Expert: James Ball - 12/4/2010

Question
Hi James,

I'm replacing a Buck 27000 slammer with a new insert (sweep found flue liners cracked last year#.  I've got a masonry fireplace with a heatilator firebox. I'm planning on installing an insulated liner from the insert to the top of the chimney.  Here's my questions:
1. The existing mortar between the steel firebox and the facing brickwork is virtually non-existent.  My local sweep said that the thermal profiles between the firebox and brick is rough on mortar, and said I could get away with using insulation #either fiberglass or ceramic wool)stuffed into the gaps.  Is this a viable fix?  Are you aware of any mortar products that are more forgiving to temperature differentials between brick and steel?
2. The instructions for the insert recommend installing a plate in the throat area to keep air out of the chimney, affixing it with masonry screws.  Since I've got a steel firebox, do I really want to drill holes through it?  Can I use furnace cement to attach angled steel to the walls of the throat, then screw the sheet metal to the angled steel?
3.  Is it okay to block off the existing ducts for the heatilator?  Cold air pours out of them if they're not covered.

Thank you for your time.

Answer
Hello Sean, 1) yes you can use either insulation
2) furnace cement would not hold up, they make a kit for that area or you can just stuff with insulation (non paper backed or ceramic wool)
3) yes you can "block off" the vents maybe a magnetic sheet like they use on trucks for advertising? so you can remove when using the stove to get  bit more heat
4) I would have a local Certified Chimney Sweep www.csia.org, (there you can look up by zip code to find one near you) take a first hand look at what you have, they should be able to help.
you seem to have all your bases covered, nice to see a  home owner doing it the right way
Hope this helps
James