For flue pipe on oil fired boilers, when refering to Minimum Installation Clearances To Combustible Materials, what material is NOT combustible for the purposes of this requirement?
To be more clear, what material can be used that will allow closer installation than typical 18 inches? Cement board (Durock type brand)? Sheet metal (what thickness)?
I know the info is in NFPA 31, but I do not have that book.
Replies
Odds are, your cement board attaching points will be framed with combustible materials. You could use steel studs.
You really need to contact someone in your municipality and ask them that question. Maybe they will allow double 1" type X drywall and closer clearances.
There are different types of prefabricated UL listed chimney that have different clearance requirements. Hart and Cooley has a double wall stainless steel flue pipe with a ceramic material between the flue walls. Two inch clearance to combustibles, rated for over 1000*F, special purpose roof penetrations and floor supports, heavy and quite expensive. Not rated for positive pressure applications, though. Special order around here, but easily accessible.
Other companies make pipe rated for positive pressure applications and things like grease duct. I've never worked with prefab grease duct, but the positive pressure boiler flue was a real PITA. Sealant, v groove bands for the pipe flanges- inner and outer layers....