Liner Insulation

[Keith Wheat]

Our installer is offering either a fully pre-wrapped or a totally bare single wall 6" 316 stainless steel flex liner through our interior masonry chimney to serve a new Lopi Large Flush Hybrid Insert.

Neither of those options seems perfect to me. My ideal is an unwrapped liner from the appliance to just a few feet below the roof line, then insulation around the segment of liner that extends through the roof up to the top of the chimney. I figure that the uninsulated, lower segment will offer the possibility of heat transfer into the house while the insulation on the top segment will reduce creosote condensation in that part of the liner that is likely to be coolest and where heat will not transfer into the house.

The installer has made no offer of a block-off plate nor have I requested one. The only plate will be at the top of the chimney.

The top of the chimney is maybe a few inches above 30 feet from the floor of the masonry fire box. There is a gentle offset of less than 2 feet to the left exiting the fire box. I can see the underside of the rain cap with the back of my head on the floor at the left side of the fire box looking up through the square clay tile liner.

What is standard practice regarding insulation for a liner in an interior chimney? Is there a consensus that standard practice could be improved? Uninsulated or totally insulated, neither with a block-off plate, are the only options we are offered. The installer did not resonate with the idea of a lower unwrapped segment and an upper wrapped segment. I am inclined toward the unwrapped liner since it is an interior chimney.

 

[bholler]

Our installer is offering either a fully pre-wrapped or a totally bare single wall 6" 316 stainless steel flex liner through our interior masonry chimney to serve a new Lopi Large Flush Hybrid Insert.

Neither of those options seems perfect to me. My ideal is an unwrapped liner from the appliance to just a few feet below the roof line, then insulation around the segment of liner that extends through the roof up to the top of the chimney. I figure that the uninsulated, lower segment will offer the possibility of heat transfer into the house while the insulation on the top segment will reduce creosote condensation in that part of the liner that is likely to be coolest and where heat will not transfer into the house.

The installer has made no offer of a block-off plate nor have I requested one. The only plate will be at the top of the chimney.

The top of the chimney is maybe a few inches above 30 feet from the floor of the masonry fire box. There is a gentle offset of less than 2 feet to the left exiting the fire box. I can see the underside of the rain cap with the back of my head on the floor at the left side of the fire box looking up through the square clay tile liner.

What is standard practice regarding insulation for a liner in an interior chimney? Is there a consensus that standard practice could be improved? Uninsulated or totally insulated, neither with a block-off plate, are the only options we are offered. The installer did not resonate with the idea of a lower unwrapped segment and an upper wrapped segment. I am inclined toward the unwrapped liner since it is an interior chimney.

Does your chimney have the required 2" clearance from the outside of the masonry to any combustible materials? If not you need full insulation

 

[Keith Wheat]

I do not know if I can check clearances non-destructively. Most of the masonry is enclosed in finished walls.

The house is in Massachusetts and was built around 1986. The masonry chimney column has four clay lined flues including the one that will soon receive a new steel liner. Is it safe to assume anything about clearances based on the date of construction and the original intended use of the flue being for a conventional fireplace?

If nothing can be ascertained about existing clearances, then is the default recommendation always to insulate the liner?

What are the insulation requirements? I do not know much about what the installer is offering other than a liner that is "pre-wrapped."

How will the building inspector verify clearances? Will she or he punch a bunch of holes in the walls?

Should we expect to burn more wood long term with an insulated liner since more heat may exit the house and less heat may migrate through the masonry? I wonder if anyone has any experience from before and after insulating a liner, all else being equal.

 

[bholler]

I do not know if I can check clearances non-destructively. Most of the masonry is enclosed in finished walls.

The house is in Massachusetts and was built around 1986. The masonry chimney column has four clay lined flues including the one that will soon receive a new steel liner. Is it safe to assume anything about clearances based on the date of construction and the original intended use of the flue being for a conventional fireplace?

If nothing can be ascertained about existing clearances, then is the default recommendation always to insulate the liner?

What are the insulation requirements? I do not know much about what the installer is offering other than a liner that is "pre-wrapped."

How will the building inspector verify clearances? Will she or he punch a bunch of holes in the walls?

Should we expect to burn more wood long term with an insulated liner since more heat may exit the house and less heat may migrate through the masonry? I wonder if anyone has any experience from before and after insulating a liner, all else being equal.

It's safe to assume you don't have the required clearances. Hardly any chimneys do even on new construction even though it's clearly required by code.

Pre insulated liners will give you zero clearance to combustibles.

The inspector most likely won't know or care about Chimney clearances

With a modern stove the exhaust temps should be low enough that you don't have much extra heat in the stack to spare. So no you won't use extra wood and you absolutely want a blockoff plate.

With 30' you are going to be over drafting and your installer will need to do something to control that