vent chimney

[loke211]

Hello Everyone,


I have a question I've been pondering. A little background. Remodeled my house and tore out the old wood burning fireplace and chimney and installed a new wood stove (more of an insert actually). The chimney is all new, constructed of metal studs, high temp insulation between double hardboard walls. Everything within a foot of it is fire resistant. One side of the chimney faces the exterior for entire 15' run up. Inside the chimney is a stainless liner connected to the stove and cap on top of chimney. Inside dimensions of chimney are 9x10 and the liner is 6" round.

Now to the question. When burning the stove I notice that the chimney gets quite a bit warm from the outside, especially towards the top, from the stainless liner which is not insulated. Is there a need to release all that hot air via some sort of vent that can be opened only when burning? Or the temperatures inside the chimney "dead space" (between block off on top of stove and chimney cap) don't reach high enough for me to worry about this? I was thinking of pouring insulation mix down the chimney but there seems to be an argument on this subject.

 

[bholler]

Hello Everyone,



I have a question I've been pondering. A little background. Remodeled my house and tore out the old wood burning fireplace and chimney and installed a new wood stove (more of an insert actually). The chimney is all new, constructed of metal studs, high temp insulation between double hardboard walls. Everything within a foot of it is fire resistant. One side of the chimney faces the exterior for entire 15' run up. Inside the chimney is a stainless liner connected to the stove and cap on top of chimney. Inside dimensions of chimney are 9x10 and the liner is 6" round.

Now to the question. When burning the stove I notice that the chimney gets quite a bit warm from the outside, especially towards the top, from the stainless liner which is not insulated. Is there a need to release all that hot air via some sort of vent that can be opened only when burning? Or the temperatures inside the chimney "dead space" (between block off on top of stove and chimney cap) don't reach high enough for me to worry about this? I was thinking of pouring insulation mix down the chimney but there seems to be an argument on this subject.

Are you telling us you have an insert and single wall uninsulated liner inside a steel stud structure?

 

[loke211]

Are you telling us you have an insert and single wall uninsulated liner inside a steel stud structure?

Yes. The chimney structure is insulated with fire resistant insulation between two layers of hard board, like standard 2x4 wall framing and sheetrock/insulation/sheathing. The insert "box" is done the same way. When installing the liner I was told the liner does not need to be insulated since the chimney is.

 

[bholler]

Yes. The chimney structure is insulated with fire resistant insulation between two layers of hard board, like standard 2x4 wall framing and sheetrock/insulation/sheathing. The insert "box" is done the same way. When installing the liner I was told the liner does not need to be insulated since the chimney is.

Who told you that? You don't have a chimney you have a framed and insulated structure. This does not meet any code at all anywhere in the USA and is potentially extremely dangerous.

 

[bholler]

What insert do you have?

 

[loke211]

What insert do you have?

Who told you that? You don't have a chimney you have a framed and insulated structure. This does not meet any code at all anywhere in the USA and is potentially extremely dangerous.

correct, it is not a chimney but more of a chase for the liner. New was a better option then lining the old crumbling chimney and more cost effective than building an actual chimney. The structure is 100% fireproof materials so I don’t see an issue or danger. The stove is Hearthstone Clydesdale.

 

[bholler]

Just because you don't see the danger doesn't mean it isn't there.

That insert is designed to be installed only in a code compliant wood burning fireplace. You don't have that.

Your liner is only meant to be installed in a masonry chimney made with 4" nominal solid masonry units. You don't have that.

Do you have absolutely complete coverage with that insulation? What about heat transfer through the metal studs? What happens if the insulation settles? Is the insulation equivalent to the required 10" of solid masonry in the firebox? What is the hearth construction?

Please stop using this setup immediately it is very very unsafe!!

 

[Shrewboy]

correct, it is not a chimney but more of a chase for the liner. New was a better option then lining the old crumbling chimney and more cost effective than building an actual chimney. The structure is 100% fireproof materials so I don’t see an issue or danger. The stove is Hearthstone Clydesdale.

heed the warning and advice of bholler! he does this stuff for a living

 

[loke211]

Just because you don't see the danger doesn't mean it isn't there.

That insert is designed to be installed only in a code compliant wood burning fireplace. You don't have that.

Your liner is only meant to be installed in a masonry chimney made with 4" nominal solid masonry units. You don't have that.

Do you have absolutely complete coverage with that insulation? What about heat transfer through the metal studs? What happens if the insulation settles? Is the insulation equivalent to the required 10" of solid masonry in the firebox? What is the hearth construction?

Please stop using this setup immediately it is very very unsafe!!

You bring up good points, but for what it’s worth the structure has been checked out by a building inspector both at framing and final with no concerns.

I’d also like to point out that the insert is not set flush against the finished tiled wall. I did not use the decorative face plate so there is a 1” gap around the unit to allow hot air from the box into the house.

Now back to my question. Would it be beneficial to fill the chase with insulation (there is a block off plate at the top of the box).

PS: this fireplace is not primary heat for the home. It’s more of a novely used a few times a month in the wintertime.

 

[loke211]

heed the warning and advice of bholler! he does this stuff for a living

I do appreciate and value professional advice.

 

[bholler]

You bring up good points, but for what it’s worth the structure has been checked out by a building inspector both at framing and final with no concerns.

I’d also like to point out that the insert is not set flush against the finished tiled wall. I did not use the decorative face plate so there is a 1” gap around the unit to allow hot air from the box into the house.

Now back to my question. Would it be beneficial to fill the chase with insulation (there is a block off plate at the top of the box).

PS: this fireplace is not primary heat for the home. It’s more of a novely used a few times a month in the wintertime.

You do realize the inspector bears no liability what so ever for things that were missed. If you did this all liability is on you and you alone. Did he look at the instructions for the insert and liner?

No it will not be benificial to pour insulation into your chase. Because no matter what you do this setup is not safe at all.

 

[loke211]

You do realize the inspector bears no liability what so ever for things that were missed. If you did this all liability is on you and you alone. Did he look at the instructions for the insert and liner?

No it will not be benificial to pour insulation into your chase. Because no matter what you do this setup is not safe at all.

I appreciate your replies and insight. Not here to argue. However I disagree that it’s unsafe. All materials that were used and everything within 1’ from there is non combustible. I do see your point on the parameters of stove and liner installation and will seek further advice locally. Thank you.

 

[MongoMongoson]

Yes. The chimney structure is insulated with fire resistant insulation between two layers of hard board, like standard 2x4 wall framing and sheetrock/insulation/sheathing. The insert "box" is done the same way. When installing the liner I was told the liner does not need to be insulated since the chimney is.

Just so you understand, sheetrock is not non-combustible. It has a paper face on it. I know it is something of a special material, because of the gypsum in it. The gypsum will help put the flaming paper out because it gives off CO2 when it gets hot... But yeah, you can certainly still have flaming paper.

The person who said your liner didn't need to be insulated... are you sure they understood that you don't really have a chimney? If you told me your chimney was insulated, I might agree that you don't need an insulated liner.

But if I looked at what you describe here, I'd know you are running an uninsulated liner up an insulated chase that has no chimney in it. I'd tell you that you just can't do that.

I think seeking advice locally from a certified chimney sweep is the way to go. In my limited experience with building inspectors.... They know a lot less about chimneys and wood stoves than I do so I don't think you can count on an inspector's seal of approval here.

 

[bholler]

I appreciate your replies and insight. Not here to argue. However I disagree that it’s unsafe. All materials that were used and everything within 1’ from there is non combustible. I do see your point on the parameters of stove and liner installation and will seek further advice locally. Thank you.

There are products made to be installed in a chase like you have. But the products you chose to use are not correct for that application at all.

 

[loke211]

Just so you understand, sheetrock is not non-combustible. It has a paper face on it. I know it is something of a special material, because of the gypsum in it. The gypsum will help put the flaming paper out because it gives off CO2 when it gets hot... But yeah, you can certainly still have flaming paper.

The person who said your liner didn't need to be insulated... are you sure they understood that you don't really have a chimney? If you told me your chimney was insulated, I might agree that you don't need an insulated liner.

But if I looked at what you describe here, I'd know you are running an uninsulated liner up an insulated chase that has no chimney in it. I'd tell you that you just can't do that.

I think seeking advice locally from a certified chimney sweep is the way to go. In my limited experience with building inspectors.... They know a lot less about chimneys and wood stoves than I do so I don't think you can count on an inspector's seal of approval here.

The structure is covered in cement board not Sheetrock. Nearest Sheetrock and wood framing is 2’ away. Past 2 layers of hardie board, with fireproof insulation in between

 

[loke211]

There are products made to be installed in a chase like you have. But the products you chose to use are not correct for that application at all.

Please elaborate. Thank you

 

[EbS-P]

(broken link removed to https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/usg-durock-cement-board-with-edgeguard-submittal-en-CB399EG.pdf)

Page 3 #13.

Max temp is 200dF.

 

[loke211]

(broken link removed to https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/usg-durock-cement-board-with-edgeguard-submittal-en-CB399EG.pdf)

Page 3 #13.

Max temp is 200dF.

I used Hardiebacker fiber cement board like this:

https://www.lowes.com/pd/James-Hardie-0-42-in-x-36-in-x-60-in-HardieBacker-Fiber-Cement-Backer-Board/3067737

 

[bholler]

Please elaborate. Thank you

You should have used a prefab fireplace and chimney