i Want to put a wood stove in my basement and reuse the old oil fired furnace chimney, when the previous owner put an addition on the house he capped off the chimney at the roof line. The Harmon wood stove requires a 6 inch flue which is the same size as the clay liner inside the chimney, however it looks not in good condition lots of cracks and looks like some has worn away., This being said I don’t trust it , worried about chimney fire and possibly leaking smoke in house, so I took out the old clay liner , good thing too, in some spots it was less than 1/8 inch thick, This left the chimney block and an approx 9 inch opening , I am considering installing a class a double wall chimney in the existing masonry the run and extending the masonry above the roof line using the 10-3-2 rule The run is will be about 25 feet and straight up . Is this doable, and how is it supported inside the masonry, Any advice u can give would be great, Thanks
Repurposing old decommissioned chimney
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It is not doable and won't meet code class A chimney isn't rated for that. Run an insulated liner through the chimney then transition to class A at the top
I wonder why ? Isn’t an insulated liner basically the same thing ? A rigid flue pipe, with a installed liner ,
No not the same at all. A liner is designed and tested to go into a chimney. Class A is a chimney. Not to mention with class A you would have no way to hook up at the bottom.
And with class A you would be paying for a lot that simply isn't needed inside a masonry chimney
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They screw togethe
the class a screws together don they, And there is enough room to cut a pocket in the basement wall it’s not load bearing, It to me seems that the class a is a safer option, more work but safer.
How is it safer? Regardless it doesn't meet code because class A chimney is not specified to be used inside a masonry chimney. It needs to be supported at the given intervals(usually every 8'.
2” clearance to combustibles. I also had a old acquaintance of mine that had his chimney reclined , he did all the correct maintenance, chimney caught fire and burned his house down.
Yes and an insulated liner inside a masonry chimney is zero clearance.
Was the chimney lined properly? If your that worried about it double wrap the liner and it will have the same amount of insulation be cheaper and meet code
If your really set on using class A there isn't a safety issue as long as you can figure out how to support it. But all of its listing will be voided. Warranty gone and you won't meet code
I know you can’t speak to why it would void warranty? Aren’t most chimney pipe supported from bottom? Wouldn’t that exceed code?
It would void the warranty because it is being installed in a way that doesn't conform to the listing.
And most chimneys are supported from the bottom then every 8' from there
Was the liner insulated? It's very common for installers to skip that step and a mistake. A bad chimney fire can still catch the roof on fire, even with a class A chimney if hot embers and tar globs fall on the roof and the fire dept. is slow to get there.
Did not know that , about the 8’ rule in the chimney, . well how does the liner, I’m looking at rigid ,get supported.
It gets hung from the top. But I really prefer heavy wall flex liner over rigid. Rigid has allot of fasteners holding it together that can eventually fail. Rigid it still a good liner I just don't see the benefits being worth the added hassle.
And there is no rule about how often a class A chimney needs to be supported inside a chimney because it's not designed to be installed there.
That’s what
thats what worries me about the fasteners, ok guess it’s back to the drawing board.
If 3 stainless pop rivets are used per joint, it's going to stand up well. It's when steel or aluminum rivets are used that failures are more common. I pulled a 10 yr old rigid stainless liner after 12 yrs service and it was still in excellent condition. And that was after a major earthquake. That said, a heavy-duty flex liner will alleviate this worry if it is a concern.
Begreen is right if the proper rivets are used it won't be a concern for atleast 20 years probably more. Screws not as long
I'm not sure where the "it needs to be supported every 8'" comes from since Selkirk states: "Maximum length of chimney which can be suspended below is 20 feet. Maximum total chimney length is 30 feet." Personally, i'd have no issue installing a class A inside a masonry flue, i honestly cant see any issue with that install. As long as it'd fit inside, it seems to meet the basic requirements of being over 2" to combustibles and there would obviously be some air flow around it so why not? Yes, supporting it would be a little tricky but their roof support could be tied into the top of the flue with some modifications. You may need custom brackets made up but it's doable.
But it will cost more for no reason. Be a real pita to install. And won't meet code because it isn't installed to manufacturer's instructions. As far as the 8' thing I said most require that. I won't use Selkirk so I don't know their requirements. But there is no way I would trust their twist lock and chinsy lock bands to suspend 20' of chimney
Agreed. Doing this with class A would be expensive overkill. If rigid is desired, DuraLiner makes an insulated liner system for this purpose. Member Hogwildz has a Duraliner system that's been in for about 15(?) yrs now.
Well, i've trusted those "chinsy" lock bands for about 15 years now without issue. I've also known a lot of people who havent had issues with those bands but have seen first hand the result of chimney fires in houses without class A systems. The sections of Class A are not heavy at all so supporting them is not a big deal. Considering the pricing on GOOD liners, the price between Class A and a liner might be about the same.
The difference is that a heavy-duty flex liner goes in faster, is as durable, and has a lot fewer joints. bholler can give a cost comparison.
The price of a high quality prefab chimney right now is roughy 2.5x the price of an insulated heavy wall chimney. And yes a masonry chimney with an insulated stainless liner is a class A chimney as well and actually has lower clearances than a prefab stainless class a.
BTW i.have absolutely no issues with prefab chimneys I install allot of them. They are a very good option they just aren't meant to be used insde a masonry chimney. And Selkirk chimneys are perfectly fine when installed as intended I just don't like their locking mechanism I have had to many of them come apart when cleaning
A lot of extra joints captive in an enclosed brick jacket is a valid concern.
Nevins MHP
New Member
You can install a Class A chimney in a masonry chase. Once you put class A in the masonry hole, the masonry ceases to be the chimney. The 8' rule is about maintaining clearances with most brands that require something like that. The block is noncombustible and keeps the chimney pipe at least 2" from combustibles. The only reason not to use class A is weight and cost. Weight is a factor because you must support the pipe as you lower it and assemble additional sections. Attaching Class A pipe to a Class A tee is also tricky. If you drop the pipe, the bottom pipe will be garbage. The same goes for the tee of the pipe falls a few feet and hits it.
Duravent Duraliner is available as a double-wall rigid pipe, so no insulation needs to be added. They also make parts to connect to an anchor plate on top and extend the chimney with class A. You will have a listed installation since all the parts are designed to be used that way together. You must add braces if the chimney is more than 5' above the anchor plate.
For an experienced chimney tech, flex is easier. If you don't have much experience, the DuraLiner may be easier because you don't have to support all the weight of the liner while on the ladder and get it to feed into the chimney. Get an extra support band for the liner. Put one on the top of the first two sections. The tee has a removable snout so that you can put the tee on the bottom of the first liner. After the second section is connected, lower them down and let the support band hold both pipes while you attach the first band to the next piece. Repeat until you're at the right height for the tee. Adjust the support band at the correct height and connect the removable snout to the tee.
If you add class A, there will be some additional steps to attach the adaptor to the liner and install the anchor plate. The kit comes with instructions, but you should get the help of a professional in selecting the correct components.
Duravent Duraliner is available as a double-wall rigid pipe, so no insulation needs to be added. They also make parts to connect to an anchor plate on top and extend the chimney with class A. You will have a listed installation since all the parts are designed to be used that way together. You must add braces if the chimney is more than 5' above the anchor plate.
For an experienced chimney tech, flex is easier. If you don't have much experience, the DuraLiner may be easier because you don't have to support all the weight of the liner while on the ladder and get it to feed into the chimney. Get an extra support band for the liner. Put one on the top of the first two sections. The tee has a removable snout so that you can put the tee on the bottom of the first liner. After the second section is connected, lower them down and let the support band hold both pipes while you attach the first band to the next piece. Repeat until you're at the right height for the tee. Adjust the support band at the correct height and connect the removable snout to the tee.
If you add class A, there will be some additional steps to attach the adaptor to the liner and install the anchor plate. The kit comes with instructions, but you should get the help of a professional in selecting the correct components.
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