Chimney Liner in a 7x11 Flue

[tdibiasio]

I am replacing my Lopi Insert this summer with a BK Princess insert I am also planning to install a full length SS flexible liner. I have studies the options from the normal vendors (Chimney liner Direct\woodland direct\Northland express). Before pulling the trigger on all the components I was hoping to get a little advice. First, here is the specifics about my chimney set up - Center of the house chimney approximately 23' to where it will connect to the stove, three terra-cotter flues (one for furnace\one for the new BK\one unused flue all the way to the basement). At the top I have a big SS cap\spark arrester that covers all three flues. Without climbing all the way up there to measure the flue size I simply measured the brush I use to sweep - the approximate measurement is 7x11 so I am assuming the flue size is in fact 7x11.

So now to my question - I was considering purchasing a double wall flexible liner and adding to the .5" insulation blanket. But now I am getting concerned if this will even fit down the flue?? The flue is in good shape as far as I know as I am the one who sweeps it each year. There is only one real bend in the run and that is at the smoke shelf - but is it not extreme by any stretch of the imagination. I have noticed that they have pre-insulated liners at woodland direct that look pretty slick and seem like they may be easier to get down the flue - would these be the way to go. My other question is should I even bother with insulation on an internal chimney like this - my instinct says yes but I dont want to buy expensive insulation only to not be able to get it down the flue and have to rip it off in the end.

Any suggestions for my situation would be appreciated

 

[bholler]

Yes you need to have it insulated unless you have the required 2" of clearance from the outside of the masonry chimney structure to any combustible material. And no an insulated 6" round liner will not fit down a 7 by 11 flue. You have a few options. You can go with a 5.5" insulated liner if lopi says your insert will run ok with it at that height. You can use an ovalized 6" liner which capacity wise will equal about 5.5" . An ovalized 7" liner which will get you up to a 6" round capacity. You can have those old liners broken out so you can fit a regular 6" round insulated liner. Or a duraliner rigid preinsulted liner may work with a flex section on the bottom as long as the rest is very straight. But i would strongly recommend against the double wall flex liner. A heavy flex liner is far superior to those and is still smooth wall (that is what we use for all of our wood stove installs) but a regular old light wall liner will work ok and will hold up better than the double wall stuff. Although not as well as the heavy wall.

 

[webby3650]

Yes you need to have it insulated unless you have the required 2" of clearance from the outside of the masonry chimney structure to any combustible material. And no an insulated 6" round liner will not fit down a 7 by 11 flue. You have a few options. You can go with a 5.5" insulated liner if lopi says your insert will run ok with it at that height. You can use an ovalized 6" liner which capacity wise will equal about 5.5" . An ovalized 7" liner which will get you up to a 6" round capacity. You can have those old liners broken out so you can fit a regular 6" round insulated liner. Or a duraliner rigid preinsulted liner may work with a flex section on the bottom as long as the rest is very straight. But i would strongly recommend against the double wall flex liner. A heavy flex liner is far superior to those and is still smooth wall (that is what we use for all of our wood stove installs) but a regular old light wall liner will work ok and will hold up better than the double wall stuff. Although not as well as the heavy wall.

Have you seen issues that are unique to the double wall liner? I've never used it, just curious.

 

[bholler]

ave you seen issues that are unique to the double wall liner? I've never used it, just curious.

the inner layer is very thin and unsupported on the bottom edge. It snags easily when cleaned. If you bend it a little to hard that inner liner buckles and then sticks out and that absolutely gets snagged. I just really don't see that it is very durable at all

 

[webby3650]

the inner layer is very thin and unsupported on the bottom edge. It snags easily when cleaned. If you bend it a little to hard that inner liner buckles and then sticks out and that absolutely gets snagged. I just really don't see that it is very durable at all

Sounds pretty junky!

 

[BrotherBart]

Yep. Why I trashed mine after one season and went back in with single wall liner. All of those "pooched" places are just creosote traps. A lot of money to toss off the roof into the woods.

 

[webby3650]

Yep. Why I trashed mine after one season and went back in with single wall liner. All of those "pooched" places are just creosote traps. A lot of money to toss off the roof into the woods.

Dang! That sucks! I'm glad I've managed to avoid the stuff.

 

[tdibiasio]

Bholler- thanks for the fast reply to my question. I have a follow on question now if you don't mind - is there a definitive way to determine if I have the 2" to combustible distance. This is a three flue chimney with a oil furnace flue on one side and an unused flue on the other, wood insert will use the center flue. So on the left and right sides I should be fine, is there an easy way to evaluate the rest to determine if I need insulation on the liner at all. The block chimney is not exposed on the second floor. Essentially the 3 flues are surrounded by cinder blocks and the fireplace hearth area is stone, but only on the first floor - the rest of the block chimney on the second floor is not exposed and there is no attic. How would you evaluate this?

 

[bholler]

How would you evaluate this?

Well chances are you don't have proper clearances very few actually do. And if it is internal and inaccessible no there is no easy way to check which is why i always assume there is not proper clearance. One place you can see and is never right is the roof. If it is shingle there should be 2" between the shingles and the chimney and that gap bridged with flashing. I have yet to see one done correctly. So basically to be safe you should insulate it.

 

[webby3650]

Well chances are you don't have proper clearances very few actually do. And if it is internal and inaccessible no there is no easy way to check which is why i always assume there is not proper clearance. One place you can see and is never right is the roof. If it is shingle there should be 2" between the shingles and the chimney and that gap bridged with flashing. I have yet to see one done correctly. So basically to be safe you should insulate it.

I agree, I've never seen one with proper 2" clearance. I have seen houses partially burned down after a flue fire that had no clearance though. It may seem like no big deal until you have a flue fire, that'll change your mind quick!

 

[tdibiasio]

Ok now I see that Rockford Chimney supply has a wide selection of oval or rectangle liners and they actually have a calculator to determine the right size to order. When I put in a 6" collar size and 7x11 flue size - the recommended oval liner size was 5"x8.15 which they claim in ovalized from a 6.5" round flex pipe. So if I get the 1/2" insulation blanket around this it may be tight but seems from simple math that it should fit?? This is a more expensive option but I am assuming it is the safer way to go? The numbers were a little different then what was suggested here but I assume the calculator on their site could be trusted?

Does anyone see any concerns with this new plan?

 

[bholler]

The numbers were a little different then what was suggested here but I assume the calculator on their site could be trusted?

My supplier doesn't have 6.5" so we go up to 7" but 6.5" ovalized should be fine

 

[Jo191145]

Well chances are you don't have proper clearances very few actually do. And if it is internal and inaccessible no there is no easy way to check which is why i always assume there is not proper clearance. One place you can see and is never right is the roof. If it is shingle there should be 2" between the shingles and the chimney and that gap bridged with flashing. I have yet to see one done correctly. So basically to be safe you should insulate it.

It's been a long time since I've perused the code books but back in the day masonry chimneys required a 2" clearance from framing and vertical walls. Horizontal sheathing such as floors and roofs were allowed a 1/2" clearance along with trim work which could be fitted tight.
Your right that it would be hard to find a chimney with a straight 2" gap all the way up through the house. I've done just one such fireplace in my life. It was a large pavilion with an outdoor fireplace. The roof was so shaky compared to normal construction I devised an interlocking moveable flashing system that allowed the roof to move freely.