How To Insulate a Flue Opening w/4" Flex Liner

[fireitup]

I'm about to vent a 4x30 flex liner up (or down if you prefer) a 200yr old masonry chimney. Was told by more than one person that insulating the "open flue" around the 4" liner would be a very good idea. I don't expect detailed instructions here in a thread, but does anyone have any basic suggestions as to how to do this? Do they make kits for this? Any videos available for self-fabrication? Thanks guys!

 

[Chrisnow86]

if your chimney is in good shape just run the liner as it.. it should work fine without being insulated. center chimney of outside exposed?

 

[fireitup]

200yr old house. Central staircase, fireplace either side go up and join together into one center chimney. Are you asking if the side of the chimney is exposed? (on the side of the house)...no. 2 flues into one chimney. The living room hearth/flue is venting my Burnham boiler. The dining room hearth/flue will be venting an insert.

 

[Chrisnow86]

with the chimney in the center i would just run the liner and not insulate it.. that pipe will be from 90 to 120 degrees or so.. just run the liner and see what happens.. the gasses wont cool off and condense.. and hey if it warms the chimney thats extra heat

 

[fireitup]

So if my 4" diameter liner goes up into an open flue mouth that's approx. 10x16, I won't get tons of draft or cold air coming down the chimney back to the insert?

 

[Chrisnow86]

is it running all they way to the top? with flex pipe kits there is a cap that goes on top.. in fireplace installs they put a steel peace at the bottom of the flue to keep it air tight so you dont get cool air coming down into the house

 

[briansol]

Your cap should fill the 'perimeter' leaving the extra padding in the chimney blocked off at the cap, other than the 4" hole.

 

[alternativeheat]

I'm about to vent a 4x30 flex liner up (or down if you prefer) a 200yr old masonry chimney. Was told by more than one person that insulating the "open flue" around the 4" liner would be a very good idea. I don't expect detailed instructions here in a thread, but does anyone have any basic suggestions as to how to do this? Do they make kits for this? Any videos available for self-fabrication? Thanks guys!

I think you will find pretty much all of us who have run liner down pretty tall chimneys just insulated over the old smoke shelf and capped the top of the chimney. I ran 26' that way in an old brick chimney, works fine. Thats assuming the install is into a fireplace. You can find videos where they wrap the entire liner with insulation but I haven't heard of much of anyone doing that in practice. I spoke with two different local installers here and neither insulates liners going in a masonry chimney.

 

[fireitup]

I will be installing a SS chase cap at the liner's termination. I'll use hi-heat RTV, etc. to seal everything up there. Then there's a SS cap that goes on top of that. So you guys think a properly installed chase cap will be adequate?

 

[Chrisnow86]

ya.. run it!

 

[ttdberg]

The 4" flue will go through a block-off plate at the top. You will have to buy or make your own block-off plate using a sheet of SS and apply it using liberal silicone to make it air tight. That will stop draft from coming down or heat escaping up. You can insulate at the very top and bottom as well, but it's not necessary if your flue is not on an outside wall.

 

[fireitup]

I like what you guys are telling me...thanks!

 

[Caleb Joens]

I capped the top and insulated the bottom with roxule. I was told you don't want to insulate the top because when you are not running the stove your chimney will have a large temperature gradient because part of it is exposed to outside and you risk condensation where the cold meets the hot. It makes sense, but i'm not sure how often it becomes a real issue.

 

[alternativeheat]

I capped the top and insulated the bottom with roxule. I was told you don't want to insulate the top because when you are not running the stove your chimney will have a large temperature gradient because part of it is exposed to outside and you risk condensation where the cold meets the hot. It makes sense, but i'm not sure how often it becomes a real issue.

I just insulated the bottom as well.

 

[fireitup]

Thanks all for your comments. I'll do a bang up job up top with the chase cap, and maybe insulate a little down at the flue shelf. I'll let you guys know how I make out, early next week hopefully!

 

[tech tchr]

I insulated the top by stuffing 4' long bats of Roxul on both sides of the flex pipe. Chimney was 12x16. Then used a cap to seal the top. I stuffed insulation around the bottom also around the damper. Then siliconed a T to the pipe.