Alcove Design for Wood Stove in ICF House - Feedback?

[ronsomething]

First time poster...my apologies in advance for the long post, but I've read much on the subject and want to get comfortable with my proposed alcove design...and get other feedback from more knowledgeable Hearth members. Hopefully, others will learn from this as well.

Wood Stove: 2021 Lopi Evergreen stove with legs (not the pedestal), fan and OAK. Placing in an alcove is permitted by mfr. I want the alcove bc I like it, and think I can make it work effectively to heat the house. I am hopeful that the stove will be the primary heat source in the winter; will supplement with propone furnace, as needed.
See attached pics to visualize what I will try to explain below.
New house with exterior walls built with ICF (insulated concrete forms), 6" concrete sandwiched between 2 1/2" of eps foam on each side.
Proposed alcove is to be built in great room with 9 foot ceilings. Alcove is framed with wood 2x4s but I can reframe it with steel studs, if needed.
RO Dimensions: 66 inches tall, 72 inches wide, and 27 inches deep. About half of the stove will sit inside the alcove and half outside. One of the attached pics shows placement.
According to Lopi owner's manual, if the ceiling of the alcove is less than 84", then the alcove requirements must be followed. I want to make it a non-combustible alcove which requires 3.5 inches of non-combustible material and 1" air gap.
My plan design is as follows: Line the interior of the alcove with 1/2 inch Durock fastened to the wood studs. This would run from floor all the way up to 9' ceiling height. I would also attach Durock as the substrate for alcove ceiling (66" high). Then 1 inch air gap created with copper pipe or ceramic spacers. Then 2 inches of qualifying non-combustible material (not sure what this will be yet, but open to ideas...(more layers of Durock, some kind of mortar, etc...but weight may be an issue see below). Then the stone veneer 1.25 inches limestone rock plus mortar (2 inches combined) for a total of 3.5 inches thick. The rock on the interior of the alcove will go just above the opening or ceiling of the alcove, 66 inches (not all the way up to the 9 foot ceiling). This is to save on weight and cost. To be clear the stone veneer will be the surface closest to the wood stove. This stone veneer will also be set on the front of the alcove facing the great room. A non-combustible mantle will be attached above the alcove opening, about 6' from the floor. The stone veneer will continue up to the 9' foot ceiling above the mantle with sufficient room for an air vent for heat to escape. And there will also be stone on each side of the opening facing the room. The ceiling of the alcove will slope upward from the back wall toward the front to allow hot air to escape more easily. On either side of the alcove will be built-in window seats, see the pics, and will be regular drywall with a vent on each side to further allow heat to escape. The stove also has a blower and there is a ceiling fan in the room to move the warm air around. Under the stove will be ember protection: sheet metal under tile or slate which is all that is required by the mfr. for this stove. R-value is not needed. It will extend at least 16 inches in front of the stove. I will run regular stove pipe up to the alcove ceiling (66') then convert to chimney pipe to mitigate heat b/c the surrounding walls in this space (including the ICF foam wall) will only be covered with Durock (no stone in this space). Again, this is to save on the weight and the cost. The chimney pipe will be rated for 2" clearance to combustibles.
I would like some feedback on this issue specifically.

With this design, all the clearance requirements are met (even after taking into account the 3.5 inch thick walls), i.e. there is sufficient clearance between the stove/pipe and the non-combustible stone surface closest to the stove (which is what tech support told me was required).

I've spoken to technical support at Lopi (Travis Industries) and they gave me helpful info. As near as I can tell, this design complies with the written instructions, as well as the verbal discussion we had. But I would like to get feedback from the pros in this forum.

I am having my engineer look at whether the floor needs to be supported. Altogether the finished alcove, wood stove, mantle, and three average-sized people warming themselves will be about 5,000 lbs. There is a basement under this room, but it's finished. Adding columns and beam supports will be destructive and a pain, but I'll do what I have to do.

Any thoughts, feedback, comments on this design? Safety is foremost on my mind! If weight is an issue, I will re-frame the alcove with steel studs, in which case, as I understand, I won't need the 3.5 inch thick alcove walls. The rock veneer embedded in mortar (about 2" thick) should suffice. Do I understand that correctly? The back wall is an ICF foam wall. It's sorta the wildcard here. I plan to cover it as described above with the 3.5' of non-combustible material regardless.

In terms of the heat, will the limestone veneer be ok for this application (1.25" thick)? Or will it be too hot in the alcove? A caution was raised in a couple articles I read (not on this site), so I thought I better get some feed back on this issue, too.

What are your thoughts?
Thanks in advance for all your help. I appreciate it tons.

 

[DBoon]

Welcome to the forum, ronsomething.

You've obviously thought this through really well. It's a little much to absorb all the details without a drawing describing the construction - that might help others comment on the construction. I won't profess to be the expert on alcove construction for a woodstove.

I did own a Lopi Answer that I put in a fireplace opening. It was double-jacketed and had a blower. The front was flush with the fireplace opening. It worked pretty well - the fireplace/alcove didn't get too hot due to the double-jacketing of the stove, and the blower moved the air into the room really well. I think your install will work to get good heat into your room, but I don't want to comment on the alcove construction specifically - others can offer better advice.

In regards to the installation, I built something similar for my new house. You can see photos of that here https://www.hearth.com/talk/threads/new-woodstock-keystone-install.196636/
The alcove for this installation originally started as a fireplace that would hold a woodstove. I turned it into just a basic masonry alcove that is not designed for an installation as you show (I filed a notice with the building department to this effect, and also put a plaque on the back of the alcove to this effect), but it works fine with the Keystone forward from the opening.

I've attached an image of the chimney pipe detail for my recent install. I'd recommend double-wall insulated chimney pipe and a blockoff plate, if you aren't already planning on that. Also, Lopi stoves (in my experience) are pretty easy breathers and can get pretty hot with a tall chimney (27' in my case, with a nice, smooth, insulated pipe). I ran a Lopi 1750 in this installation for a while and it would get pretty hot on the stovetop (650-700 degrees - safe for the stove, but a little above my threshold for what I'd like to have). I used a pipe-damper and that didn't help too much. Just be aware. Better to overdesign the alcove than underdesign it.

 

[ronsomething]

DBoon, thank you for your warm welcome and reply. I had no idea wood stoves could be so complicated 😀.

The alcove in the link you posted is similar looking to what I am trying to accomplish, but in my case the alcove will be a little bigger.
What is the construction of your alcove? How many inches thick is the rock on the interior? I don't understand what you mean about the plaque you attached??
Thanks again.

 

[begreen]

In general terms, why put the freestanding stove in an alcove in new construction if the goal is 24/7 heating? The more the stove sits in the room, the better natural convection will work in the room. The example shown is even worse because it creates a heat pocket above the stove that will not be cooled with natural convection unless there is a vent grille near the top of the cavity.

The wood framing on the front does not honor the clearance requirements for the Evergreen. It should be metal framed with non-combustible cladding or it should be open to the ceiling with no front face. Stone/brick/cement is not required on the interior sides unless one is designing to the much closer non-combustible clearance dimensions. In the example provided, it looks like the combustible clearances are exceeded. If so, no need for shielding. If the ceiling is dropped to the 66" height, then it also should be metal framed and the chimney support would go there. Stovepipe can not go through a wall or ceiling.

 

[cahaak]

I would echo the above comments. Leave the stove out in the room with a nice tiled, stone...wall behind it. It will look better and heat much better.

 

[Rickb]

So.. I did an alcove for my new stove... However I framed all the back all with metal studs and insulated with rockwool. I then actually used 4" stone on the face built up from the concrete floor for support. I also put a blockoff plate in 6 inches down from the ceiling. And I vented above that intop the rafters just so there os no build up of heat. I am not sure I would use wood framing for a alcove on the stove. I know after a day or 2 of running my stove the stone around my stove is very warm. Not burning hot or anything but a nice hot that continues to warm the room after the stove is out.

Plus I wanted to make sure there was no chance of anything getting too hot so there is nothing combustable within 8 foot of the stove other then the carpet but its like 32 inches from the stove door.

 

[ronsomething]

In general terms, why put the freestanding stove in an alcove in new construction if the goal is 24/7 heating? The more the stove sits in the room, the better natural convection will work in the room. The example shown is even worse because it creates a heat pocket above the stove that will not be cooled with natural convection unless there is a vent grille near the top of the cavity.

The wood framing on the front does not honor the clearance requirements for the Evergreen. It should be metal framed with non-combustible cladding or it should be open to the ceiling with no front face. Stone/brick/cement is not required on the interior sides unless one is designing to the much closer non-combustible clearance dimensions. In the example provided, it looks like the combustible clearances are exceeded. If so, no need for shielding. If the ceiling is dropped to the 66" height, then it also should be metal framed and the chimney support would go there. Stovepipe can not go through a wall or ceiling.

Thank you for those comments. I appreciate the feedback very much. You've given me some things to think about.

There are aesthetic reasons for doing the alcove...that's a foregone conclusion. The goal at this point is to make it work as best as possible. I understand the heat trap issue above the stove. Other than a grill to ventilate that space, are there other things that can be done to get that trapped heat out into the room, e.g. fan or blower mounted up there?? What if I put multiple layers of rockwool insulation??

I like the idea to use steel framing for the alcove ceiling. And it's good to know that the sides don't need that 3.5 inches of brick/stone. That will save on weight. Thanks.

When begreen says the front wall doesn't honor the alcove requirements, I'm guessing you are referring to the clearance bt the stove pipe and the front wall. Yes, that's close. So I was planning on using a double walled offset (chimney pipe) for clearance purposes. My reading of the material is that the requirements of the mfr of the chimney pipe would govern (2"). With the offset, the clearance would be about 3 inches from the 3.5 inches of cladding.
Is this what you're referring to, or is there a different clearance issue that you're seeing? I appreciate the feedback.

Rickb, what is a block off plate?
I like the idea of metal framing all the way around just for a margin of safety. I will have to strongly consider that.

FWIW, after posting initially I came across a product called aircrete - cement mixed with a foaming agent. You can find commercially available panels/blocks, etc or with minimal equipment make your own panels and blocks. The fireproof properties are amazing. The Airkrete brand (with a K) has a video demonstrating this.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

On one side of the airkrete wall was a 1100 degree fire. On the other side, the temperature of the wall was only 120!! It also has structural properties...people build houses with it.

This might be a good product for between the stone veneer and combustible framing, as well as the ceiling of the alcove. What do you think?

Again, I appreciate your feedback and your time very much.

 

[FPX Dude]

I like the open it up idea too. Or, if set on the alcove then not make that pocket and have it open all the way to the ceiling.

 

[DBoon]

What is the construction of your alcove? How many inches thick is the rock on the interior? I don't understand what you mean about the plaque you attached

The interior masonry is 8" concrete masonry units covered with a decorative tile that looks like a firebrick.

The initial plan was to put a stove in the alcove (a Lopi Rockport), much like you are proposing with your Evergreen, with the alcove meeting all requirements for a fireplace in terms of masonry clearances to combustibles and what not. The alcove that would have accommodated that installation would also not have had the horizontal masonry (above the woodstove), but that could have been added later (by a different owner). But I soured on needing a blower for the stove as I had grown tired of blower noise in a previous installation, and it's not as efficient an installation to put the stove in an alcove.

Therefore, I made a late construction decision to change the alcove from something that could be retrofitted to be a fireplace someday to just something that would contain a little bit of the back of the woodstove (Woodstock Keystone). This allowed me to forego the normal clearance requirements for masonry to wood framing and seal the house up a lot tighter (I achieved 1.2 ACH50 on an airtightness test before fixing some leaks, and I am sure I am better than 1 ACH50 now). Because I lack clearances between masonry and framing, I put a plaque in the back of the alcove that says "this alcove has not been designed to be used as a fireplace".

The Keystone sits 10" from the front of the hearth and it radiates quite nicely into the room. The heat-generating portions of the stove are not in the alcove area, and the air in that alcove stays at basically room temperature when the stove is burning.

I'm very happy with the decision I made to move the stove out from the alcove. I wanted something that more resembled a traditional Arts & Crafts style fireplace with a woodstove positioned in it, and this installation gave that to me. By sitting the stove in front a bit, I get better efficiency and no blower noise.

 

[Rickb]

If you dont want or like the idea of full brick why not use metal 2x4's with rockwool and concrete board then thin brick? Its like 1/2 inch. Then there is nothing combustible and your good. I have thin brick inside my alcove that looks like a fireplace. Again the front is 4 inch stone. And a block off plate is ussually used in a fireplace just above the insert to help keep the warm air inside and not up the chimney.

 

[TomMcDonald]

If you dont want or like the idea of full brick why not use metal 2x4's with rockwool and concrete board then thin brick? Its like 1/2 inch. Then there is nothing combustible and your good. I have thin brick inside my alcove that looks like a fireplace. Again the front is 4 inch stone. And a block off plate is ussually used in a fireplace just above the insert to help keep the warm air inside and not up the chimney.

Good idea. Those are called brick slips here but not sure what they are in USA

 

[Newbie78]

I'm with the "why are you doing that alcove thing" crowd.

It will definately heat better and, in several opinions here, look better without being stuffed into an unnecessary alcove, which creates heat retention problems for no reason, in some peoples minds..

anyhoo, good luck with the install..

 

[ronsomething]

In general terms, why put the freestanding stove in an alcove in new construction if the goal is 24/7 heating? The more the stove sits in the room, the better natural convection will work in the room. The example shown is even worse because it creates a heat pocket above the stove that will not be cooled with natural convection unless there is a vent grille near the top of the cavity.

The wood framing on the front does not honor the clearance requirements for the Evergreen. It should be metal framed with non-combustible cladding or it should be open to the ceiling with no front face. Stone/brick/cement is not required on the interior sides unless one is designing to the much closer non-combustible clearance dimensions. In the example provided, it looks like the combustible clearances are exceeded. If so, no need for shielding. If the ceiling is dropped to the 66" height, then it also should be metal framed and the chimney support would go there. Stovepipe can not go through a wall or ceiling.

@begreen...you said "The wood framing on the front does not honor the clearance requirements for the Evergreen."
Based on the published evergreen literature, it appears it does, even with the wood framing, assuming there is 1 inch air gap and 3.5 inches of mon-combustible material.
Am I missing something? What are you seeing that violates the requirements? I want to make sure this is safe. Thank you.

 

[begreen]

My concerns are with the practical construction. The clearance exceptions are for the vertical surfaces. Lopi provides specific guidance for this case. The bottom (lintel) plate of the front opening is the exception. How will this be constructed so as to provide the same protection and free airflow as provided for the front and behind? How will covering the bottom avoid blocking the required 1" opening on the front and rear surfaces? Will it be strong enough to carry the weight?

All of these issues are resolved by using metal studding on the front. With metal studs, there is no need to clad the backside. This is why the suggestion is to make the front entirely non-combustible. That solves multiple issues.
The design proposed is not covered in Lopi's docs. Stove manuals typically expect an open front alcove. Submit plan drawings to Lopi for the final word. If they sign off and approve them, then you are good to go.