Rigid vs flex liners

[Watchguy]

We are going to be lining our factory chimney to downsize it a little (from 8" to 6"). I'm getting a quote from a local installer but would like to get some feed back from you folks. You might have to ask me questions so we can get the right feed back going.

Most of what I'm wondering is if there is much performance and or maintenance difference between a rigid smooth liner and a regular flex non-smooth liner.

 

[mark cline]

My opinion , I would go with a rigid smooth liner. I think the smooth can take a bit more when cleaning with a brush. A bit more expensive, but I think the difference is worth it.

 

[Woody Stover]

Don't get a flex liner unless you have to (not a reasonably straight shot up the chimney.) Rigid is more durable and drafts a little better.

A bit more expensive, but I think the difference is worth it.

Actually cheaper than a heavy duty flex liner in the brand I got....

 

[Charles1981]

I had to push fairly firmly when cleaning my 6 inch rigid liner for the first time the other day. I've felt the flex liners and they are tough, but I feel way more comfortable ramming a brush down there with it being rigid liner...but it was pretty darn expensive for 26-27 feet. Lots of people here though have flex liner and have no problems sweeping so...in the end it probably doesn't make that big of a difference.

 

[Benchwrench]

I chose rigid because it was a straight shot and the best choice for my 2 story install, no corners cut.
for the offset to the stove I went with ArmorFlex and I would recommend that stuff also.
You can see my install here: https://www.hearth.com/talk/threads/a-square-peg-in-a-round-hole.71287/

lots of pics too.

 

[Hogwildz]

Both are capable. Rigid is superior and tougher. You can get double wall per-insulated rigid, and it is a great liner. I used it in my install, and am glad I did.

 

[Watchguy]

My first impression was with rigid liner. Sounds like this is confirming it. Just got the estimate today for the install. They want a little over $1500.00 plus tax. That's a little more than the price of the Selkirk UT I originally installed (myself).

Thanks for the replies.

 

[Benchwrench]

My first impression was with rigid liner. Sounds like this is confirming it. Just got the estimate today for the install. They want a little over $1500.00 plus tax. That's a little more than the price of the Selkirk UT I originally installed (myself).

Thanks for the replies.

Do your homework and Ask questions before hand as what you will be getting regarding what product and procedure. I found Just my parts cost was well over $1000.

One local installer was going to "fabricate" a liner from a buddy's sheet metal shop. That's when I decided to do it myself.

 

[fire_man]

I agree, go with rigid for all the reasons above.

I had many installers barf at the idea of installing rigid and tried to talk me out of it - it's more of a pita than flex to install.I ended up doing it myself.

 

[thechimneysweep]

At the risk of starting a flame war here, I feel you should hear from someone with a little more experience. We've installed and serviced both kinds over the past 38 years, and we prefer flex. No joints to come apart during vigorous sweeping, for one thing. Further, we've found that the increase in creosote formation due to reduction in flow rate cited above is undetectable, outside the test lab (we don't find any more buildup in corregated liners than in smooth). And, contrary to what seems to be popular forum opinion, we've found the "action" created by the corregations at the tips of the brush tines makes flex much faster and easier to sweep, particularly if there's any glaze present. The titanium-blend stainless flex liner we carry is far less expensive than rigid, much easier to install, and has a lifetime warranty. With hundreds of installations in place, and decades of annual sweeping, we've encountered far more problems with rigid liner installations than flex.

 

[Woody Stover]

The titanium-blend stainless flex liner we carry is far less expensive than rigid, much easier to install, and has a lifetime warranty. With hundreds of installations in place, and decades of annual sweeping, we've encountered far more problems with rigid liner installations than flex.

That's a lightweight liner, like HomeSaver Pro or Ultra, right? I'm no expert but after seeing a few pics on here of over-fired liners that separated, for my own peace of mind I put in HomeSaver RoundFlex. When they say "heavy duty," they ain't kiddin'; That stuff weighs a ton!

What kinds of problems have you seen with rigid liner installs?

I didn't really buy the "better flow" argument either. Seems like the corrugations of the flex would mostly fill in with creo, and once you get a little creo on the rigid, it's gonna be pretty much a wash I'd think. That said, at this time I would still go with rigid but I'm open to hearing another point of view....

 

[BrotherBart]

I'm no expert but after seeing a few pics on here of over-fired liners that separated

Could you point to some of those posts? I must have missed them.

 

[thechimneysweep]

What kinds of problems have you seen with rigid liner installs?

A few that come to mind:
RIgid liners must be installed in sections. Each joint provides an opportunity for air intrusion into the exhaust flow, which can interfere with proper draft.

Over time, creosote can corrode the screws which hold the sections together, compromising the connections. Even if stainless screws are used, metal expansion and contraction can cause them to loosen over time. After experiencing rigid liner joints coming apart inside the chimney when we swept them, (a nightmare), we learned to use stainless rivets, but have had them come apart too.

Fireplace insert installations typically require a few feet of flex at the bottom, to line up with the flue collar. We never did come up with a satisfactory fastener for the connection from the flex to the rigid, and that's the area that is subect to the most stress at sweeping time.

 

[bholler]

we have been sweeping for 35 yrs and installing liners for 30 or so and we almost never use rigid either. but for wood we always use heavy flex like armor flex. but I know lots of guys install light wall stuff and it usually works fine but just in the past year we have pulled 3 light wall liners installed by others that were burn through. and we did pull one heavy wall that we installed 27 years ago and was hooked to an old fisher insert used as the only heat source for the house which we didn't think was a bad lifespan and the customer was not upset either. most of the problems we have had with rigid are installing. you might think your chimney is straight but when you start putting a perfectly straight pipe in it better be really straight or there are going to be problems. but if the install is done right rigid is a very good and durable liner for sure. .

 

[Watchguy]

I'm starting to lean more toward just chucking the old chimney and installing a new one for about the same price as lining it. Got to figure out how to deal with down sizing the roof flashing but other than that it's not like it's that hard of a job.

Thanks for the input.

 

[bholler]

I think that is the best option

 

[fire_man]

Thechimneysweep makes some really good points which I have heard before but were well stated here.

Maybe I am just caught up with the sheer incredible weight difference, which is huge. It seems like rigid would hold up longer and survive a hotter chimney fire. As far as the joints go, I taped each joint with high temp tape, and used SS band clamps as well as SS hardware to hold the joints together.

Yea I know the high temp tape might fall off but my flue temps are very low on my stove so it might just last (below 300F on exterior surface of single wall stainless 10" up from T). I agree, the joint between the rigid and flex in the smoke shelf is a week point, but the soot eater seems to be pretty delicate.

 

[Woody Stover]

Could you point to some of those posts? I must have missed them.

I realize the damage shown in this post was most likely due to frequent over-firing, and the liner brand and model was never identified, but when I see stuff like this I'm glad I tend toward overkill. I feel pretty good with that tank of a liner in there.
https://www.hearth.com/talk/threads/liner-pic-i-am-stumped-and-discouraged.109403/
You posted in this thread. BTW, some guests on the Diane Rehm Show were saying there's evidence that fasting may slow the progression of dementia. Just a heads-up. My memory was never too good to begin with so I really have nothing to lose.

 

[BrotherBart]

Yeah that was the product of delamination that is the problem I have with the "smooth wall" liners. That and the fact it was installed upside down.

But it did not come apart. Or as you said "that separated". There was still a .006 liner wrapped around the outside of it that didn't bust.

 

[_CY_]

just finished installing 8in smooth wall stainless liner the entire run including final bends. used two 30degree stainless elbows and short 18in straight for final connect. interlocks designed into all connections except 30degree elbows, which was screwed down. started to use stainless rivets but used screws so it could be taken apart without fuss.

used Majestic SK Series 8 in. Diameter Wood Burning Double Wall Flue Sections .. local fireplace warehouse had tons in stock at much cheaper than online prices. paid $40 for a 4ft section or about $10 per ft vs online prices of about $92 for 4ft section .. shipping really adds to price.

didn't measure thickness of stainless liner but it was beefy!
NO way that's burning out for quite sometime, if ever ..

just didn't like the sound of using much thinner stainless flex. too much chance of tearing during cleaning. another thing I didn't like was the short life ratings when I talked to actual mfg tech guy.

 

[Woody Stover]

it did not come apart. Or as you said "that separated". There was still a .006 liner wrapped around the outside of it that didn't bust.

No, I didn't mean to imply that the liner was breached. I remembered another thread (couldn't find that one) with a pic up the inside of the flue, where a ply was buckled in (separated) from the rest of the liner wall, but I don't think he had gotten to the point of taking the liner out to see what the actual damage was.
Regardless, if I had a straight shot, I would have put rigid in here, but I had to go with the flex. Being the overkiller I am, I got the liner with the thicker material and no seam. Clearly they all have been tested to UL, and as long as they aren't abused they'll do the job. But over time I have to think the heavier liner will last longer and in the event of an over-fire, hold up better.

 

[BrotherBart]

No question. In most cases, done right, heavier is better.

 

[Woody Stover]

just finished installing 8in smooth wall stainless liner the entire run including final bends. used two 30degree stainless elbows and short 18in straight for final connect.

That's how we did my BIL's downstairs stove, but into a tee. It was nice that we could keep it all solid pipe, no flex, all the way down.

 

[_CY_]

That's how we did my BIL's downstairs stove, but into a tee. It was nice that we could keep it all solid pipe, no flex, all the way down.

what soooo amazing is the heavier rigid stainless liner was less than 1/2 of online price for stainless rigid or stainless flex with flex being the last option due to short lifetime rating by actual manufacturer of stainless flex duct. I believe 10 years was rated life for flex duct vs Majestic double wall rigid liner were stocked for permanent new fireplace installations, not wood burning inserts.

the other wood stove store in town was charging an unbelievable $100 per ft for 8in rigid or flex stainless. for an 18ft total run of 8in stainless liner including short 18in/24in sections and two 30degree elbows .. local costs was under $200 vs online costs for same duct would have been $500+ .. stainless flex duct was about $350-$400 online

moral of that story is ... please do check with your local fireplace warehouse before buying online. you just might be pleasantly surprised. it's always best to support local businesses .. most importantly was able to purchase extra duct of varying lengths. then take back what was not needed. very important when working with rigid.

 

[bholler]

actually heavy wall flex liner is much heavier than rigid liners. and I have seen many light wall liners both smooth wall and regular that have been completely burnt through. one in 2 seasons. only seen 2 heavy flex liner burnt through and one rigid that was not exactly burnt through but it was melted at the bottom and collapsed on it self. rigid is probably a little more durable than heavy flex but not by much and like chimneysweep said those seams can definatly be a problem. and if you use rigid make sure you assemble it right side up or you will have creosote running down the out side eventually and that is a really bad situation.