flexible uninsulated or a combo of flexible/rigid insulated stove pipe-pros & cons??

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natinstl

New Member
Jan 3, 2008
6
WA
We will be purchasing a Jotul Nordic that will sit on our hearth and the stove pipe will go from the back up through our existing chimney. One dealer has given us a quote using all flexible uninsulated pipe and the other has given us a quote that has flexible pipe coming out the back and then the top five or six feet is rigid insulated pipe. The price difference is pretty significant in terms of installation. The all flexible cost is $500 less in installation than the rigid cost. Is there any significant reason why we should go with the rigid vs. all flexible liner. It's a reliance liner system if that makes a difference and we're in the Pacific NW.
 
How tall is the chimney? Is it an interior or exterior chimney? Are both dealers quoting with a block off plate installed below the damper?
 
I'll have to get the exact size later, the install guy actually said it was the correct height whatever that means. It is an exterior chimney and neither has mentioned a block plate.
 
It's hard to comment on the chimney without knowing it's construction and height. Does it have a tile liner? If yes, what size?

With an exterior chimney in a mild climate, an insulated liner will help draft. Especially when the temps are above 35-40.

As to the block-off plate - check the manual:

"A new sheet metal damper block-off plate must be installed around the connector pipe at the damper
frame and sealed with the proper sealant (usually High-Temp Silicone)."
 
We are installing a new liner at this time also. Our chimney is tile lined, but even if it wasn't I'd take the same approach. We're installing a rigid liner and insulating the part of it that goes above the roof line. (last 7 feet) We are also installing a block off at the top and since it has a woodstove thimble in the chimney (see avatar) we are insulating around the timble connector. This will give us heat sheilding above the roof line where it is colder and create dead air space all the way up the stack where the liner runs. Our goal is to provide a flue that has good heat retention and avoids creosote build up.
With no existing liner in the chimney the SS liner will protect you but you also need to keep that liner's evironment as warm as possible.
If you have an outside chimney, I'd say you have to insulate it all.
 
Old exterior chimney, no liner - I believe that an insulated liner is required in this situation. Be sure your bids are for the full job.

The installer should have told you this. Is this installation getting permitted or inspected?
 
As to the question of rigid vs flexible liner:
My understanding is that ...
1. flexible liner requires a softer cleaning brush and being more careful when cleaning than rigid pipe.
2. rigid liners are smooth inside, so creosote tends to fall off easier on its own than would in a typical flex liner.
3. rigid liners with smooth insides supposedly draft better than a flexible liner without a smooth inside.
4. rigid liners are heavier and more durable in the long term than flexible liner.
5. rigid liners are more difficult to install than flexible.

I also understand that not all flexible liners are created equal. Some have better methods of construction than others. Some are thicker gauge metal than others. Some have different designs that allow for smoother insides than others.

Perhaps someone with more experience can elaborate.

However, I think your choice may be dictated by the need for insulation in your unlined chimney. Insulation would be not so much for draft improvement, but to protect the wood outside your chimney from igniting in the event of a chimney fire/ metal liner failure. A third option would be to investigate a cast in place /air bladder chimney flue system.
 
Elmo said it well.
I have 5' of flax at the bottom with 22' of double wall factory insulated the rest of the way.
Cleaning is a breeze, draft is to die for, and its just a premium set up all the way around.
If you can afford it, I'd suggest it. If not, at least get the flex liner insulated. Go the extra mile the first time, save any possible potential head aches down the road.
My rigid was no harder to install than flex. Matter of fact, aside for me doing it myself and it can get heavy on the arms, it was tons easier than the flex I helped Newtown install. Of course his was a very tight fit, rigid would not heave went down his chimney without reducing to about 5" at least.
 
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