Reduced clearance issue.

[HJsimpson]

Ok i am trying to make heads or tails of the NFPA standard 90B code about reducing clearance to combustibles. I have hung 1/2 durock on
cieling spaced 1 1/2 inch off joist but dont know if is concidered insulated material or if i need something behind it. The clearance says 18" for top of plenum but wth proper material i can reduce to 9".With current setup i have 12" space between durock and plenum. Any help what i should do would
be greatly appreciated.

 

[begreen]

From what you have described it sounds like you are well covered for safety. But just to be sure, if you can post a picture or sketch, that would be great.

 

[HJsimpson]

Here are some pics. I have four 3 X 5 sheets up. There is 19" from top of flue to Durock so im okay there. I used 3 1/2 screws with 2" fender washers to attach with 1/2" conduit for spacers.

 

[begreen]

That helps. What is being installed, a wood add-on furnace? Is the duct on the right the supply plenum? It looks like it is right up against the durock. Also, what is the pipe or round opening at the back center, right under the edge of the durock?

 

[laynes69]

Could you post some pics of the overall area? The main furnace and ducting. It looks to me you may have some clearance issues in the ductwork. Also I know the manufacturer says is okay to operate the furnace if power goes out, but realize it's only if the ductwork is setup for gravity. Otherwise you should take caution if this happens. That's where the importance of duct clearances is.

 

[HJsimpson]

Yes that is the old cold air return agaisnt the board and the round pipe at top in the back is for a floor register which will be removed. Most of the duct work is being removed and rerouted
to be 18" below joist for first 6' then 2'' from there on per code.
laynes, I know they say its okay to operate without power but im not comfortable with that which is why we purchased a generator with automatic transfer switch. Besides my luck power will go out just after i loaded it up and went to bed.

 

[laynes69]

Very good, sounds like you are on track.

 

[begreen]

Looks like you are doing things right. Keep taking shots. It looks like an interesting install.

 

[pen]

Nice to see someone wanting to do it right, no matter how frustrating it may be. Well done!

pen