Vents on furnace & water heater.

Found this on today’s inspection. Furnace installed in 2007. Flue looks funny. Cardboard barrier around furnace flue in attic.

To many 90’s in it for me looks like crap was the furnace gravity or forced air. 1 inch clearance to combustibles on double wall class B vent pipe. I would recommend the card board be removed even if it was a foot away from the flue simply because someone might knock it against the pipe and leave it there. Recommend metal to keep the insulation back from the flue

The water heater vent pipe has a negative or neutral pitch. To ensure a positive draft, it should rise at one-quarter inch per foot.

The draft hood on the water heater is not seated.

If the cardboard is < 1" from the B-vent flue in the attic, or if the flue is < 1" from anything else combustible (cellulose insulation?), then that’s a no no.

Let me ask you this question why should it be considered a combustible hazard on a furnace flue pipe fifteen feet from the furnace where the flue penetrates the roof its still required 1 inch of clearance to combustibles but one can touch the flue pipe with the furnace operating and it will not burn your hand???

I don’t know where you got the “fifteen” number.

Regarding the 1" rule, ask the manufacturers. It’s their standard.

And, I know I’ve accidentally touched furnace flues during an inspection and it certainly did burn my hand (and once my face).

I just made the 15 # up out of my Butt it might be 10 feet makes no difference. The one inch rule is set by the MFG and yes I live by it write up everyone I see. Just asking if you know why if the flue is not hot how can it be a danger there is a reason

Charley, I want to say electrolysis (no not hair removal) is a complex process that makes something more flammable over time. Eventually, the combustion point of a product lowers and it takes less and less to ignite it.

The manufacturers cover their rear end just like home inspectors do. They set standards with plenty of safety factor built in.

Now you are thinking give me the safety factor;-) I have had people ask me that same question if it is not hot why does it have to have clearance. I have a answer for them

You got that part right something can happen over time

Which is why it is an issue.

That is correct but what is the issue. I’m not easy tonight not giving it up:D

Haha. Friggin Charley.:twisted: The issue is the whole clearance thing. Since you’re not giving up, I definitely will. I can’t even tell how far that cardboard is away from the vent. I was just describing a process I heard in school about why things (if within clearances) can be problematic, and the actual process of why that occurs. But I would say a product like cardboard is most unconventional in that application and would raise doubt in my mind, considering its likelihood to combust.

There, I think that satisfies me without challenging you. I hope.

Electrolysis??? There are only 2 definitions of that word, and neither makes sense in relation to your sentence.

  1. Physical Chemistry. the passage of an electric current through an electrolyte with subsequent migration of positively and negatively charged ions to the negative and positive electrodes.
  2. the destruction of hair roots, tumors, etc., by an electric current.


I know.
I gave up trying to find the exact term and went ahead with the post, but I swear it was either electrolysis or something very similar. That’s why I said “I want to say”. If I find it I’ll let you know. I have it somewhere in the bookcase. Maybe Pyrolysis.

We already resolved the clearance issue several post ago I hijacked the thread and asked another question still related to flue pipes. You are correct in your thinking about the paper it obviously becomes dry and brittle absolute moisture content vanishes with heat applied like kiln drying lumber. My question again is why at say the roof penetration for a flue where the pipe is just mildly warm is there a danger of potential combustion. I prefer the thought process I don;t like to just give answers you won’t remember on the next inspection you do.:smiley:

Oh heck, I don’t know. Thought we were on the cardboard. I was off track then, my bad. I suppose you could use the pyrolysis thing for the roof depending on what the clearance is, but thats a reach and looking for something to condemn in my opinion. But hey, codes are written by lawyers representing builders and designers aren’t they? Anything is a risk to them.

(Hands in air backing away slowly towards door)

A near fire:

012809 054.JPG

Ouch, and I’m sure that smells very nice too.

Yes very close but that was where the vent gets very hot not so with the roof penetration. I am still not giving it up yet tomorrow is another day and I have not even down loaded my pic from today’s inspection shame shame see ya.;-):smiley: