therm said:
Newbie here with a few basic questions about chimney liners.
1. Is an insulated liner intended to protect the surrounding masonry (safety) or to improve the draft of the chimney (performance)?
Both... It is a REQUIRED part of the installation if your chimney is not NFPA compliant to begin with - which isn't always easy to tell, and it will give an increase in safety even in a good chimney. It will also help to improve the performance of most chimneys, particularly exterior chimneys in colder climates. Warm climates and / or interior chimneys will get less benefit.
2. Is the insulation an integral part of the liner or is it wrapped around the liner at installation time? Is it Kaowool or another material?
It's an external blanket that gets wrapped around the liner, and secured with a special tape, then covered with a stainless mesh "sock" that is intended to protect it while sliding down the flue. I'm not sure just what the material is, but it's probably similar to Kaowool.
4. What is the purpose of a double-walled liner? Is it in lieu of insulation or for a different purpose?
Some rigid liner is double wall with insulation built in, so no external insulation is needed. In the case of flex it is claimed to be more durable / better safety, and / or give a smoother interior surface but does not substitute for insulation, and some claim that flexing the liner actually causes it to become less smooth than a single wall liner.
5. Round vs. oval liner. Why would you use one over the other?
Round is generally less expensive than oval, and may have greater cross sectional area for a given size (depends on whether it is a manufactured oval, or an "ovalized" round size) but can have problems going down some rectangular flues. Oval can fit better in such cases. In general, I would say use round if you can, oval if that's what it takes to fit... Some people will also ovalize the bottom few feet of a liner to get it past a damper or other restrictions in the smoke box area, however it is best to minimize this as much as possible.
6. Rigid vs. flexible liner. Is this mostly a matter of installation difficulty, i.e. rigid for straight runs and flex for runs with turns?
That's about it. In theory rigid is smoother inside so it will perform slightly better, develop less crud, and be easier to clean, but in practice it doesn't seem to make a lot of difference. Note that it is also possible to do a combined install with mostly rigid except for a few feet of flex on the bottom to get through the smoke shelf / damper area, and connect to the stove.
7. "304" vs. "316ti". Are these stainless steel alloys? Is 316ti better but more expensive?
Yes, those are the alloy numbers, with the "ti" indicating the presence of Titanium in the alloy. - the 316ti is generally considered the better of the two, although it does not appear that UL considers it so much better as to not need insulation in a non-compliant chimney.
I recently purchased a Jotul Kennebec wood insert and am waiting for the installation. I also bought a 25' stainless steel liner for $680. I'm assuming this is a rigid single-wall non-insulated liner, but I don't know for sure. I have a 25' chimney, the lower 10' of which is interior and the upper 15' of which is exterior. The chimney has an 8" x 12" clay-lined flue and seems to draft pretty well based on many years of open fireplace fires. My question is, what would be the best type of liner for my situation?
Thanks in advance for any advice. I'm sure some of the answers are to be found in prior threads, which I'll search.
I would try to insulate the top 15' or so, you don't have to get the same length insulation kit as you do the liner, and there isn't as much benefit to insulating the lower part of the chimney. However, you should note that your nominal 8x12 flue will actually be considerably less than that, so getting an insulated 6" liner down it can be a challenge. I've heard a few folks suggest that a 1 gallon paint can is about the same size as an insulated liner, so seeing if one can drop an empty can on a rope down the chimney can be a good "fit test".
I would also point out that in addition to the liner, you should definitely put in, or insist that the installers put in, a blockoff plate - there is a wiki article describing them, and I would consider that a vital part of the installation - to the point of saying it is a non-acceptable job if one is not put in. We've had multiple reports of people finding their inserts performing badly, and then getting great improvements after putting in the blockoff plate so their heat comes out into the room instead of going up the chimney.
Gooserider
