Why bother with Class A pipe for an exterior extension of a single wall flue?

[fire_man]

I added 30" of single wall exterior pipe at the beginning of this heating season to my 15' single wall insulated flue as an inexpensive experiment to see if it would improve the draft of my short chimney. I expected to have to convert to a Class A exterior extension if it worked, since I expected the exterior single wall pipe to be crusted with creosote being exposed to one of the harshest cold winters in history.

The results amazed me - The cat lit off much easier, and the ENTIRE flue including the 30" exterior extension was nearly perfectly clean at the end of the heating season. Every other year I burned this stove I got close to 2 gallons of fluffy soot (without the extension) and had problems getting the cat to light off. I have always burned wood seasoned 3+ years.

So the extension worked but now I'm wondering why should I bother swapping the extension to Class A?

 

[Chinneysweep187]

Draft is dependent on outside and inside temperature differential and chimney height. So theoretically the higher chimney the stronger the draft, no brainer.Solid fuels need insulation around the liner , for proper expansion and contraction of the liner and also to keep the liner hot. No insulation around that section of the pipe In my opinion will lower the lifespan of the pipe and cause it too cool down rapidly and make creosote and also glazing which is different . I didn't see your pipe I don't know how bad it was but you also could have been burning super hot and with good wood making minimal creosote. I would just get a 4ft section of class a which is 100$-175$ where I live and install it yourself . I would also grab a transition plate which converts normal single wall to class a . Take off your liner cap and connect the anchor plate . That way the class a is supported . Anything 4ft out of the roof should have a roof support brace though, but they are really ugly In my opinion

 

[fire_man]

Agreed the supports are ugly and I'm not sure how I would support above the crown of a masonry chimney. I was hoping to go with 36" and forget the bracing. I'm not familiar with the transition plate for a single wall to a class A but would have thought it would be pricey.

Good thought on the possible glazing of the extension pipe I need to check for that.

 

[Chinneysweep187]

A 36" piece with a transition plate would work fine and transition plates aren't that expensive but find out for yourself . Also i don't know what your chimney looks like but if your handy you could consider raising the masonry chimney with more block or brick. Remove the crown , add desired height , back fill w/ insulation and put a new crown on .

 

[fire_man]

Wish I had the ambition to add 3 feet to the masonry. It's a 6' x 2' chimney so a lot of work.
I inspected the extension and there was some minor glazing on about 15% of the pipe but nothing major.
It just seems for all the extra work of changing over the plate and the > $200 I'm still not sure it's worth it for the Class A pipe.
I know it's the right way to go code wise but it seems so unnecessary based on my experience.

 

[Chinneysweep187]

Yeah 6' x 2' is a lot of work no doubt . but I consider 15% to be horrible . The liner is supposed to work being the size that it is . You just downsized it that much and to be only 1 season . Not only that ,glazing and creosote is made from tar fog from the wood that is high in moisture so that part of the pipe is not only smaller than it should be but also cooler and wetter. That will only increase the creosote /glazing made. If it was 15% glazing this year it could very well be 30% or more next year which is 45% half of the original pipe size . Then you have two issues, too much smoke is made and is impossible to vent out because of size restrictions , which blows back in the house . Also the glazing will dry out and become highly combustible starting a chimney fire which would likely catch any other creosote in the system up and ruin the liner / bigger problems . What are you gonna do replace that piece of pipe you have every 2 or 3 years and even so the downsizing will cause may more glazing / creosote in the entire system when that class a extension is good for life and will not obstruct the liner whatsoever . If you think it's worth it to constantly replace it , by all means but I would spend the money now and make it last . At my company to install that would be around $400 or maybe a smidge more $200 or less is a steal.

 

[fire_man]

When I said 15% glazing, I meant about 15% of the surface area was covered with a film that was shiny but not even paper thin. Perhaps this is not what you meant by "glazing". The thickness was not even measurable, just a shiny color of black. I know Class A is the correct solution, but after pushing 4+ cord thru a single wall extension and getting almost zero buildup (other than some minor flakes and paper thin glaze, I just don't understand the need.

I'll try to post a picture this week of the extension- I removed it and capped the exit for the summer since it just looks funny popping out of the chimney crown so far. I imagine if I replace the old plate with the new transition plate, I need to be careful since the solid pipe below (not flex pipe) will be heavy and want to drop.

All good advice above - I definitely appreciate the responses. This site is quiet this time of year.

 

[Chinneysweep187]

The shiny thin stuff is glazing and believe me will increase exponentially . If you don't care about codes and what not at the very least find a way to insulate it. get a double wall pipe and stuff ceramic wool insulation inside and attach to the top but don't leave it as it is . That's all a class a is . A double wall pipe with insulation in between .

 

[Chinneysweep187]

Air is even a good insulator and double wall is better than single wall

 

[fire_man]

All makes good sense. I always figured class A was just insulated double wall but never knew for sure.
I'm thrilled such a small change in flue height made such a difference in cat light off and lack of creosote.
Now I just have to get the pipe part right.

 

[bholler]

I always figured class A was just insulated double wall but never knew for sure.

Not exactly class a has 1" of insulation and is tested to be used as a chimney double wall connecter pipe has 1/2" air space and is just a connecter not a chimney. But yes basically class a is 2 layers of pipe with insulation in between them.

 

[fire_man]

Thanks bholler.

All I know for sure is Class A is a heck of a lot more expensive than single wall and I wish my single wall extension was clogged solid. That way it would have been a no brainer to replace it with the right stuff.

 

[bholler]

All I know for sure is Class A is a heck of a lot more expensive than single wall and I wish my single wall extension was clogged solid. That way it would have been a no brainer to replace it with the right stuff.

yeah it might work ok as it is but it will work better done correctly

 

[Chinneysweep187]

Not exactly class a has 1" of insulation and is tested to be used as a chimney double wall connecter pipe has 1/2" air space and is just a connecter not a chimney. But yes basically class a is 2 layers of pipe with insulation in between them.

Bird up . I wasn't sure what the air space was between the pipes in either situation .

 

[bholler]

Bird up . I wasn't sure what the air space was between the pipes in either situation .

It would work if you where able to stuff it completely but it would not be water tight and i don't know how you would anchor it or terminate it well.

 

[Chinneysweep187]

yeah it might work ok as it is but it will work better done correctly

Not to mention done correctly ,you don't have to worry or check the pipe every couple months can sweep it and be done

 

[Chinneysweep187]

It would work if you where able to stuff it completely but it would not be water tight and i don't know how you would anchor it or terminate it well.

That's for him to figure out I suppose I don't know either

 

[bholler]

That's for him to figure out I suppose I don't know either

Haha i guess so

 

[Chinneysweep187]

Just get the class a and be done with it bro

 

[fire_man]

Yea Yea I know just do the Class I know that's the right answer. It's just with 2 kidlings just shy of college by a few years every penny adds up and I look for ways to save .

 

[Chinneysweep187]

Well like I said I would stuff a double wall pipe with ceramic wool and call it a day . I know money is tight sometimes

 

[rideau]

Tony, Maybe post on CL that you need 3 -4 feet of Class A chimney pipe? Maybe someone has little and you could get it cheap.

 

[madison]

Why bother?
1. Could be a code violation, once you transition to class a - you maybe required to maintain class a until termination at the cap - though it sounds as if there is no class a pipe currently inline.
2. Also in support of the code, it could be a fire hazard to have non insulated pipe above/beside your home.
3. Strength, class a would be stronger