Ovalized liner or cut out larger damper (sic?) opening?

[Gooserider]

The insulation is normally a blanket that gets wrapped around the liner and glued / taped in place, with a metal mesh "sock" that gets pulled over the liner & blanket to hold everything in place while you slide it into the chimney. Ideally the liner should be insulated from about the 1st flue tile up for best performance advantage. In any case you should definitely insulate the part that sticks out above the masonry. The insulation blanket is usually 1/2" thick, so it will be a bit of a squeeze to get it into a 7" pipe - 8" would be better, but you might get away with 7".

If the chimney is not already NFPA-211 compliant (tile lined, in good repair, built w/ proper clearances, etc) and the liner is being installed to make it comply, then the insulation is required by code. If the chimney is NFPA-211 compliant, and the liner is being used simply to meet cross section requirements, or for ease of cleaning, then the insulation isn't strictly required, but will probably improve your performance. The basic idea is that the hotter you keep the stack interior, the better it will draw, and the less creosote you are likely to build up.

In terms of the pipe you use for the extension, I don't know of any strict limitations on what material is used, however a lot of folks prefer to use stainless on exterior parts because it looks better for longer when exposed to the weather, and may last longer.

The hearth pad is another issue that is a bit more complex than appears at first glance - The first step is to look in the manual for the insert, and see what it says about requirements for the floor protector. Some units have minimal requirements, and will merely say something to the effect that they need a "non-combustible surface" and virtually anything that won't burn will meet the requirement. Other units will require some level of insulation, the "nice" manuals will say something like "hearthpad made from non-combustible materials with a minimum R-value of ???" The "PITA" manuals will say something like "hearthpad made from <thickness><material> or equivalent". The idea is that the hearth pad must not only withstand possible flaming logs and embers getting dropped on it, but must also prevent the heat radiated by the insert from overheating the combustibles under it. The value in the manual is a minimum requirement that has been determined by testing as part of the stove's certification process. It will never hurt to exceed the minimum.

IFF your manual says "non-combustible surface" the soapstone slab should be fine, however if an R-value is stated, it almost certainly won't be, as stone has negligible R-value. There is an article in the Wiki on hearth construction, with details, but essentially you need to build a "sandwich" of insulating materials to reach at least the required value, which is usually then covered with stone or tile for cosmetic sake.

Gooserider

 

[Rhone]

That's a strange liner configuration. Insert liners are either flex at the base for like 4-6 feet to get them through the damper area & the few bends at the end then rigid the rest (as is my case). Some people have flex the entire stretch, which I don't recommend in ranches with short roofs (you risk problems) otherwise they're fine.

There's 2 normal ways of insulating. Liner insulation, which is Kaowool that looks like a thin layer of white fiberglass on one side, and aluminum foil on the other (aluminum side goes on the outside). It's not thick, you have to allow heat dissipation in the event of a chimney fire which can reach over 2000F. Read the instruction for your liner as some allow only 1/4" of insulation others allow up to 1/2". The insulation comes with a sort of metal springy netting, you simply wrap the insulation around and put that springy metal mesh around it, and push it down the flue. Of course, the size of your flue determines if it's practical or not as there's practically no way a 7" flue will fit a 6" insulated liner down it. Works with both rigid & flex liners and cheap. It is a product specifically built for insulating chimney liners, don't try to invent your own insulation scheme, and just as important read your liner instructions to see what they allow.

The other method is double-wall, far as I know both are stainless for wood burning units, they commonly use a twist & lock sort of mechanism. This is deemed inferior to the other method as condensation can form between the two pipes.

Now, I've not heard of getting a 7" rigid liner and putting a 6" flex inside. Do a search on here about using galvanized chimney liners, it's been discussed before and there are issues with them but most are people trying to avoid the costs of using stainless liners rather using steel or galvanized from the stove to the outside. It sounds like you have the stainless liner, and want to put galvanized on the outside of it which I've not seen or heard. I do know galvanized at high temps vaporizes to turn into poisonous gas but, not sure with it on the outside what will happen here.

The way you're doing it, you need a flex to rigid adapter at the top of your chimney, and the same brand as the adapter stretch of Class A pipe. Probably needs to be fastened well to the chimney against wind.

 

[Hogwildz]

That's a strange liner configuration. Insert liners are either flex at the base for like 4-6 feet to get them through the damper area & the few bends at the end then rigid the rest (as is my case). Some people have flex the entire stretch, which I don't recommend in ranches with short roofs (you risk problems) otherwise they're fine.

There's 2 normal ways of insulating. Liner insulation, which is Kaowool that looks like a thin layer of white fiberglass on one side, and aluminum foil on the other (aluminum side goes on the outside). It's not thick, you have to allow heat dissipation in the event of a chimney fire which can reach over 2000F. Read the instruction for your liner as some allow only 1/4" of insulation others allow up to 1/2". The insulation comes with a sort of metal springy netting, you simply wrap the insulation around and put that springy metal mesh around it, and push it down the flue. Of course, the size of your flue determines if it's practical or not as there's practically no way a 7" flue will fit a 6" insulated liner down it. Works with both rigid & flex liners and cheap. It is a product specifically built for insulating chimney liners, don't try to invent your own insulation scheme, and just as important read your liner instructions to see what they allow.

The other method is double-wall, far as I know both are stainless for wood burning units, they commonly use a twist & lock sort of mechanism. This is deemed inferior to the other method as condensation can form between the two pipes.

Now, I've not heard of getting a 7" rigid liner and putting a 6" flex inside. Do a search on here about using galvanized chimney liners, it's been discussed before and there are issues with them but most are people trying to avoid the costs of using stainless liners rather using steel or galvanized from the stove to the outside. It sounds like you have the stainless liner, and want to put galvanized on the outside of it which I've not seen or heard. I do know galvanized at high temps vaporizes to turn into poisonous gas but, not sure with it on the outside what will happen here.

The way you're doing it, you need a flex to rigid adapter at the top of your chimney, and the same brand as the adapter stretch of Class A pipe. Probably needs to be fastened well to the chimney against wind.

Just for the record, the double wall I used is insulated between the layers, and no condensation problems And instead of twist lock, this has an inner & out lip, the pcs slide together into each other & are riveted with 4 s.s. rivets each section.

 

[Daniel]

All good points. Right now it looks like my insert and flex liner will be a perfectly straight run without any bends, twists, or turns. My chimney is only 12' high so the reason I'm using the 7" rigid liner is to support the 3' flex liner that will run up thru it. This will give me 15' even on the chimney and meet Napoleon's spec. I will either insulate the outside of the 7" rigid liner with insulation and mesh netting or wrap the 6" flex liner with insulation and then put the 7" rigid around it. The 7" rigid has a slot and groove set up and I could use large hose clamps to make sure it does not come undone. Thanks for all your opinions, insights, and help.

 

[Hogwildz]

All good points. Right now it looks like my insert and flex liner will be a perfectly straight run without any bends, twists, or turns. My chimney is only 12' high so the reason I'm using the 7" rigid liner is to support the 3' flex liner that will run up thru it. This will give me 15' even on the chimney and meet Napoleon's spec. I will either insulate the outside of the 7" rigid liner with insulation and mesh netting or wrap the 6" flex liner with insulation and then put the 7" rigid around it. The 7" rigid has a slot and groove set up and I could use large hose clamps to make sure it does not come undone. Thanks for all your opinions, insights, and help.

I strongly suggest not putting the insulation on the outside of the rigid. For 1 it will be exposed to the weather, and prolly won't last too long, point 2 is it will look like sheet. Will do more good & look better & last longer between the rigid & the flex IMO. I am stating this assuming the rigid will be above & outside the existing chimney?

 

[Harley]

Some people have flex the entire stretch, which I don't recommend in ranches with short roofs (you risk problems) otherwise they're fine.

If the liner is at least the minimum height recommended for the stove, and the chinmey meets the 10-2-3 rule... is there any reason you would run into problems with a flex liner on a ranch with a short roofline? I'm trying to figure out what other problems you could run into.

 

[Rhone]

Not that I'm aware Harley, as long as you meet the generic minimum length I think the house mostly irrelevant. Most ranches with a short roof (that is low pitch) that I'm familiar with have around 12' chimneys, mine and a friend at work are that way. We both were having draft problems, he extended his chimney and told me he couldn't believe the difference and what prompted me to get an extend-a-flue as part of my major overhaul to improve my draft.

A flex pipe, ovalized, through damper, and 12' long will work but you have a risk of problems usually during warmer weather. My insert with a liner at 12' long, ovalized, and mis-matched was unuseable unless 45F or less outside just couldn't draft. I was irritated to turn on oil heat, and since draft stunk my glass would get dirty until it hit 20F- outside. But, at least at 20F or less outside I got enough draft for things to run smoothly. I extended my chimney from 12' to 16' in total and improved other draft problems and now even when it's 58F outside I can have a fire going and on reloads only a hint of smoke will pour into the living space, and pretty much the glass has been spotless since. But, as far as I can tell between my coworker and I the difference between 12' and 15' is really noticeable on draft and if you get 15' you'll get a lot more enjoyment out of it (that's to say, it's best to work on getting 15' in our opinions than trying to do things to make it work with 12').