Block off plate and insulation. Necessary or not?

[Spaceman]

I had a Supreme Lumis insert installed and my installer said that a block off plate is not necessary. He is WETT certified and has installed hundreds of inserts and says he never does it. Claims that as long as it is sealed at the top, which it is, there is no air flow, so no need. I was surprised as I thought that common practice is to put insulation above the insert and a block off plate to seal the chimney above the insert. In doing so, it will deflect more heat into the room and not up the chimney. Maybe that difference is incremental. Also I read that it may not be a bad thing t have more heat warm the liner, but the other thing is about whether cold air from the chimney will seep into the room when the insert is not in use. It is installed flush, so no big open space, but there are air vents of course.

My chimney is brick and on the outside and my liner is insulated. Also, I am in Vancouver which does get cold, but nothing like eastern cities.

 

[begreen]

With all due respect to the installer, a well installed block-off plate makes a big difference in heat output of insert. It keeps the fireplace firebox cavity and thus the insert's convection jacket warmer. Otherwise, a lot of heat is lost through the mass of the chimney. If proper insulation can fit behind the insert, the gain is even better.

 

[Spaceman]

Thanks for your reply. Supreme specifically say not to put any insulation behind or around the insert as it voids the warranty and can cause overheating, so I am really only concerned about the insulation which would be above the block off plate. Besides the heat loss issue, what do you think about the issue of cold air coming into the room when it is not in use? Is that a meaningful concern?

 

[begreen]

In our climate, this is not usually an issue unless there is an open air feed or ash trap inside of the fireplace cavity.

 

[stoveliker]

With an outside chimney I would put a block off plate in for sure.
Insulation is tricky given the warranty.