Outside Feed Wood Sauna Stoves

How an outside feed wood stove works

Outside feed wood sauna stoves are also called external feed or through-the-wall stoves. In HUUM's manual drawing of the HIVE Flow LS, the stove and its stones sit in the sauna and the firebox door is on the far side of a non-combustible wall.

Where the fire can be fed from differs by model:

• Choose Harvia's M3 SL, Legend 150 SL or Legend 240 SL if the fire is to be fed from outdoors: Harvia offers each of the three for heating the sauna from another room or from outside the building, while its Pro 20 SL, Pro 20 Duo and Pro 36 Duo, like HUUM's LS stoves here, are described for loading from the room next to the sauna.
• For a fire fed from a changing room or another room beside the sauna, choose by room size and maker instead: every outside feed model here is described for loading from another room.
• Rule out the HIVE Wood 13 and the plain HIVE Wood 17 if the fire must be fed from outside the sauna room: HUUM's manual loads those two from inside and keeps firing from another room for the HIVE Wood 17 LS, which the HUUM HIVE Wood Series listing also sells.

Outside feed or inside loading for a wood sauna stove

Outside feed and inside-loading wood stoves differ in which room the fire is fed from. Harvia's Pro 20 Duo and Pro 36 Duo show the outside feed side: firewood goes in and ash comes out in the room next to the sauna, where a glass hatch shows the fire.

• Choose an outside feed wood sauna stove if the firewood should stay out of the room you bathe in.
• Rule out HUUM's LS stoves here, Harvia's Duo models and the Legend 240 SL where the wall the stove passes through cannot be made non-combustible: HUUM's manuals put the LS stoves through a non-combustible wall, and Harvia's carry the nonflammable wall up to the roof for its Duo models and the Legend 240 SL, and for the Legend 150 SL and M3 SL when they connect to a Harvia steel chimney. For the Pro 20 SL, check the wall its manual asks for before choosing.
• Choose a stove loaded inside the sauna if carrying firewood into the hot room is no drawback: compare those among wood burning sauna heaters.

Sizing an outside feed wood sauna stove to the sauna room

An outside feed wood sauna stove is sized to the room's inside volume, length by width by height, read against the minimum and maximum its maker prints for the model.

Harvia's sizing rule and HUUM's HIVE Flow manual add room volume for uninsulated walls. Harvia counts every square foot of uninsulated brick, glass block, glass, concrete or tile wall, a glass door among them, as about 3.9 more cubic feet, and a solid-log room as 1.5 times its measured volume. In HUUM's HIVE Flow manual, every uninsulated square foot of brick, tile or glass wall adds about 3.3 cubic feet.

• For a room from 212 cubic feet to just under 282, start with Harvia's M3 SL or Legend 150 SL or HUUM's HIVE Flow Mini LS, all rated from 212; every other outside feed model here is rated from 282 or more.
• Above 459 cubic feet, rule out the M3 SL and Legend 150 SL, which Harvia rates to 459; the HIVE Flow Mini LS drops out above 494, the HIVE Wood 17 LS above 565 and the HIVE Flow LS above 635.
• Above 706 and up to 848 cubic feet, choose between Harvia's Legend 240 SL and Pro 36 Duo, the two stoves here rated past 706; above 848 and up to 1,271, the Pro 36 Duo is the one rated for the room.
• Under 212 or above 1,271 cubic feet, rule out this collection: no outside feed stove here is rated for such a room.

Harvia and HUUM outside feed wood sauna stoves compared

Harvia makes six of the stoves here, from 16 to 31 kW; HUUM makes the other three stoves here, from 8.5 to 17 kW, and Topture's three packages here are built on HUUM's LS stoves.

• Choose HUUM's HIVE Flow LS or HIVE Flow Mini LS if the stove must join a flue that already serves a fireplace: HUUM's manual allows it after checking with the local authorities and fire department, while Harvia's manuals call each of its stoves here unsuitable for a shared flue and HUUM's HIVE Wood manual requires a separate one.
• To stay with one brand, browse Harvia wood burning sauna heaters or HUUM wood burning sauna stoves.

Installing an outside feed wood sauna stove: what ships, chimney and floor

None of the nine stove-only listings here comes with sauna stones or a chimney, by the makers' delivery lists, Bathing Brands (Harvia's US distributor) and, for the M3 SL and Pro 20 SL chimneys, Topture's own listings.

The three HUUM packages here add the stones and the HUUM chimney kit chosen with the package, and the two HIVE Flow packages also carry an LS protective bedding.

• Choose a HUUM package if you would rather order the stove, its stones and the chimney kit together.
• Choose a stove alone if a suitable chimney is already in place or you are buying it separately, and add sauna stones to the order.

Harvia's manuals give each of its stoves here a single upper connection opening, 4.5 in (115 mm) across, for a T600 chimney. HUUM's HIVE Flow LS models connect at the top or the back through a 4.5 in (114 mm) chimney leg, for a T450 chimney, and only a certified installation expert may make that connection; the HIVE Wood's outlet is on top, 4.53 in (115 mm) across, for a T600 chimney, and HUUM leaves that connection to a specialist. Your installer takes the clearances and the chimney route from the stove's own manual.

• If the floor in front of the firebox door, on the loading side, is combustible, plan its protection with the stove: Harvia's manuals ask for nonflammable protection there, HUUM's HIVE Flow manual for a sheet-metal plate and its HIVE Wood manual for fire-resistant protection in front of the HIVE Wood 17 LS, and none of the three HUUM packages here includes it.

Freight on all 12 listings here is included within the contiguous United States, and Topture insures each freight shipment for its full value; for a damage claim, note the damage on the Bill of Lading at delivery. Topture is an authorized Harvia retailer and an authorized HUUM retailer, listed as an E-shop in HUUM's official dealer directory; the sauna heaters hub explains how buying a heater from Topture works.

Outside feed wood sauna stove: next steps for the chimney, a package or room sizing

• Ordering the stove alone: the product page of every stove here offers its maker's chimney kits as add-ons; for chimney kits on their own, see sauna chimney kits.
• Comparing wood stoves sold as packages: see wood burning sauna heater packages.
• Unsure which range your room falls in once glass or log walls are counted: Topture's Lifetime Expert Support works it out with you on (833) 419-1774, by live chat or at contact@topture.com.

Reviewed October 2026