Do I need to block off the bottom of flue after insert reline?

[btuser]

I installed a new insert in an existing masonary chimney. Its an exterior chimney so I insulated and sealed the top of the flue with a top plate, sealed with HT silicone ect. There's no draft sneaking past it. The insert has a surrond that completely blocks off the old hearth so nothing is visible. I'm done. I'm happy. It heats like the dickens.

However, after investigating everyone else's installs I'm left feeling insecure. Was I supposed to block off the bottom of the flue? I could see if it was a large hearth and it was visible, or if you weren't going to seal the top or insulate the liner and wanted to prevent the liner from heating the air and creating a convection current. But is there anothe reason I'm missing? Please help me with my installation envy. Let me know its ok before I start ripping things apart again.

 

[Bone1099]

Is your insert flue directly connected to the masonry chimney? if not then any small leak around your insert cover plating is a draft leak. im not sure what you mean by sealing and insulating the top of your chimney if it is masonry. please elaborate.

 

[btuser]

Is your insert flue directly connected to the masonry chimney? if not then any small leak around your insert cover plating is a draft leak. im not sure what you mean by sealing and insulating the top of your chimney if it is masonry. please elaborate.

Not the top, the bottom. There is a sealed top plate at the top of the liner but the at the bottom (where the damper was) its just the liner coming down. I didn't bother to seal the bottom of the chimney where the liner comes out to connect to the insert. There's no draft at all at the bottom, I'm just second-guessing myself now that I've seen other installations.

 

[Tendencies]

I sealed mine at the bottom to keep the heat coming off the sides and back from going up alongside the flex.

 

[btuser]

How long/large is your chimney? I have a 6" ovalized, insulated liner inside a 8x8 tiled flue. Not much room to spare. There may be a couple cubic foot of air space between top and bottom but if that's all there is to worry about I'm all set.

Maybe to keep the cold flue air from rolling down in a convection pattern during non-burn times? Still, pretty small potatos. I'm going to have to check it with a infra-red thermometer this Winter, but last year I compared the temps around the stove pre-burn and during and found no cold spots or hot spots.

 

[ddddddden]

I sealed mine at the bottom to keep the heat coming off the sides and back[of the stove] from going up alongside the flex.

That's the main reason, BT. If you are happy with the amount of heat in your house, you are good to go, AFAIK. Of course, you may not know until January if you are truly happy with the amount of heat in your house. . .even though you have sealed the top of the chimney, an external chimney will still conduct heat to the outside air. It acts like a big heat sink, so people like to seal it off from the living area. The best technique includes insulation behind the blocking plate, also not a bad idea for the top plate. Some insulate the inside of the fireplace too. Do *you* need to do all this? The only way to know for sure is to try it like it is in winter. Given the PITA of R&R an insert, I'd let it ride until summer. Worst case, after a taste of winter, you decide you are losing too much heat and do the R&R on a warmish weekend.

 

[ddddddden]

. . .Some skip the plate and just stuff the damper area with rockwool. I'm not sure how effective this is vs. insulation with a plate, but if you need to to a quickie R&R on a January afternoon, it might be the ticket. It seems like it can be a PITA to get a plate to fit well, and it may take a few tries with the metalworking.

 

[Jags]

What is STOPPING you from installing a block off plate?? There is NO downside, only upside. If you have even raised the question (which you have) JUST DO IT.

***now where is that key for the Nike "swoosh"*** Ahhh....there it is...

 

[btuser]

What is STOPPING you from installing a block off plate?? .

That's work for the sake of work. All set with that. I could see the point of a plate if it were a stove in the hearth, but as far as an insert w/ surround I think its a relic from direct-connect installations when stoves/inserts liners stopped after clearing the damper in an old fireplace.

Right now its 50 degrees outside and I haven't fired my stove in almost 24 hours. My exterior walls are 68-70 degrees. My insert is 70 degrees as well as the surround. I have no doubt there is a heat loss associated with the masonary but if it was considerable the thin metal of the surround would show a difference. The fact that its the same temp as the room tells me its very small. I'll have to check the temp of the surround when the stove is lit to see if there's a big jump which would tell me there's heat hidden behind it. I never run the insert without a fan, and the box inside a box keeps the backside of the stove much lower.

Even though the line is insulated it's still going to radiate heat into the tiled flue cavity and eventually equalizing out any effect of heat radiating up the chimney. Yah, that's my story and I'm sticking to it.

 

[Jags]

You started it:

....after investigating everyone else's installs I'm left feeling insecure.

You answered it:

I have no doubt there is a heat loss associated with the masonary....

You justified it:

That's work for the sake of work. All set with that. I could see the point of a plate if it were a stove in the hearth, but as far as an insert w/ surround I think its a relic from direct-connect installations.........Yah, that's my story and I'm sticking to it.

I'm just here to listen. :lol:

 

[Rudyjr]

There are many cases of people that have posted on this forum unhappy with the heat output from their stoves due to the lack of a block off plate. It is really not that difficult to do all things considered, but you need some mechanical skill to do it yourself. If you are happy with the heat output of your stove without one you may be good to go, but you are certainly losing some heat to the chimney. In my install with an exterior chimney it most certainly made a huge difference in heat output versus just sealing the top.

 

[golfandwoodnut]

I had mine professionally installed (I sure think it was professional) and they did not put in a block off plate. I questioned it and they said it was sealed at the top and would really not make a difference. It is my first year and seems to be heating fine, and I know it is a PITA to remove. The Jotul cast iron plates are very difficult to get on just right. I think I am going to wait and see if I have any issues before I mess with it.

 

[btuser]

I'm very happy with the heat output from the insert when the fan is running, nosomuch with the fan not running. I'd guess 90% of the heat I'm gaining is through fan convection and not radidation. I'm going to resist the urge to start a fire tonight and check the surround/stove temp via infra-red themometer tomorrow morning. If there's a slight differential I'll know I'm all set. If there's a large one I'll know there's some heat to be salvalged.

 

[btuser]

Ok, this morning temps:

Outside temp - 52
Inside room temp - 67
Stove temp - 66 outside, 62 if I point the thermometer at the bypass.
Surround temp - 67 to 66.
Exterior wall temp 67

No block off plate needed at 52 degrees. Odds are my stove is going to be firing any colder than this so I'll have to check temps tomorrow.

 

[btuser]

In case anyone is interested I've come to the conclusion that a block off plate would not be worth the effort in my case/installation. I've taken a couple weeks worth or readings, intentionally letting my stove go cold for 24-36 hours a few times (not easy, very tempting) and come to the conclusion my stove is naturally warm. It gives off heat without wood. More exactly, the flue shares a wall of the chimney with the furnace. That exterior wall of the chimney is actually warmer by as much as 3 degrees, and I find the surround to my stove hitting 71 while the surrounding walls/surfaces are at 68-70 degrees. The inside of the stove is cooler, but the outside box of the insert is still 70 degrees, warmer sometimes on the right by 1-2 degrees (the side it shares with the oil boiler. I think this is only going to matter in the very mild shoulder seasons, whereas during the heating season I'll be the one warming the chimney for the boiler.