The Harvia M3 SL is a 16.5kW wood-burning sauna stove for rooms from 212 to 459 cubic feet with an exterior-feed fire chamber that passes through the sauna wall. The stove body, stone cage, and heat are inside the sauna. The fire chamber extends through the wall so wood is loaded from an adjacent room or from outdoors - the cast-iron glass door faces outward, giving the person in the adjacent room a direct view of the burning fire while bathers inside the sauna enjoy the heat undisturbed. The door opening direction is reversible, set during installation to suit the room layout. Harvia's own description of this model captures the experience precisely: while one bather is still sitting in the sauna, the other one can cook sausages over the fire or watch the fire glowing behind the cast-iron-framed glass door. The M3 SL provides great steam in small and medium-sized saunas. 66 lbs of AC3020 stones (2 boxes, 10-15 cm) are required and sold separately. A pipe model chimney-mounted water heater can be added separately. Flue: 115mm (4.5") top connection - a 6" North American adapter is required and sold separately. CE and EAC certified. Made in Finland by Harvia.
SL exterior feed - two rooms, one fire, one stove
The M3 SL is Harvia's smallest and most compact exterior-feed wood-burning sauna stove. It brings the dual-room SL capability to the 212-459 cu ft small sauna range - the same range as the standard M3, but with the firebox facing outward rather than into the sauna room. The M3 SL is designed specifically for people who want to conveniently heat their sauna from another room or outside the building, in Harvia's own words. The stove body sits in the sauna. The fire chamber collar extension (220mm / 8.66") passes through the wall. On the adjacent side, the cast-iron glass door provides the live fire view. The warmth, atmosphere, and activity of fire tending happen in the adjacent room. The sauna itself receives the 16.5kW heat output and the steam from 66 lbs of stones, with the sauna door staying closed and the session uninterrupted throughout.
Classic M Series design - the smallest exterior-feed Harvia stove
The M3 SL uses the same compact M Series body as the standard M3 - at 15.35"W x 16.93"D (plus the 8.66" wall collar) x 27.95"H, it is Harvia's narrowest and lightest exterior-feed wood-burning stove. This makes it suited for small sauna installations where the wall penetration footprint must be kept as compact as possible, or where the overall installation space is constrained. The WL450 protective sheath (sold separately, specific to M1, M2, M3, and M3 SL) can be installed to reduce safety clearances from the standard 11.81" on all sides to further reduced distances when the room layout requires it. Adjustable legs allow the stove to be levelled on any floor surface. The pipe model water heater (sold separately) can be added to the chimney pipe to heat bathwater simultaneously with the sauna.
Reversible door direction - set at installation
The cast-iron glass door opening direction on the M3 SL is reversible - set during installation to open left or right to suit the access direction from the adjacent room. No specific handed configuration needs to be specified at the time of purchase. The door can be changed to either swing direction during installation without ordering a separate part. Maximum firewood length is 13.75" (350mm) with a diameter up to 6". Top flue connection only. All Harvia wood-burning stoves use the 115mm (4.5") European standard flue outlet; a 6" (155mm) North American adapter is required and sold separately. A licensed or certified chimney professional is recommended for all flue installations. The wall penetration for the SL collar must be correctly prepared per the installation manual and Additional Instructions document before the stove is installed.
16.5kW wood-burning sauna stove with exterior feed for rooms from 212 to 459 cubic feet. SL - fire chamber extends through sauna wall, wood loaded from adjacent room or outdoors. Cast-iron glass door faces outward - fireplace view from adjacent room while sauna bathers enjoy heat inside. Reversible door direction. No electricity required. 66 lbs AC3020 stones required (2 boxes, 10-15 cm, sold separately). Safety distances: 11.81" front, sides and back (combustible). Ceiling clearance 3.94 ft. Top flue connection only. 115mm flue - 6" adapter required for North America (sold separately). Max firewood 13.75" / up to 6" diameter. Dimensions: 15.35"W x 16.93"D + 8.66" collar x 27.95"H. Adjustable legs. WL450 protective sheath compatible (sold separately). Pipe model water heater compatible (sold separately). Pallet delivery - scheduled freight required. 2-year warranty (consumer). CE and EAC certified. Made in Finland by Harvia.
16.5 kW 212 to 459 cu ft SL - exterior feed through sauna wall Wood loaded from adjacent room or outdoors Cast-iron glass door faces outward - fireplace view Reversible door direction Wood-burning - no electricity required M Series compact design - smallest Harvia exterior-feed stove 66 lbs AC3020 stones required (2 boxes, 10-15 cm) Safety: 11.81" front, sides and back (combustible) Top flue connection - 115mm 115mm flue - 6" adapter required for North America Max firewood 13.75" / up to 6" diameter 15.35"W x 16.93"D + 8.66" collar x 27.95"H WL450 protective sheath compatible Pipe model water heater compatible Pallet delivery required 2-year warranty (consumer) CE and EAC certified - made in Finland
⚠️ 66 lbs AC3020 stones (2 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. The wall penetration for the SL fire chamber collar extension must be correctly prepared per the installation manual and the included Additional Instructions document before the stove is installed. A licensed chimney professional is recommended for all flue installations.
ℹ️ M3 SL WKM3SL vs M3 WKM3 - exterior feed vs interior feed, same M Series platform. M3 WKM3: standard interior-feed configuration - firebox door faces into the sauna room, wood loaded from inside the sauna. M3 SL WKM3SL (this listing): exterior-feed SL configuration - fire chamber collar extends through the sauna wall, wood loaded from adjacent room or outdoors, cast-iron glass door faces the adjacent room for a fireplace view, bathers inside the sauna are undisturbed. Both share identical output (16.5kW), room range (212-459 cu ft), stone requirement (66 lbs, 2 boxes AC3020), WL450 sheath compatibility, and pipe model water heater compatibility. Choose the M3 for interior-feed simplicity. Choose the M3 SL for exterior wood loading and the dual-room fireplace experience - Harvia's most compact SL stove for small saunas.
Specifications
Performance
| Power output |
16.5 kW |
| Fuel type |
Wood - no electricity required |
| Room volume |
212 to 459 cu ft (6-13 m3) |
| Stone capacity |
66 lbs / 30 kg (2 boxes AC3020, 10-15 cm) - sold separately |
| Stone size |
O 10-15 cm (AC3020) |
| Max firewood length |
13.75 in (350 mm) |
| Firewood diameter |
Up to 6 in |
SL exterior feed
| Firebox access |
From outside the sauna room via collar wall extension |
| Glass door |
Cast-iron framed - faces adjacent room |
| Door direction |
Reversible - set during installation |
| Wall collar extension |
8.66 in (220 mm) beyond stove body depth |
| Dual-room effect |
Sauna heat inside + fireplace view outside simultaneously |
Safety distances (combustible materials)
| Front |
11.81 in (300 mm) |
| Sides (left and right) |
11.81 in (300 mm) |
| Back |
11.81 in (300 mm) |
| Ceiling clearance |
3.94 ft (1,200 mm) above stove top |
| Minimum room ceiling height |
6.56 ft (2,000 mm) |
| With WL450 sheath |
Reduced - see Additional Instructions document |
Physical dimensions
| Width |
15.35 in (390 mm) |
| Depth (stove body) |
16.93 in (430 mm) |
| Collar extension (through wall) |
8.66 in (220 mm) |
| Total depth including collar |
25.59 in (650 mm) |
| Height |
27.95 in (710 mm) |
| Net weight (approx.) |
approx. 110 lbs (50 kg) |
Flue and installation
| Flue connection diameter |
115mm (4.5") - standard European |
| Flue connection position |
Top only |
| North American adapter |
6" (155mm) adapter required - sold separately |
| Legs |
Adjustable |
| Wall penetration |
Required per Additional Instructions document |
| Delivery |
Scheduled pallet freight - appointment required |
Certifications and optional accessories
| Certifications |
CE / EAC certified |
| Origin |
Made in Finland by Harvia |
| Warranty |
2-year limited (consumer use) |
| North American flue adapter |
Harvia WZ115155 (6" / 155mm) |
| Protective sheath |
Harvia WL450 (for M1, M2, M3, M3 SL) |
| Pipe model water heater |
Chimney-mounted, 22L tank (sold separately) |
What's included
Harvia M3 SL wood-burning sauna stove with SL exterior-feed collar
Cast-iron framed glass door (reversible direction)
Ash box
Adjustable legs
Installation and operation manual
Additional Instructions (SL wall penetration)
2-year limited warranty (consumer use)
Required (not included): 66 lbs AC3020 stones - 2 boxes, 10-15 cm (additional box recommended); 6" North American flue adapter (Harvia WZ115155). Optional accessories (sold separately): WL450 protective sheath (M1, M2, M3, M3 SL compatible); pipe model chimney-mounted water heater (22L). A licensed chimney professional is recommended for all flue installations. Wall penetration preparation required per the Additional Instructions document before installation.
Why the Harvia M3 SL stands out
Sauna and fireplace in one - the M Series SL experience
Harvia's own description of the M3 SL captures the experience directly: while one bather is still sitting in the sauna, the other one can cook sausages over the fire or watch the fire glowing behind the cast-iron-framed glass door. The SL configuration puts the fire at the centre of two room experiences simultaneously - the sauna room bathers receive 16.5kW of wood heat and the steam from 66 lbs of AC3020 stones, while the person in the adjacent room has a live cast-iron glass fire view and benefits from the warmth radiating from the firebox face. One fire, one stove, two completely different but connected experiences.
Harvia's most compact exterior-feed stove
The M3 SL is the smallest and narrowest exterior-feed wood-burning stove Harvia produces. At 15.35"W - the same compact width as the standard M3 - it brings the SL through-wall capability to sauna rooms and building layouts where larger exterior-feed stoves would be too wide or too heavy for the installation. For a cabin sauna with a small adjacent room or corridor, a sauna building where the wall space is limited, or any installation where a compact through-wall footprint is a priority, the M3 SL is the purpose-built specification. The collar extension of 8.66" through the wall is also the shortest SL extension in the Harvia lineup.
Undisturbed sessions - wood and ash from outside
Loading wood from outside the sauna room means the firebox can be tended and the fire maintained without opening the sauna door, losing heat, or disturbing the bathing session in any way. The sauna interior is kept clean because wood is never brought through the sauna room. For a small sauna with a lounge or relaxation area adjacent, one person can maintain the fire from outside while bathers in the sauna are in full session. The reversible door direction - set left or right swing at installation - means the firebox opening can be oriented for the most practical access direction from the adjacent space without ordering a specific handed configuration.
WL450 sheath - reduces clearances for tight rooms
The WL450 protective sheath (sold separately) is compatible with the M1, M2, M3, and M3 SL stoves. The standard M3 SL safety clearances of 11.81" on all sides from combustible materials are already modest for a wood-burning stove, but the WL450 reduces them further when the specific room layout requires it. For a small sauna room in the 212-459 cu ft range where bench placement near the stove is important and the wall clearances constrain bench position, the WL450 directly increases the usable bench area available. The sheath is a model-specific Harvia accessory designed to mount cleanly around the M Series body.
Pipe model water heater compatible
The M3 SL chimney pipe can be fitted with a Harvia pipe model water heater (sold separately), which mounts on the chimney above the stove and holds 22 litres of water. The smoke pipe runs through the tank and acts as a heat exchanger - water heats rapidly as the fire produces smoke through the pipe. By the time the sauna is at bathing temperature, the tank holds a full supply of hot water available for washing or post-session rinsing. For a cabin or outdoor sauna without separate hot water plumbing, the pipe model water heater on the M3 SL's chimney provides both sauna heating and hot water from a single wood-fired installation.
M Series platform - M3 SL in the Harvia M lineup
The WKM3SL is the exterior-feed SL variant of Harvia's M3 platform. The same 16.5kW, 212-459 cu ft platform is available as: standard interior feed (M3, WKM3) for installations where firebox access from inside the sauna is acceptable. The M Series (M1, M2, M3, M3 SL) is Harvia's classic compact stove lineup for small to medium saunas - the original platform that established Harvia's presence in the North American sauna market and remains in continuous production. For larger rooms needing exterior feed, the Legend 150 SL (WK150LDSL, 16kW, 212-459 cu ft, 264 lbs stones) provides the same room range with a much larger stone load. CE and EAC certified. Made in Finland by Harvia. We are an authorized Harvia dealer.
About Harvia
Made in Finland - CE Certified - M Series SL - Exterior Feed
Harvia M3 SL. 16.5kW. 212-459 cu ft. Exterior feed. Cast-iron glass door faces adjacent room.
Harvia is a Finnish sauna and spa company established in 1950. The M3 SL is the exterior-feed SL variant of Harvia's compact M3 platform - the most compact exterior-feed wood-burning stove in the Harvia lineup. Fire chamber collar extends through the sauna wall; cast-iron glass door faces the adjacent room for a live fireplace view while bathers inside enjoy the 16.5kW sauna heat undisturbed. 66 lbs AC3020 stones (2 boxes, 10-15 cm) and a 6" North American flue adapter are required and sold separately. Pallet delivery. We are an authorized Harvia dealer.
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16.5kW wood-burning - 212-459 cu ft - no electricity required
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SL exterior feed - wood from adjacent room - fireplace view outside sauna
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Cast-iron glass door - reversible direction - compact M Series body
- Safety distances: 11.81" front, sides and back (combustible)
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66 lbs AC3020 stones (2 boxes) required - 6" adapter required - both sold separately
M3 SL vs M3 vs Legend 150 SL - small sauna exterior feed comparison
M3 SL vs M3 vs Legend 150 SL - choosing the right stove for 212-459 cu ft
Three configurations serve the 212-459 cu ft range with different priorities. M3 WKM3: 16.5kW, 212-459 cu ft, interior feed - firebox door faces into the sauna, wood loaded from inside. Right choice when interior firebox access is acceptable and no fireplace view in an adjacent room is needed. M3 SL WKM3SL (this listing): 16.5kW, 212-459 cu ft, exterior feed, cast-iron glass door faces adjacent room, 66 lbs stones (2 boxes AC3020), 11.81" clearances all sides, Harvia's most compact exterior-feed stove. Right choice for small saunas where exterior wood loading and a fireplace view in an adjacent room are the goals, and the smallest possible exterior-feed footprint is needed. Legend 150 SL WK150LDSL: 16kW, 212-459 cu ft, exterior feed, cast-iron glass door faces adjacent room, 264 lbs stones (6 boxes AC3020), 7.87" side clearances. Right choice when the same room range and exterior feed are needed but maximum stone mass (264 lbs vs 66 lbs) and longer sustained heat after the fire are the priority. The M3 SL is lighter, more compact, and easier to handle than the Legend 150 SL. The Legend 150 SL provides four times the stone mass for a deeper, more sustained heat.
Manuals and Documents
Warranty
2-year limited warranty (consumer use)
The Harvia M3 SL 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 or the Additional Instructions for the SL wall penetration, damage from inadequate chimney maintenance, or soot fires. 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.
