Flex Chimney Liner Install for 9x13 Terra Cotta Chimney

[mdmallard]

Hi All,

We moved into our house two years ago and I'm in the process of replacing our 35+ year old Blaze King stove with a Blaze King Sirocco 30 or Princess stove. I went up on the roof last week and it looks like I'll need 20-25 feet of liner. My question is with the inside measurements of my terra cotta liner being 7.25" x 11.25" how hard will it be to install a 6" diameter flex liner with the 1/2" insulation blanket and the wire mesh? It seems like it will be a very tight fit. Would you guys recommend a pulling cone to help get it down the chimney?

 

[bholler]

It wont work you will either need to remove the old clay or go with an ovalized liner.

 

[Dr. McMaster]

Hey mdmallard!

Bholler is correct, you likely won’t be able to fit a 6” liner with 1/2" insulation blanket and the wire mesh. I have a very similar size clay flue, and remember trying to work out if I could make a standard 6” liner work, and even with going with only the ½” insulation the numbers just don’t work out. The 6” liner has a larger OD than 6” (6.25 or larger, if I remember correctly), and when you install the insulation you are supposed to overlap it a bit to make sure you have coverage. Even if you don’t, you are right at the 7.25” at best. Factor in the likelihood of occasional jogs or slightly offset clay liners, especially over 20+ feet, and you’re asking for a snag. I know in my chimney there was one clay flue section that was laid offset by a good half inch.

So, like Bholler said, you can rent the tools to break out the existing clay liner (which consists of extension bars with an offset weight that you spin with a drill to crack the liner), which I hear sometimes goes well and easy, and sometimes ends up being a nightmare. Or you can run an ovalized liner. You then buy an oval to 6” round adapter. This is what I ended up doing. I believe my liner is something like 4.5”x8”, or something close to that. I found a number of charts that recommend the appropriate oval size for a given round size (given the slight loss of draft efficiency in an oval vs round liner).

I know some people have gotten around this by using a 5.5” liner instead. With a long run like you have, where you should be able to establish a good draft (so long as you don’t have other environmental issues affecting your local install), I have read about 2 or 3 people that have done this successfully and said they have no issues with how their stoves run. A round liner is cheaper than an ovalized liner as well. I can’t guarantee this will work well for you, but it is something to consider. Maybe try contacting Blaze King and running your particular install condition by them and see how they feel about a 5.5” liner. I know Rockford Chimney Supply sells smooth inner wall flexible liners, which are actually a smooth liner inside a standard corrugated liner. According to them, “Its smooth interior design allows for more airflow, adding back the 20% drag factor that's lost in traditional corrugated liners”. This should technically make up for the loss of draft area of going from a 6” liner to a 5.5” liner. Something to think about.

I think the most important thing is that you find a solution that allows you to insulate the liner. Don’t skimp on that bit (unless the chimney runs up the inside of the house, and is not exposed like many chimneys are, though even in this case it is still valuable to insulate). And the pulling cone is defiantly worth it, regardless of what you go with.

Not an expert here, just my thoughts and observations from reading through this forum and researching my challenging install a bunch over the past two years.

 

[bholler]

I know Rockford Chimney Supply sells smooth inner wall flexible liners, which are actually a smooth liner inside a standard corrugated liner. According to them, “Its smooth interior design allows for more airflow, adding back the 20% drag factor that's lost in traditional corrugated liners”. This should technically make up for the loss of draft area of going from a 6” liner to a 5.5” liner. Something to think about.

Do not buy that type of liner it is by far the least durable liner type on the market. If you want smooth wall go with heavy flex or mid weight flex. Both are smooth wall and are also slightly smaller outside diameter.

Otherwise your comments are right on.

 

[Dr. McMaster]

Good to know bholler! With regards to the heavy flex / mid weight flex, who actually manufacturers that? Is it something that a consumer can buy direct, or is it only sold through installers?

 

[bholler]

Good to know bholler! With regards to the heavy flex / mid weight flex, who actually manufacturers that? Is it something that a consumer can buy direct, or is it only sold through installers?

most liner manufacturers have heavy flex the mid weight stuff is newer and not everyone has it yet but it is a good compromise. It is more durable than light wall it is smooth wall and it costs less than heavy wall. We use it on some new wood stove installs. But for older stoves or stoves that will be the primary heat source we still use heavy wall. Also the offset breakers are no longer used much we all use breakers that have weights on chains now run with the same rods. They are much easier to run and have less potential for damage to the chimney. But we still have the offset ones for liners that are a pain to get out.

 

[mdmallard]

most liner manufacturers have heavy flex the mid weight stuff is newer and not everyone has it yet but it is a good compromise. It is more durable than light wall it is smooth wall and it costs less than heavy wall. We use it on some new wood stove installs. But for older stoves or stoves that will be the primary heat source we still use heavy wall. Also the offset breakers are no longer used much we all use breakers that have weights on chains now run with the same rods. They are much easier to run and have less potential for damage to the chimney. But we still have the offset ones for liners that are a pain to get out.

Thanks everyone for all the information. I am going to reach out to Blaze King to see if they can offer me any suggestions as well. It looks like my easiest path will be to get an oval liner (5'x7"?) and go that route.

 

[RichW_SC]

I'm in the same boat... What about going with a 6" round and using vermiculite insulation?

 

[bholler]

I'm in the same boat... What about going with a 6" round and using vermiculite insulation?

be aware that you will not have enough insulation to meet the zero clearance requirement so if you dont have proper clearance you could have a safety issue