Clydesdale Insert Not Happy with its performance Please help !!!!

[LeonMSPT]

Installers in this area, my own, and two others I've done, are definitely sealed at the top of the chimney. Stainless chimney liner, with an insulated second layer of stainless pipe lined with 1/2 insulation, taped at the seams. Then 1/2 inch blanket insulation, taped at the seams, with a steel mesh to protect it when it's horsed into the chimney. The insulated layer ends at the top of the flu, chimney pipe continues up another 6 inches to a foot.

A stainless plate just fits over the chimney pipe. It is "pitched" around the hole in the center so water will not run into the gap if any should make its way in there. Before this is put on, high temp silicone caulking compound is liberally applied to the chimney top, and the plate is set on this.

All the connections are completed between the liner and the insert before this step.

A helper lifts the liner up slightly from the top, just taking a strain on it and maybe lifting about an inch or two, "take the slack out of it.", and holds it.

Push the top plate down on the caulking compound and the chimney, sealing that joint. Immediately apply a bead to the joint between the top plate and chimney pipe, and the bottom of the inclined "collar" with the clamp in it.

Add the "collar" with the clamp in it, and tighten it. Once it is tightened, helper can let go. Then caulk around the seam between the collar and the pipe.

Airtight, watertight, no leaks. There is a little "tension" in the liner, which will lessen the effects of expansion and contraction because it has more freedom of movement than if it was sitting full weight on top of the insert and clamped there.

It's what most are doing now, and seems to be working. Might be some out there not sealing things up well at the top, allowing air travel through the chimney to the outside. These situations should absolutely put a block off plate in.

 

[Rudyjr]

Leon, This has come up before about where does the heat go if the top of the chimney is sealed. If you look at the link in my signature you will see photos of my install. The block off plate in my install is at the point where the firebox is straight where it starts to taper to the damper. When my stove is up to temperature the brick is very warm to the touch up to where the block off plate sits. I have an exterior, below grade fireplace with a full wall masonry fireplace above it. If this was not blocked off I would be trying to heat everything above that stove up, while the outside was trying to cool it down, a massive amount of heat would be lost to that mass. After many hours of burning the temperature does go up on the brick wall above my stove due to the heat in the room from the stove.

 

[oconnor]

So where does the heat go when no block off plate is installed?

I'm not sure myself. As Rudyjr mentioned, I have a rockwool plug in my damper (plan on pulling it out and installing a block off plate soon). My thoughts are like this:

Chimneys are not airtight structures - they have cracks, and are made from pourous materials. Many chimneys have other appliances in them in adjacent flues, and those appliances are not airtight either.
Convective currents will build around the flue and cool it - with a constant supply of fresh air, more cooling will occur. Plate will reduce the frsh air supply
Block off plate gives a mechanical form in the fireplace to encourage convective circulation back into the room.

As for an airtight seal at the chimney top, I doubt it can be done well enough to last long. High temp silicone won't take the heat of a wood fired flue (1000-1200*F), and stove cement isn't meant for outdoor exposure. That, and the amount of heated bouyant air around the 1200*F stainless pipe that is heating the space inside the chimney is going to get out any hole it can, like the small gap where my flex liner comes thru the top plate - not air tight, and never will be without sealing it every few months. And then there is the clean out, (mine in the basement is stove cemented shut)

I'm not certain that block off plates are the holy grail, but they do seem to work well by all reports, and are not difficult, just tedious. I promise to install one once my installer gets back here to fix my liner instal so it meets code (uninsulated liner in a 75 year old brick chimney with no clearances to combustibles = code violation and hot walls, but he is WETT certified, so he must be right.....NOT!)

 

[LeonMSPT]

My own is an interior chimney, 35 ft tall. Hadn't considered heat loss from conduction in an exterior chimney, but do see where that could be a major issue with an exterior chimney. I've cleaned all three, my own and the two I did. I've even ripped one apart because I wasn't happy with the length of the pipe sticking out. I'd left a foot and a half, the last four feet was cruddy and the rest clean. Suspected the foot and a half was acting like a wick, drawing heat out of the upper part of the chimney. Seems the cap is remaining cleaner than it was with 6 inches instead of 18 sticking up.

It was air and watertight... and high temperatures didn't affect the silicone at all, fact is it was still pliable and even a little sticky after a year. Took more time to rip it apart and clean it off than it did to clean the chimney and put it back together.

So,"I see, said the blind carpenter to his deaf dog, as he picked up his hammer and saw." I get an outside chimney siphoning heat from the home. That would be true if the home owner blocked the chimney off above and never used it for anything.

We all do tend to think "ours'" is like "everyones'"...

Interesting discussion though, and thanks for answering.

 

[Rudyjr]

Brent, When you are in the process of getting your liner issue fixed how about doing an experiment? Pull the rockwool out the night before and document what kind of performance differences your stove exhibits, temperature differences of stove and adjoining rooms. It appears from your pictures that you have an interior chimney so it should be very interesting how much loss there is, I am willing to bet it is considerable. Maybe this will be of benefit to those that do not think that they will be helped by installing a block off.