Flex liner claims are hogwash

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fire_man

fire_man

Minister of Fire
Feb 6, 2009
2,702
North Eastern MA
One of the selling points for flex versus rigid liner has always been manufacturers claiming flex liners are "self cleaning" of soot/creosote since thermal expansion and contraction tends to cause the residue to fall off.

I just pulled an old 13 foot rigid liner attached to 3 feet of flex at the smoke chamber. Guess where all the thick soot was? Yup - thick and heavy in the flex liner (even in the straight section) and thin to non existent in the rigid liner. I would have thought the pipe closest to the stove should have been the least sooted. So much for those claims - I have always believed rigid is better because its thicker, smoother and straighter - although rigid is almost impossible to install in many situations.

I called 3 installers to get an estimate to reline and insulate a new identical rigid/flex setup. All three recommended flex because its "safer" and "better". Hogwash. It's just easier to install.

Rant over.
 
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That's interesting Tony. Go ahead and rant if you wish.
 
Which manufacturers claim that? I have heard other people say it but not liner makers.
 
Do you use a soot eater? I have one and my plastic brush broke up lots of creosote it left behind. But I use a string to pull the poly head up and down the liner, and since I have a 2 story metal roof to stand on while doing it, use the soot eater more.
 
If you have that much soot in the smoke chamber section, you may not be burning hot enough, or dry enough wood. That kind of stuff should be at the top.
 
This came right off the Rockfordchimneysupply.com FAQ site:



Even though flexible liners have a corrugated surface, they tend to collect less creosote when used to vent wood fireplaces and stoves, because they flex as they expand and contract with temperature fluctuations, causing buildups to loosen and fall away. The ease of installing flexible liner far outweighs any difference between the rigid and flexible liners. (HOGWASH!!)

I hear you Hogwildz on needing to burn hotter, that soot is leftover from the tail end of last year's shoulder

season burns. I was not engaging the cat and burning some small fires to take the chill out.

I use a metal brush and pull it down from the top using a steel cable. This lets me clean while the flue is hot, which is why I don't use Poly brushes.
 
I agree that self cleaning is BS. All liners "self clean" a time or two when new, from expanding and a still smooth, slick surface. I was worried when i heard the crap falling down the rigid into the insert at the first few cold start ups at new. That didn't last long. Everyone has a sales pitch, some more far fetched than others.
 
I have 27' of flex liner and I find a lot of the nasty stuff falls off over the summertime. I always have good intention of sweeping after the stove is done in the spring but never do, when I sweep in the fall I usually find most of the stuff has fallen off the liner during the summers heat/humidity.

If you had a lot of thick soot near the stove I would look for a leak in the lower part of the pipe somewhere. How thick are we talking about?
 
BrotherBart said:
Which manufacturers claim that? I have heard other people say it but not liner makers.
Click to expand...
Not a maker, but I remember hartshearth.com said something like "flex liner will collect a little more but not that much to be concerned about." Nothing about "self-cleaning." Although different stoves were on these liners....my exterior masonry chimney, insulated flex liner had maybe three or four cups of crumbles in it whereas BIL's, same specs except rigid liner, had about a handful of powder. Both of us should do better this year with drier wood.
 
rdust said:
If you had a lot of thick soot near the stove I would look for a leak in the lower part of the pipe somewhere. How thick are we talking about?
Click to expand...
Click to expand...

The rigid liner had about 1/10" of soot, the flex near the stove was noticably thicker. At the very least, it was certainly not less soot than the rigid, my point being some manufacturers claim flex sheds better.

As for leaks, that's an interesting point - but I would have thought at least some of the rigid pipe would have had as much soot as the flex. The whole system is brand new, so any leaks should be gone.

That is the one weak point to rigid - there are more transitions that can cause leaks.
 
Flex King has a smooth inner walled flex liner. Probably not as flexible as most flex liners but would be easier to install than ridgid.
 
Interesting claim, I guess it could have merit for the first few feet where it is hotter, maybe with an insulation wrap it contracts more? I overlooked that claim as I just clean it anyway, I do not trust anything that says self cleaning, even the oven, but it does help get it clean.
 
Todd said:
Flex King has a smooth inner walled flex liner. Probably not as flexible as most flex liners but would be easier to install than ridgid.
Click to expand...

Yep. I had a few different quotes on my install, scheduled for next week, and a few of the installers made a point to differentiate between standard flex and "smooth wall flex". I don't know anything about it, aside from what the name implies. Rigid would have been a difficult proposition in my particular install.
 
Something you have watch with the "smooth wall" flex is the outside diameter. Since it is two plies it is significantly bigger around than single wall flex. I know, there is thirty feet of it laying in the edge of my woods getting used a piece at a time for stove pipe on the outside stove because it wouldn't fit down my 7X11 chimneys. Very expensive outside stove pipe. <>
 
Good to know! However, my original flue is large enough to make Santa Claus coming down it plausible, so there's likely no problem there. I honestly think they could've fit rigid down there, but there is one nasty offset near the top that might have made a blanket-wrapped rigid a little tight.
 
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