Blocking off 2nd brick thimble of functional chimney

[poissonn]

Hi all,

First time poster here. I've purchased a house and currently doing a complete tear down and rebuild of the interior and exterior. There is an existing cinder block chimney that has been lined with a stainless steel insert. I plan on using it this winter with the wood stove in the basement. During the tear-down, we found out that there used to be a 2nd stove on the 1st floor connected to the same chimney, before it was lined with stainless. The previous owner only put some fireproof mineral wool in the hole before putting drywall over....I'd like to close off this hole in the proper way with brick and mortar. Here's some pictures of what I need to deal with:

With that being said, I've got a few questions:

1. Should I cut back some of the bricks to create a space for insulation behind the drywall? Currently the bricks (in not so good shape) are flush with the interior of the studs.
2. Can I use regular bricks or they need to be some specific clay type or something?
3. Should I use type N or type S mortar? I've seen both being recommended...

 

[bholler]

Hi all,

First time poster here. I've purchased a house and currently doing a complete tear down and rebuild of the interior and exterior. There is an existing cinder block chimney that has been lined with a stainless steel insert. I plan on using it this winter with the wood stove in the basement. During the tear-down, we found out that there used to be a 2nd stove on the 1st floor connected to the same chimney, before it was lined with stainless. The previous owner only put some fireproof mineral wool in the hole before putting drywall over....I'd like to close off this hole in the proper way with brick and mortar. Here's some pictures of what I need to deal with:

View attachment 283027View attachment 283028View attachment 283029

With that being said, I've got a few questions:

1. Should I cut back some of the bricks to create a space for insulation behind the drywall? Currently the bricks (in not so good shape) are flush with the interior of the studs.
2. Can I use regular bricks or they need to be some specific clay type or something?
3. Should I use type N or type S mortar? I've seen both being recommended...

First thing is to see if the liner is insulated because you clearly don't have the required clearance to combustibles. The right way to fix that is to pull the liner and replace that tee with a coupler. The next best thing would be to cut the tee snout as far back as possible seal it with a stainless cap then insulate and then brick over it. I would say type s or type o

 

[poissonn]

The liner is not insulated. As for clearances, I'll make sure to address those as per the NBC (canadian code). For exterior chimneys such as this one, the clearance should be 12mm between the masonry and any combustible material / framing. That should be fairly easy to accomplish...

As for the right way to fix this that you mention above, when you say that I should replace the tee with a coupler, I'm not sure what you mean. If you take a look at the picture below, the liner goes straight down to the basement. There is no tee. I'm assuming they installed the liner after they got rid of the first floor stove. Is that what you meant?

Thanks!

 

[begreen]

You've inherited a pretty half-baked setup, but not all that untypical. I'd insulate the liner. There may be other unseen hacks and patches. There will be the added benefit of better performance and a cleaner flue as long as dry wood is burned.

 

[bholler]

The liner is not insulated. As for clearances, I'll make sure to address those as per the NBC (canadian code). For exterior chimneys such as this one, the clearance should be 12mm between the masonry and any combustible material / framing. That should be fairly easy to accomplish...

As for the right way to fix this that you mention above, when you say that I should replace the tee with a coupler, I'm not sure what you mean. If you take a look at the picture below, the liner goes straight down to the basement. There is no tee. I'm assuming they installed the liner after they got rid of the first floor stove. Is that what you meant?

View attachment 283031

Thanks!

Ok I thought I saw a tee there. In that case just brick over it. But really the liner should absolutely be insulated. It will greatly improve your performance

 

[poissonn]

Yeah, I'll go the the chimney store near by see if they have something insulated that could fit in that chimney. The current liner is a pretty tight fit, maybe 1/2" all around it. Otherwise I might end up putting the whole chimney down and install a brand new insulated one and box some framing around it with siding

 

[begreen]

Is this an 8"x8" flue in the chimney? If so it would need to be something with an OD <7".

The current liner appears to be rigid. Do you know if it is pre-insulated like DuraLiner? or just single-wall.

 

[poissonn]

It is rigid indeed but when I look through the chimney it looks (and sounds when you knock on it) like a single wall. I'm not at the house tonight but I'll measure it up tomorrow. If it's 8" then hopefully I can fit a 6" insulated in there. I know the pipes to the stove in the basement are 6" double wall, but I don't recall seeing any reducers near the wall.

I'll take a look tomorrow morning and report back. Thanks for the help, really appreciated.

 

[poissonn]

Hi all, so I've removed the stove pipe in the basement. The liner is 7", not insulated. Furthermore, I went to the local chimney store here and I've been informed that cinder blocks (hollow) chimneys are not code compliant, as masonry chimney needs to be made of at least 3in thick material.

So since I'm renovating the whole house including siding and that I plan on staying here for 10+ years, I guess a brand new class A chimney cannot hurt!