insulating masonry chimney

[bjwme]

hey guys got another chimney question. I have a double flue masonry chimney that goes through my attic.It has a clay liner and in toal is about 26 feet. About six to seven feet of the chimney is in the attic and that is were I start to see build up in the coldest months. I see temperatures well below zero in the winter and I was wondering if it would be a good idea to insulate that part of the chimney in the attic. If so what would be the best/up to code way to do that. I have had a few people tell me just to wrap it with rock wool, which would be easy and others say to frame it out and leave an air gap between the chimney and the insulation. I am not sure about wrapping it with rock wool even though it is fire retardent, the couple of friends who told me to do that said i shouldnt have any troubles even if i had a chimey fire because the chimney is brand new and built to code. What do you guys think?

Thanks for the help

 

[hayrack]

Leave an air gap. You never put anything up against a chimney. If you are burning seasoned wood you won't have problems

 

[Gooserider]

Leave an air gap... Required by code, because BAD THINGS (TM) happen to people that didn't!

If you have the space, consider putting in an insulated SS liner w/ top and bottom blockoff plates as needed by the install... If you have space for the liner, but no insulation, do the liner and pour vermiculite into the gap between the liner and tile. This won't be as good as an insulated liner, but it will help.

Putting an insulated liner in does two things, both good... First it obviously insulates the smoke passage. Secondly, because it reduces the flue diameter, the velocity of the gases in the flue will go up, giving them less time to cool and condense on the walls of the liner.

Also, depending on just what the sizes of the appliance and the clay liner are, and whether or not it's an outside chimney, you may not have an optimal flue size, and could even be outside of code specs. A liner will give you the optimum flue cross section, and make sure you meet code.

Gooserider