Adding Terracotta Flue Height

[factfinder]

Good evening,

I have a couple of questions concerning extending an unused flush-to-crown terracotta liner about 12".

I currently have (3) 13x13 terracotta flues, one unused, and other two for fireplaces. The two for fp's extend about 8-12" above crown and capped. The unused was built flush to crown. The unused flue will be used as a chase for an SS flex liner for an oil boiler.

The following questions concern high wind, freeze/thaw/water penetration, draft/backdraft, and best practices:

1) Do I need to extend the terracotta to match the other flues, for either draft, or SS liner top plate connection purposes? Can I just mount the top plate and cap to the Crown (w/silicone or mortar) without the problems listed above?

2) If I need the small extension, can I attach to existing teracotta with high temp, all weather silicone, along with top plate/cap/flex liner? If not, can it be done with mortar instead of silicone? If not, any other "easy" ideas?

Thanks for your time and help.

 

[summit]

mounting both the same level should not be a problem (as long as there are not negative pressure issues in the house, in which case, you got more issues than your flue). otherwise, pm Craig and ask for the extenda flue.

 

[factfinder]

Thanks.

Does anyone know if HTV Silicone is a good enough adhesive for joining the small terracotta extension to the existing terracotta flue?