# Roof flashing for gas appliance vents



## klarenbeek (Sep 17, 2013)

Has anyone seen these flashings used on metal roofs for gas appliance vents like b vent? They do not meet the code defenition for non-combustible, so I made the call they can't be used for b vent flashing.  I have a major box store building a new location here and they say this is the first time they have ever had a problem using these.

View attachment 1945


doc20130907132642.pdf

doc20130907132642.pdf


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## Gregg Harris (Sep 17, 2013)

klarenbeek said:
			
		

> Has anyone seen these flashings used on metal roofs for gas appliance vents like b vent? They do not meet the code defenition for non-combustible, so I made the call they can't be used for b vent flashing.  I have a major box store building a new location here and they say this is the first time they have ever had a problem using these.


I would not have a problem using them in your application with B vent. The EPDM as shown can withstand 240 degrees constant or 302 intermittent. The Red silicone model 392 constant or 482 intermittent.

Category 1 appliances have a maximum design flue temperature of 550 degrees at the outlet of the appliance and generally run around 350 degrees at the outlet. This will give you a surface temperature on the outside of the B vent at the appliance of approximately 150 Degrees. Now take into consideration that the higher the vent the lower the temperature will get. If the flue pipe is designed properly it will reach the outside of the structure before it reaches it's dew point.

UL 441 requires a maximum of 90 degrees plus ambient for the outside of the B vent.


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## klarenbeek (Sep 19, 2013)

What code section would allow this?

 Section 502 of IFGC requires b vent to be installed per manufacturer's instructions, which for every brand of b vent is 1" clearance to combustibles.  Code definition of combustible is any material that does not meet the requirements of non-combustible.  The code definition of non-combustible is a material that meets certain criteria when tested in accordance with ASTM E 136 (I don't have my books in front of me right now for those criteria). These flashing do not meet that requirement.

In addition to using these flashings for b vent, they are also being used on the vent systems of several direct vent unit heaters where the vent system is a 4" single wall metal vent pipe with a 8" single wall pipe around it to bring in combustion air. The box installed inside the building behind the heater is a factory assembly from the manufacturer, but the pipe is all field assembled standard round sheet metal pipe.  Single wall vent pipe (which this is, it is not a listed assembly) requires 6" clearance to combustibles, this configuration only give 2" from the single wall to the flashing.

Again, this is a major national box store club chain that has builds stores across the country, and they claim this has never been an issue before.


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## Glennman CBO (Sep 19, 2013)

The intent of the clearances to combustibles is so that things won't catch fire. If the temperatures are good, then so am I.


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## zigmark (Sep 23, 2013)

klarenbeek-

Stand your ground and don't succumb to the pier pressure.  If they want to propose something other than code prescribed or listed allowances let them apply for alternate means with all required documentation to support their position.  Remember that all big business considers everything negotiable.  "No one else makes us do it that way", "we've never heard that requirement before", "we've been doing it this way for the past XXX years" are all typical manipulations used to put you on the defensive.  If you have taken the time to ensure you are interpreting and applying the requirement correctly stick with it.  Mr. Glennmans' previous post indicates that clearances to combustibles are so that things don't catch fire.  What he fails to mention in this application is that the product may fail from repeated heating and cooling long before catching fire and not provide the weather resistance it was installed for in the first place.  Now if they can document the conditions as he described them in his posts and the temperatures can be shown to be within the listed operating temperatures of the product they propose to use, assuming the manufacturers listing covers this, then allow it.  Making them provide the documentation and analysis is what you hang your hat on at that point.

Good Luck

ZIG


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## klarenbeek (Sep 29, 2013)

The local HVAC contractor told me the manufacturer let them know that although the flashings are rated for high temp, they do NOT meet the noncombustible criteria for ASTM E 136 that code requires. After several more emails and conversations with the retailer's team, they finally settled on the same solution that the HVAC installer on site and myself came to within 2 minutes of my seeing the flashings-- use metal roof flashings.


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## RJJ (Sep 29, 2013)

Klarenbeek I would agree!


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