Greetings, I'm a new member converting a large masonry chase into an alcove for a freestanding wood stove. I'm sharing my project here in hopes of getting feedback on several considerations: 1) stove position and insulation, 2) protecting a wooden mantel, 3) venting the lid, and 4) stove pipe clearances.
I purchased a Hearthstone Green Mountain 60 to heat less than 1200 sf of our 1980's home. Professional installation will include the stove, class A chimney and boiler flue and a new cap. I'll be doing most of the rest myself as part of a larger renovation including all interior and exterior surfaces. Aesthetic goals and the need to repair extensive water damage to the fireplace, framing, and masonry motivated us to gut the chase completely (see picture). The interior of the chase is approx. 20" deep by 80" wide.
I plan to keep everything in the walls noncombustible below the mantel and behind the columns. The walls will be thin stone veneer and plaster on durarock, supported by metal studs. The walls will be filled in with mineral wool insulation without any air gap. I'll describe some of the constraints, but I'd welcome any input on how to get more insulation directly behind the stove (or how big a concern that really is). I'm happy to have the stove set forward and use a pad for ember protection on the floor. As shown in the section, assuming an offset, the rear wall thickness seems to be constrained more by the stove pipe than the stove itself. It'd be nice to build the new walls plumb and level, but I could slope the rear surface parallel to the existing wall for a little extra space at the bottom (see note below). At the lid, the pipe will transition to a class A chimney within a 12" square chase extending about 2' up to a platform at the base of the second floor (from there it will continue to the cap through about 12' of unconditioned space in the chase). I plan to frame the lid structure of the alcove with wood unless noncombustible materials at this height would serve a purpose.
The biggest issue seems to be the wooden mantel. We would really like to use some sentimental old white oak beams reclaimed from a family home for the mantel and side supports. A metal heat shield should help us achieve enough vertical clearance above the stove (about 24"), but the mantel might be within 10" of the stove pipe. If the heat shield extends up the back as shown, is clearance still a concern? The overall mantel width is over 60" and the stove is 30" wide. How wide would the heat shield need to be?
The top of the alcove has nearly 16" of vertical space behind the mantel. I plan to install horizontal vents at each end of the alcove which will extend upwards to exit the face near the ceiling. By default, the grills would each be 6" tall by 14" wide, but the throats would only be 3-1/4". Does this seem like enough ventilation? I could widen the intakes in the alcove, but aesthetics are a constraint on the face.
Thanks in advance for any input. I've really benefitted from the knowledge already shared here and tried to summarize what I've learned about alcove construction in a separate post to offer an easier starting point for others.
Note: the exterior wall of the chase is only 4" block with cultured stone veneer and was built as much as 5" out of plumb over 20'. This seems to be because the house itself was built almost 3" out of plumb and they bellied out the wall in the middle to accommodate the masonry/tile chimney. Removing this weight and the 8" concrete cap was another reason for gutting everything. The chase is built on a poured concrete foundation wall. The chase is not mechanically connected to the framing, yet there was no separation between the masonry and house siding. No one we've consulted has raised enough concern not to leave it as is (apart from some repairs to the upper courses) and to run new fabricated flues through it.)
![[Hearth.com] Large masonry fireplace to alcove conversion](https://www.hearth.com/talk/data/attachments/340/340203-8f51505414abaf53c1791e386f231b21.jpg?hash=YVh9PbBVcN "[Hearth.com] Large masonry fireplace to alcove conversion")
![[Hearth.com] Large masonry fireplace to alcove conversion](https://www.hearth.com/talk/data/attachments/340/340204-59c86c44f4fcd1c2859a721a9d88f1fc.jpg?hash=dfTcO-oA5I "[Hearth.com] Large masonry fireplace to alcove conversion")
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![[Hearth.com] Large masonry fireplace to alcove conversion](https://www.hearth.com/talk/data/attachments/340/340206-6bd1a831d84d0d8ab1e57b535e2b2fd2.jpg?hash=Nt041KCKIa "[Hearth.com] Large masonry fireplace to alcove conversion")
I purchased a Hearthstone Green Mountain 60 to heat less than 1200 sf of our 1980's home. Professional installation will include the stove, class A chimney and boiler flue and a new cap. I'll be doing most of the rest myself as part of a larger renovation including all interior and exterior surfaces. Aesthetic goals and the need to repair extensive water damage to the fireplace, framing, and masonry motivated us to gut the chase completely (see picture). The interior of the chase is approx. 20" deep by 80" wide.
I plan to keep everything in the walls noncombustible below the mantel and behind the columns. The walls will be thin stone veneer and plaster on durarock, supported by metal studs. The walls will be filled in with mineral wool insulation without any air gap. I'll describe some of the constraints, but I'd welcome any input on how to get more insulation directly behind the stove (or how big a concern that really is). I'm happy to have the stove set forward and use a pad for ember protection on the floor. As shown in the section, assuming an offset, the rear wall thickness seems to be constrained more by the stove pipe than the stove itself. It'd be nice to build the new walls plumb and level, but I could slope the rear surface parallel to the existing wall for a little extra space at the bottom (see note below). At the lid, the pipe will transition to a class A chimney within a 12" square chase extending about 2' up to a platform at the base of the second floor (from there it will continue to the cap through about 12' of unconditioned space in the chase). I plan to frame the lid structure of the alcove with wood unless noncombustible materials at this height would serve a purpose.
The biggest issue seems to be the wooden mantel. We would really like to use some sentimental old white oak beams reclaimed from a family home for the mantel and side supports. A metal heat shield should help us achieve enough vertical clearance above the stove (about 24"), but the mantel might be within 10" of the stove pipe. If the heat shield extends up the back as shown, is clearance still a concern? The overall mantel width is over 60" and the stove is 30" wide. How wide would the heat shield need to be?
The top of the alcove has nearly 16" of vertical space behind the mantel. I plan to install horizontal vents at each end of the alcove which will extend upwards to exit the face near the ceiling. By default, the grills would each be 6" tall by 14" wide, but the throats would only be 3-1/4". Does this seem like enough ventilation? I could widen the intakes in the alcove, but aesthetics are a constraint on the face.
Thanks in advance for any input. I've really benefitted from the knowledge already shared here and tried to summarize what I've learned about alcove construction in a separate post to offer an easier starting point for others.
Note: the exterior wall of the chase is only 4" block with cultured stone veneer and was built as much as 5" out of plumb over 20'. This seems to be because the house itself was built almost 3" out of plumb and they bellied out the wall in the middle to accommodate the masonry/tile chimney. Removing this weight and the 8" concrete cap was another reason for gutting everything. The chase is built on a poured concrete foundation wall. The chase is not mechanically connected to the framing, yet there was no separation between the masonry and house siding. No one we've consulted has raised enough concern not to leave it as is (apart from some repairs to the upper courses) and to run new fabricated flues through it.)
