Protected Alcove Design

[overlandsea]

Decided this should just be a new thread...So long time since I posted, but I was finally able to get a Hearthstone Shelburne, and am going to start working on making the protected alcove! I'm really excited about this project!

One (of I'm sure many) quick question I have: for NFPA 211, a couple of the options says to use noncombustible insulation board. I can't seem to find any specific definition for this though (vs. for mineral wool insulation they give a thickness and density requirement). My observation from reading all of the wall protection posts here is that everyone interprets this to mean 1/2" durock? Is that correct?

 

[begreen]

Decided this should just be a new thread...So long time since I posted, but I was finally able to get a Hearthstone Shelburne, and am going to start working on making the protected alcove! I'm really excited about this project!

One (of I'm sure many) quick question I have: for NFPA 211, a couple of the options says to use noncombustible insulation board. I can't seem to find any specific definition for this though (vs. for mineral wool insulation they give a thickness and density requirement). My observation from reading all of the wall protection posts here is that everyone interprets this to mean 1/2" durock? Is that correct?

The verbiage for NFPA is a bit dated. Typically cement board is used if a backer board for tile or brick veneer is desired, but if one wants a simpler wall shield then 24 ga sheet metal will do.

 

[overlandsea]

Yeah, I was actually thinking about doing unventilated...1 inch mineral wool covered with 1/2 inch...apparently durock works. For this option they don't list using sheet metal, though I know it is an option for the ventilated.

 

[begreen]

Yeah, I was actually thinking about doing unventilated...1 inch mineral wool covered with 1/2 inch...apparently durock works. For this option they don't list using sheet metal, though I know it is an option for the ventilated.

That may suffice, depending on the stove's clearance documentation.

 

[overlandsea]

That may suffice, depending on the stove's clearance documentation.

Yes it gives specific reduced clearances for NFPA 211 protection including reduced clearances in alcoves. However, as far as which methods of wall protection, all it says: "You can reduce the clearances to combustibles by using any NFPA approved wall protection system. Please refer to NFPA 211 for specifications and complete details." Based on the "any" this method should work, I think.

 

[kennyp2339]

Steel studs, cement board, and stone veneers using traditional masonry based adhesion (non glues) are your friends here, since this will be non load barring and all cosmetic you have tons of flexibility with making certain cuts to your steel studs to make things more flexible / eye appealing. Just remember that if you don't have the blower option on your stove the closer you build the alcove the more your sacrificing heating beyond since radiant heat will blocked by the alcove. Don't use masonry glues since once exposed to a certain amount of heat that loose there strength in holding power and follow the alcove instructions in the stove manual.

 

[overlandsea]

Steel studs, cement board, and stone veneers using traditional masonry based adhesion (non glues) are your friends here, since this will be non load barring and all cosmetic you have tons of flexibility with making certain cuts to your steel studs to make things more flexible / eye appealing. Just remember that if you don't have the blower option on your stove the closer you build the alcove the more your sacrificing heating beyond since radiant heat will blocked by the alcove. Don't use masonry glues since once exposed to a certain amount of heat that loose there strength in holding power and follow the alcove instructions in the stove manual.

Lots of great tips, thank you so much! I was already planning on using thinset to attach the veneer stone. Is there any kind of glue you recommend for other items? I was thinking to glue the mineral wool boards in place at least to hold while building. Liquid nails says all their stuff in non-flammable once it dries, but not sure if it will hold up well over heat exposure.

 

[begreen]

Yes it gives specific reduced clearances for NFPA 211 protection including reduced clearances in alcoves. However, as far as which methods of wall protection, all it says: "You can reduce the clearances to combustibles by using any NFPA approved wall protection system. Please refer to NFPA 211 for specifications and complete details." Based on the "any" this method should work, I think.

Can you provide a sketch or two that shows the layout and the final clearances you are trying to achieve from the back and sides of the stove?

 

[overlandsea]

Definitely! So going for a 39 inch wide clearance to combustibles for the alcove (which is what the manual lists as the min for NFPA protected surfaces in alcoves), and 3 inches from the rear (it doesn't give a separate rear clearance for alcoves, so I'm just going with the only number they give for rear, which is 3 inches for NFPA protected surfaces), also going for a raised hearth and short height of 18" above the top of the stove (about 48" total...again NFPA protected ceiling). This explains the reason for going with the 1" mineral wool and 1/2" durock protection rather than ventilated. With the ventilated, NFPA wants there the wall shields to go up 36" from the top of the stove to the unprotected top where the ventilation terminates. With the mineral wool/durock combo, there is no unprotected area for the ventilation to terminate at the top. I know these are smaller clearances than most stoves, but that's why I went with the Shelburne...it allows relatively small clearances and they are listed in the manual, not calculated. If I'm not reading something right, though please let me know!



Here's what I have now: The alcove is replacing a corner install ZC factory fireplace. I plan to keep the hearth at current height and do the alcove above it (not as common, I know, but it's so nice to sit next to the fire).



Here's a layout: The pink triangle shows the limits of the existing framing. The gray rectangle is the 39" wide alcove. Obviously, I'll use a noncombustible mantle shelf at the top of the alcove. The stove is a scaled diagram of the Shelburne. The diagram below is approx to scale.

 

[begreen]

Got it, that's helpful. You will be ok as long as strict attention is paid to the specs. What needs clarification before proceeding is what Hearthstone means by NFPA 211 shielding. Generally this is interpreted as the maximum case, which is a ventilated shield. However, if you build the alcove with metal studs then you are gaining the additional space to combustibles for the stud widths, so it might be ok to use the 1" insulation board. A call into Hearthstone support is advisable for verification.

I'm wondering why put in an alcove install as opposed to a straightforward corner install without the alcove sides?

 

[overlandsea]

Got it, that's helpful. You will be ok as long as strict attention is paid to the specs. What needs clarification before proceeding is what Hearthstone means by NFPA 211 shielding. Generally this is interpreted as the maximum case, which is a ventilated shield. However, if you build the alcove with metal studs then you are gaining the additional space to combustibles for the stud widths, so it might be ok to use the 1" insulation board. A call into Hearthstone support is advisable for verification.

I'm wondering why put in an alcove install as opposed to a straightforward corner install without the alcove sides?

Got it, that's helpful. You will be ok as long as strict attention is paid to the specs. What needs clarification before proceeding is what Hearthstone means by NFPA 211 shielding. Generally this is interpreted as the maximum case, which is a ventilated shield. However, if you build the alcove with metal studs then you are gaining the additional space to combustibles for the stud widths, so it might be ok to use the 1" insulation board. A call into Hearthstone support is advisable for verification.

I'm wondering why put in an alcove install as opposed to a straightforward corner install without the alcove sides?

Yes, I emailed them to clarify about a week ago and still haven't heard, so I'll call. The manual says "any" NFPA protection method, and it would be impossible to do a protected ceiling and protected walls with the clearances they give unless you did un-ventilated, so that's why I landed there. As far alcove vs corner install...we went back and forth on it. If something comes up where the alcove doesn't work out, we'll just do the freestanding corner, but we liked the aesthetic of still having a mantle shelf and the angled wall above. Maybe like the look of it 20% more, and considering that this is something we'll live with for 20+ years (love our house/location, hope to never move), it's worth a little extra work if we can make it work.

 

[begreen]

Need more specifics. This is the first time that ceiling clearances have been mentioned or a mantel. It sounds like the plan may be to try to make this look like a stove in a fireplace. If so, great attention needs to be paid to ALL clearances and construction.

 

[overlandsea]

Yes, it may look more like a fireplace, at least in size...Looking at it from the front, the clearance to combustibles would be 39" wide and 48" tall (30" for the stove and 18" clearance). I know that's small compared to most alcoves, but I did buy the Shelburne because it has the smallest published clearances (all with NFPA protection of course) I could find.

The issue I see with ventilated wall protection for their published clearances is that the 1" gap at the top is unprotected from the way I read NFPA. And NFPA doesn't want that unprotected gap at the top within 36." Of course they have a thing about manufacturers can publish specific their own tested numbers. So I think the lesson is that I need to get in touch w/ Hearthstone and get them to clarify.

 

[begreen]

If the alcove is constructed with metal studs and faced with the insulation board then cement board + tile (including the ceiling), so that it is entirely non-combustible, then it may be ok. Watch the rear corner clearances for the stove. That looks like the closest point to combustibles in this case.

 

[overlandsea]

If the alcove is constructed with metal studs and faced with the insulation board then cement board + tile (including the ceiling), so that it is entirely non-combustible, then it may be ok. Watch the rear corner clearances for the stove. That looks like the closest point to combustibles in this case.

Yes exactly what I was thinking. The rear corners, front corners, and front top are all the "hot spots" to be careful of. I'll post what I hear back from Hearthstone.

 

[overlandsea]

Just go off the phone with Jim at Hearthstone and he was super helpful. He said that they want it to be protected using ventilated shielding, not un-ventilated. He clarified that you could have a 39" wide, 48" tall (30" for stove plus 18" above) to combustibles alcove, and there would be the 1" air gap at the top not covered by anything and that was acceptable.

I'm glad to get clarification. I'm happy to build it this way. Perhaps I'll do both the 1" mineral wool/durock directly against combustibles, plus ventilated sheet metal off of that for some extra protection.

 

[begreen]

Thanks for the update. This is consistent with other stove companies' requirements. Hearthstone should change the docs to clarify this requirement.

 

[overlandsea]

I agree, it would be helpful if they were more specific, especially since they went to all the work of specifically listing the protected alcove dimensions. However, at least they were able to still help.

Follow up question: I can artificially make thing smaller if I use entire non combustible protection correct? For example, in the diagram below, the gray box represents the 39" clearance to combustibles. The blue box represents the ventilated wall protection. That would be okay, correct? Goal is not to make it as small as possible, but rather to put some mineral wool insulation in that additional space in between the ventilated wall system and the combustibles.

 

[begreen]

As long as the ventilated wall system is properly ventilating there is no need for the mineral wool, but if you want to add a layer it must not interrupt the flow of air from behind the wall and ceiling shields.

 

[overlandsea]

So as I'm starting to piece this thing together in my garage, I notice having so many transitions in stove pipe in such a short space is going to look busy. Is it possible/acceptable to just use Class A chimney directly from the stove all the way up and skip the stove pipe? I know I've seen pictures of it done, but I can't find any information about how to do it.

 

[begreen]

What chimney pipe and what transistions? A DuraTech system should be pretty clean with a single, short, telescoping pipe length connecting to the stove.

 

[overlandsea]

What chimney pipe and what transistions? A DuraTech system should be pretty clean with a single, short, telescoping pipe length connecting to the stove.

Selkirk DSP...stove, stove adapter, telescoping length (which has a seam), chimney adapter...all in 24 inches.
I mean it can work, I was just wondering if the direct to chimney is allowed?

 

[overlandsea]

Ok so a few more questions that have come up:

1) Can I use just chimney straight up from the stove and skip the stove pipe?

2) What do you recommend for metal studs? I've read that the ones at big box stores aren't super strong...just for interior walls, so maybe try to find 18 gauge metal studs from a lumber yard? Is that necessary? It will be carrying the weight of the chimney. Could slotted angle iron be strong enough? Probably more expensive, but sourcing things is a little more difficult with current lockdowns. Something like this: Zoro angle iron kit

 

[begreen]

Selkirk DSP...stove, stove adapter, telescoping length (which has a seam), chimney adapter...all in 24 inches.
I mean it can work, I was just wondering if the direct to chimney is allowed?

Have you already bought the chimney pipe? There are simpler systems as previously mentioned.

Ok so a few more questions that have come up:

1) Can I use just chimney straight up from the stove and skip the stove pipe?

2) What do you recommend for metal studs? I've read that the ones at big box stores aren't super strong...just for interior walls, so maybe try to find 18 gauge metal studs from a lumber yard? Is that necessary? It will be carrying the weight of the chimney. Could slotted angle iron be strong enough? Probably more expensive, but sourcing things is a little more difficult with current lockdowns. Something like this: Zoro angle iron kit

1) It's been done, not the most attractive and there is a bit of concern about ease of cleaning and the fit + seal at the flue collar.

2) Out of my field. I'm not a carpenter and will defer to those who have worked with metal studs for this kind of work.

 

[overlandsea]

Have you already bought the chimney pipe? There are simpler systems as previously mentioned.

I could return it. I actually went w/ Selkirk DSP because they have the shortest telescoping pipe I could find (12"-18"). Since I'm trying to limit the height above the stove, I thought this would be best. However, now that I have it, I realize 1) there are a lot of horizontal seams, and 2) min height can acheive with this set up is 24" and I'd like to get closer to 18". That's why I thought just go with class A from the stove. There would be no seams in view, and I'm guessing I'm not really saving any money using stovepipe since it's such a short length.

How would you do it?