Chimney Liner Block Off Plate

Without one the flue liner which should be insulated and the stove will try to heat the mass of masonry that is exposed to the outdoors.

Chimney liner block off plate.

This opening will vary in size but generally you will be installing a 6 or 8 chimney liner. If you have an internal chimney then insulation is better but you could get away with a good block off plate and stuffing some mineral wool down a couple of feet from the top. Top plates and caps can be ordered through most liner companies. Stagnant air is a pretty good insulation.

This will prevent any airflow through the area around the liner. A block off plate is particularly helpful with inserts installed in fireplace on exterior walls with exterior chimneys. When you have such a large opening around the liner a large amount of the hot air generated from the wood stove will be rising up into the chimney cavity. Heavy aluminum 26 or 24 ga sheet metal both work.

This can result in a significant cooling of the stove and large heat loss. It is very common to have to ovalize a short section of the liner in order to pass the liner through the throat damper. To prevent this from happening install a block off plate. The block off plate is a horizontal plate that blocks off the opening where normally a damper is in a fireplace.

The block off plate is a fail for now we could not get the liner off the flue collar at the insert level in order to get the insert free we would have had to setup a ladder and climb the chimney about 35ft off the ground grade is 10ft below fireplace chimney is about 25ft and disconnect the liner at the top and lift it off i personally.