Where is my heat going?

[EbS-P]

A mostly sealed and insulated blockoff plate was very noticeable in my heat output and wood consumption. Even with an interior chimney.

I went up into the attic on a cold ish day. The bricks up there were over 90 degrees. That heat wasn’t making into the house.

 

[NickW]

I agree with those saying to insulate, install a block off, and check your seal; but I will also tell you I just installed a damper on my NC30 and am quite pleased with the results. I replaced the standard stove adapter with one that has a damper in it. Much more controlled burn, healthier fire, longer burns, better heat in the house... Used to run flue temps over 800 for stt of 550-600 air fully shut secondaries only and sometimes couldn't control it, now on a full load I can run flue temp of 700 with stt of 600.

 

[Garbanzo62]

So when I bought my Insert, I told the dealer I wanted a block off plate installed. He said it was not necessary. I have noticed my exterior chimney bricks getting up to about 75 degrees. I am hoping that they can come out and install one when I have the insert serviced. However, if I have to do this myself How well do I need to get that sealed? I am thinking I might need to make this out of 2 pieces of sheet metal to get around the liner without having to dis-assemble everything.

 

[mellow]

I’ve considered it, but honestly, I have zero complaints about heat output. My regency heats my 1800 square feet house with no problems at all.

I get it, not something you want to tackle, but remember you have the summer coming up to atleast do yourself a favor and pull the surround and have a look. Plenty of threads on here on installing a block off plate and my thread on insulating your fireplace.

Pictures sometimes help to visualize what is happening to your wasted heat, check out this post: https://www.hearth.com/talk/threads/finally-got-around-to-insulating-my-fireplace.75755/post-1842157

 

[NickW]

So when I bought my Insert, I told the dealer I wanted a block off plate installed. He said it was not necessary. I have noticed my exterior chimney bricks getting up to about 75 degrees. I am hoping that they can come out and install one when I have the insert serviced. However, if I have to do this myself How well do I need to get that sealed? I am thinking I might need to make this out of 2 pieces of sheet metal to get around the liner without having to dis-assemble everything.

Whatever you do will help, but the better sealed it is the more it will help... Any heat going up between the liner and masonry is lost heat.

 

[stoveliker]

Silicone is your friend to block air flow. And insulation to block heat flow.
So a metal plate with insulation on top, screwed into the masonry, and with a generous (!) bead of silicone - is I think the way to go.

Two halves may indeed be best. (More silicone at the seam...)

 

[Garbanzo62]

I'm not sure I want to screw into the masonry. I wasn't here for the installation, but I think that they only took out the original damper plate (they left that). So I am thinking I can put two metal pieces on top of where that damper plate sat and use machine screws to connect the plate to those. Effectively the old damper sill will be sandwiched between the metal strips and the plate. As far as the two piece plate, I am thinking I could have them overlap and then machine screw them together to create a tighter fit.

 

[begreen]

I'm not sure I want to screw into the masonry. I wasn't here for the installation, but I think that they only took out the original damper plate (they left that). So I am thinking I can put two metal pieces on top of where that damper plate sat and use machine screws to connect the plate to those. Effectively the old damper sill will be sandwiched between the metal strips and the plate. As far as the two piece plate, I am thinking I could have them overlap and then machine screw them together to create a tighter fit.

Brick is soft. Setting some tapcons is not a big deal with a small masonry bit. A better seal can be achieved with a screw flange that can be caulked with silicone. Predrill the screw holes to clear the screws, then put the BO plate up in place. Mark the hole locations on the brick with a black sharpie. Remove the BO plate, drill the holes to the right size for the tapcons, and put the plate back up, screw it in place.

 

[Highbeam]

A mostly sealed and insulated blockoff plate was very noticeable in my heat output and wood consumption. Even with an interior chimney.

I went up into the attic on a cold ish day. The bricks up there were over 90 degrees. That heat wasn’t making into the house.

But that hot liner is still in the masonry chimney heating it up. How does sealing the bottom with a blockoff plate stop that? I look at an open bottom chimney (no BO plate but a sealed top plate) as a bell being put in the water. The air in the chimney is trapped, though hot, whether the bottom is sealed or not.

Proof is in the pudding I guess but I never understood why the bottom plate matters if the top is sealed.

 

[stoveliker]

I think block off plates make most sense (for heating efficiency) for insulated liners. Sure they'll still leak heat, but not as much.
At that point the heat input into the chimney from the insert may be the larger fraction?

On the other hand, block off plates do work well for times when the fire is not burning: no cold air falling down (no "bell in water" effect for cold air).

 

[mellow]

If we are talking about inserts we are talking about making a sealed envelope for that insert all the way around but not touching (best way if you ask me), the heat will stay in one place and therefore be more efficient since the fans will be able to wick that heat off and push it into the living space, not lost into the masonry and up the chimney.

 

[bholler]

But that hot liner is still in the masonry chimney heating it up. How does sealing the bottom with a blockoff plate stop that? I look at an open bottom chimney (no BO plate but a sealed top plate) as a bell being put in the water. The air in the chimney is trapped, though hot, whether the bottom is sealed or not.

Proof is in the pudding I guess but I never understood why the bottom plate matters if the top is sealed.

Because the hot air rises. The heat then transfers into the masonry and is lost to outside and the cooler air drops. Yes it's not just a clear path to outside but still can add up to allot of lost heat.

 

[EbS-P]

But that hot liner is still in the masonry chimney heating it up. How does sealing the bottom with a blockoff plate stop that? I look at an open bottom chimney (no BO plate but a sealed top plate) as a bell being put in the water. The air in the chimney is trapped, though hot, whether the bottom is sealed or not.

Proof is in the pudding I guess but I never understood why the bottom plate matters if the top is sealed.

My stove sits completely in the fireplace. All the estimated heat went up into the chimney then all the convection. It has a large smoke shelf. I can stand up in it. 12x12 clay liner left plenty of room even with an insulated 6” flex liner.

 

[mellow]

My ultimate setup was the BK in the insulated fireplace burning low and slow connected to an insulated liner, all the heat was trapped in the fireplace and was expelled by the fans on the insert but the liner still kept warm due to the insulation and still had a good draft despite the lower exhaust temps from burning low. I could go low and slow for extended periods of time but still keep the house in the mid 70's on the coldest of days.