black of the standard PRO 36 (WKPR36M). This is a key visual and material difference between the two models. Stainless steel resists heat discolouration and is easy to clean without special treatment - relevant for the portion of the stove body that is visible in the adjacent room as part of the fireplace presentation. The large steel-framed glass door faces the adjacent room. The fire visible through the glass illuminates the adjacent space with the warm light of a working fire. For a combined sauna and lounge space where the visible side of the stove is the fireplace face in the lounge, the stainless steel finish integrates with a wider range of interior aesthetics than a painted surface would.
31kW for 494 to 1,271 cu ft - same output and room range as PRO 36, extended depth
The Pro 36 Duo shares the complete 31kW output and 494-1,271 cu ft room range of the standard PRO 36 platform. Stone capacity is 132.3 lbs (3 boxes AC3020, 10-15 cm) - same as the standard PRO 36. The safety clearances to combustible materials are 19.69" on all sides - same as the standard PRO 36. The key dimensional difference is depth: 31.1" for the DUO vs 20.08" for the standard PRO 36, due to the wall-penetrating DUO fire chamber extension. The maximum firewood length is 15.3" (390mm) with a diameter of 3" to 6" (80-150mm). Adjustable feet make installation levelling straightforward. A licensed chimney professional is recommended for all flue installations. The wall penetration for the DUO configuration requires correct preparation per the installation manual before delivery.
31kW wood-burning sauna stove and fireplace combo for rooms from 494 to 1,271 cubic feet. PRO 36 DUO - wall-embedded glass hatch faces adjacent room. Firewood loaded from outside, ash removed from outside. Fire creates fireplace atmosphere in adjacent room while sauna bathers enjoy 31kW heat inside. DUO creates more space in sauna - more freedom for bench layouts. No electricity required. Stainless steel outer shell. Large steel-framed glass door faces adjacent room. 132.3 lbs AC3020 stones required (3 boxes, 10-15 cm, sold separately). Safety distances: 19.69" all sides (combustible). 3.94" sides and back (non-combustible). Ceiling 4.1 ft. Top flue connection (115mm) - 6" adapter required for North America (sold separately). Max firewood 15.3" / 3-6" diameter. Dimensions: 20.08"W x 31.1"D x 3.41 ft H. Optional: WL550 protective sheath, chimney-mounted water tank. Pallet delivery - scheduled freight required. 2-year warranty (consumer). CE and EAC certified. Made in Finland by Harvia.
31 kW 494 to 1,271 cu ft PRO 36 DUO - wall-embedded glass hatch faces adjacent room Firewood and ash handled from outside the sauna Fireplace atmosphere in adjacent room DUO creates more sauna space - bench layout freedom Stainless steel outer shell Large steel-framed glass door Wood-burning - no electricity required 132.3 lbs AC3020 stones required (3 boxes, 10-15 cm) Safety: 19.69" all sides (combustible) Top flue connection - 115mm 115mm flue - 6" adapter required for North America Max firewood 15.3" / 3-6" diameter 20.08"W x 31.1"D x 3.41 ft H WL550 protective sheath compatible Chimney-mounted water tank compatible Pallet delivery required 2-year warranty (consumer) CE and EAC certified - made in Finland
⚠️ 132.3 lbs AC3020 stones (3 boxes, 10-15 cm) required - not included. 6" North American flue adapter required - not included. Pallet delivery. Stones and the 6" adapter must be purchased separately. An additional box of stones is recommended for selection of best-fitting stones. This stove ships by scheduled pallet freight - a delivery appointment is required. At 176.4 lbs net weight, plan for on-site assistance to move the stove from the pallet delivery point to its installation position. The wall penetration for the DUO fire chamber must be correctly prepared per the installation manual before the stove is delivered. A licensed chimney professional is recommended for all flue installations.
ℹ️ PRO 36 Duo WKPR36DUOS vs PRO 36 WKPR36M - DUO exterior access vs standard interior access, same 31kW platform. PRO 36 WKPR36M: standard interior-access configuration - firebox and ash box face into the sauna room, wood loaded and ash removed from inside, graphite black exterior, 20.08" depth. Choose if interior firebox access is acceptable and a fireplace view in an adjacent room is not a goal. PRO 36 Duo WKPR36DUOS (this listing): DUO exterior-access configuration - wall-embedded glass hatch faces adjacent room, firewood and ash handled from outside, stainless steel exterior, 31.1" depth. More freedom for bench layout in sauna room. Choose if exterior firebox access, undisturbed sauna sessions, and a fireplace experience in an adjacent room are the installation goals. Both share identical output (31kW), room range (494-1,271 cu ft), stone requirement (132.3 lbs, 3 boxes AC3020), safety clearances (19.69" all sides combustible), and WL550 compatibility.
Specifications
Performance
| Power output |
31 kW |
| Fuel type |
Wood - no electricity required |
| Room volume |
494 to 1,271 cu ft (14-36 m3) |
| Stone capacity |
132.3 lbs / 60 kg (3 boxes AC3020, 10-15 cm) - sold separately |
| Stone size |
O 10-15 cm (AC3020) |
| Max firewood length |
15.3 in (390 mm) |
| Firewood diameter |
3 in to 6 in (80-150 mm) |
DUO configuration
| Glass hatch position |
Wall-embedded, faces adjacent room |
| Firewood loading |
From outside the sauna - adjacent room or exterior |
| Ash removal |
From outside the sauna |
| Fireplace effect |
Fire visible from adjacent room as live fireplace |
| Sauna space benefit |
More room and bench layout freedom - no firebox access needed inside |
| Outer shell |
Stainless steel (vs graphite black on standard PRO 36) |
Safety distances (combustible materials)
| Front |
19.69 in (500 mm) |
| Left side |
19.69 in (500 mm) |
| Right side |
19.69 in (500 mm) |
| Back |
19.69 in (500 mm) |
| Ceiling clearance |
4.1 ft (1,250 mm) above stove top |
| Side / back (non-combustible) |
3.94 in (100 mm) |
| Front (non-combustible) |
19.69 in (500 mm) |
| Minimum room ceiling height |
6.56 ft (2,000 mm) |
Physical dimensions
| Width |
20.08 in (510 mm) |
| Depth (extended for DUO wall) |
31.1 in (790 mm) |
| Height |
3.41 ft (1,040 mm) |
| Net weight (stove only) |
176.4 lbs (80 kg) |
| Gross weight (packaged) |
177.5 lbs (80.5 kg) |
PRO 36 Duo vs PRO 36 - key differences
| Firebox access |
DUO: From outside | PRO 36: From inside sauna |
| Glass hatch faces |
DUO: Adjacent room | PRO 36: Into sauna room |
| Outer shell |
DUO: Stainless steel | PRO 36: Graphite black |
| Depth |
DUO: 31.1 in | PRO 36: 20.08 in |
| Net weight |
DUO: 176.4 lbs | PRO 36: 154.3 lbs |
| Output, room range, stones |
Identical - 31kW, 494-1,271 cu ft, 132.3 lbs (3 boxes) |
| Safety distances, flue |
Identical |
Flue, certifications, and optional accessories
| Flue connection diameter |
115mm (4.5") - standard European |
| Flue connection position |
Top connection |
| North American adapter |
6" (155mm) adapter required - sold separately |
| Certifications |
CE / EAC certified |
| Origin |
Made in Finland by Harvia |
| Warranty |
2-year limited (consumer use) |
| Protective sheath |
Harvia WL550 (specific to PRO 36 / PRO 36 Duo) |
| Water heater |
Chimney-mounted water tank (sold separately) |
| Delivery |
Scheduled pallet freight - appointment required |
What's included
Harvia Pro 36 Duo wood-burning sauna stove with wall-embedded DUO glass hatch
Large steel-framed glass door
Frame
Grill
Adjustable feet
Installation and operating instructions
2-year limited warranty (consumer use)
Required (not included): 132.3 lbs AC3020 stones - 3 boxes, 10-15 cm (additional box recommended); 6" North American flue adapter (Harvia WZ115155). Optional accessories (sold separately): WL550 protective sheath (specific to PRO 36 / PRO 36 Duo); chimney-mounted water tank; flue pipe extensions. A licensed chimney professional is recommended for all flue installations. Wall penetration preparation required per installation manual before delivery.
Why the Harvia Pro 36 Duo stands out
Fireplace and sauna - one fire, two rooms
The PRO 36 Duo creates two simultaneous experiences from a single fire. In the adjacent room: the large steel-framed glass hatch provides a direct view of the burning fire - the warmth, light, and atmosphere of a working fireplace. In the sauna: 31kW of wood heat charges 132.3 lbs of AC3020 stones, producing dense, consistent steam for a large group bathing session. Both experiences run simultaneously from a single fire that is tended entirely from the adjacent room side - no interaction with the sauna interior required from anyone. For a combined sauna and lounge, a cabin with an adjoining relaxation room, or any layout where the fire should be accessible and visible from outside the sauna, the PRO 36 Duo delivers both without compromise.
More space in the sauna - more bench layout freedom
Harvia directly identifies this as a benefit of the DUO configuration: the DUO heater creates more space in the sauna and allows more freedom when deciding sauna bench solutions. When the firebox faces into the sauna, a loading space in front of the stove and an approach path must be preserved for wood handling and ash removal. When the firebox faces outside, the sauna-side of the stove has no operational requirements - the wall around the stove can be treated like any other wall surface for bench placement purposes. In a large sauna room from 494 to 1,271 cu ft where optimising bench area is a design priority, the DUO layout directly increases usable bench space.
Undisturbed sessions - firewood and ash from outside
Loading wood from outside the sauna room means the firebox can be tended, wood added, and the fire adjusted without opening the sauna door, losing heat, or disturbing the bathing session. Ash removal is equally external - the ash box is accessed from the adjacent room side. In a large sauna serving a group over multiple rounds of bathing, the ability to manage the fire from outside means one person can maintain the fire from the lounge or corridor while bathers inside are in session. Harvia states this benefit plainly: adding firewood from outside the sauna is easy and keeps the sauna room clean.
31kW - great baths for a great group
Harvia's own tagline for the PRO 36 platform is direct: great baths for a great group of people. At 31kW for rooms from 494 to 1,271 cu ft, the PRO 36 Duo is positioned for large sauna rooms where the session involves multiple bathers in rounds and the stove must sustain heat and steam throughout. The 132.3-lb stone load accumulates substantial thermal energy during the fire and holds it long after the fire dies down - Harvia notes that even if the fire goes out temporarily, the residual heat from the stones keeps the sauna comfortable. The stainless steel air-flow spoiler built into the PRO 36 platform improves combustion efficiency and heat transfer to the stone mass.
Stainless steel outer shell - visible in the adjacent room
The Pro 36 Duo's outer shell is stainless steel - the surface that is visible in the adjacent room as the fireplace face of the stove. Stainless steel is durable, resists heat discolouration over years of use, and is easy to clean and maintain. The large steel-framed glass door is set into the stainless steel front face, presenting the fire clearly and cleanly. For a lounge or relaxation space where the visible side of the stove needs to be presentable and easy to keep in good condition across years of daily use, the stainless steel exterior is the appropriate specification. The WL550 protective sheath (sold separately, specific to PRO 36 and PRO 36 Duo) can be installed to reduce side and back clearances further when the room layout requires it.
PRO Series DUO platform - Pro 36 Duo and related configurations
The WKPR36DUOS is the DUO exterior-access configuration of Harvia's PRO 36 platform. The same 31kW platform is available in standard interior-access (PRO 36, WKPR36M). The Pro Series also includes the PRO 20 platform (24.1kW, 283-706 cu ft) in standard (WKPR20M), DUO (PRO 20 Duo), SL exterior-feed (WKPR20SLM), right-side water tank (PRO 20 RS), and left-side water tank (PRO 20 LS) configurations. The chimney-mounted water tank accessory can be added to the PRO 36 Duo for hot water heating simultaneously with the sauna. CE and EAC certified. Made in Finland by Harvia. We are an authorized Harvia dealer.
About Harvia
Made in Finland - CE Certified - Pro Series DUO - Stainless Steel
Harvia Pro 36 Duo. 31kW. 494-1,271 cu ft. DUO - fire loads from outside, fireplace view in adjacent room.
Harvia is a Finnish sauna and spa company established in 1950. The Pro 36 Duo is the DUO exterior-access configuration of the 31kW PRO 36 platform - a wall-embedded glass hatch facing the adjacent room creates a fireplace experience outside while 31kW heats the sauna inside. Stainless steel outer shell, large steel-framed glass door, firewood and ash handled from outside, more bench layout freedom in the sauna room. 132.3 lbs AC3020 stones (3 boxes) and a 6" North American flue adapter are required and sold separately. Pallet delivery. We are an authorized Harvia dealer.
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31kW wood-burning - 494-1,271 cu ft - no electricity required
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DUO - wall glass hatch faces adjacent room - firewood and ash from outside
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Stainless steel outer shell - large steel-framed glass door - fireplace atmosphere
- Safety distances: 19.69" all sides (combustible) - 3.94" sides/back (non-combustible)
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132.3 lbs AC3020 stones (3 boxes) required - 6" adapter required - both sold separately
PRO 36 Duo vs PRO 36 vs PRO 20 SL - exterior access stove comparison
PRO 36 Duo vs PRO 36 vs PRO 20 SL - exterior access vs interior access stove selection
Three Pro Series configurations are relevant for buyers considering the PRO 36 Duo. PRO 36 WKPR36M: same 31kW platform, interior access - firebox and ash box face into the sauna, graphite black exterior, 20.08" depth, wood loaded and ash removed from inside. Choose if interior firebox access is acceptable and no fireplace view in an adjacent room is needed. PRO 36 Duo WKPR36DUOS (this listing): 31kW, 494-1,271 cu ft, DUO exterior access, stainless steel exterior, 31.1" depth, wall glass hatch faces adjacent room, firewood and ash from outside, more bench layout freedom. Choose for the 494-1,271 cu ft range where exterior firebox access, undisturbed sessions, and a fireplace in an adjacent room are the goals. PRO 20 SL WKPR20SLM: 24.1kW, 283-706 cu ft, exterior feed, cast-iron glass door faces adjacent room, 88 lbs stones (2 boxes AC3020), 4" side clearances. Choose for the 283-706 cu ft room range where 24.1kW and the SL exterior-feed configuration are the right specification, with tighter side clearances than the PRO 36 Duo.
Manuals and Documents
Warranty
2-year limited warranty (consumer use)
The Harvia Pro 36 Duo is covered by Harvia's 2-year limited warranty from the date of purchase for consumer use. The warranty covers defects in manufacturing and materials under normal use conditions. The warranty does not cover damage caused by improper installation, use of incorrect stone type or size (non-AC3020, or stones outside the 10-15 cm specified diameter range), operating without the required stone load, failure to follow the installation and operating guidelines in the manual, damage from inadequate chimney maintenance, soot fires, or improper wall penetration preparation for the DUO fire chamber configuration. A licensed or certified chimney professional is recommended for all flue installation and regular chimney sweep maintenance. Proof of purchase from an authorized Harvia dealer is required for warranty claims. We are an authorized Harvia dealer.
