Fuel gas code - distance between elbows

[bnymbill]

In AO Smith's power vent water heater instructions, it says to have 6" minimum between elbows for venting. It follows up by stating, "This is not intended to restrict venting options beyond those restrictions established by the current edition of the National Fuel Gas Code, ANSI Z223.1/NFPA 54."

Is anyone aware of a specific requirement in NFPA 54 about distance between elbows? I'll keep looking but figured someone may have stumbled onto this before.

 

[ICE]

This is not intended to restrict venting options beyond those restrictions established by the current edition of the National Fuel Gas Code,

The installation instructions for a listed product are to be followed as part of the listing. They say that it is not intended to restrict options .... so which is it? You do it or you don't?

 

[bnymbill]

The installation instructions for a listed product are to be followed as part of the listing. They say that it is not intended to restrict options .... so which is it? You do it or you don't?

My thoughts exactly, why create a gray area, just come out and say it's a requirement?! I can't find anything in NFPA 54 that directly covers this. So theoretically, I could use 2 90s back to back because AO Smith says it's not intending to restrict options...

 

[klarenbeek]

IFGC will simply direct you to manufacturer's instructions for PVC vented appliances and does not otherwise touch on sizing and design, so if the manufacturer has a 6" minimum between elbows that's what is required.

 

[ICE]

The NRTL that did the evaluation should be asked if they vetted the installation instructions. It has been my experience that sometimes they do and sometimes they don't. That is why I would never have a problem shooting down installation instructions.

 

[steveray]

My thoughts exactly, why create a gray area, just come out and say it's a requirement?! I can't find anything in NFPA 54 that directly covers this. So theoretically, I could use 2 90s back to back because AO Smith says it's not intending to restrict options...

Because manufacturers only care about selling products…

 

[Paul Sweet]

Elbows create restrictions to airflow. Having 90 degree elbows too close together creates even more turbulence and restrictions.

 

[Gregg Harris]

Note: The information provided in Figure 31 is intended as a guideline for good vent installation practices only and does not restrict venting options beyond those restrictions established by the current edition of the“National Fuel Gas Code, ANSI Z223.1/NFPA 54” or any applicable local and state codes.

So what it is telling you is the preferred method is to have a minimum of 6 inches between elbows and a maximum of 6 90's

 

[bnymbill]

Note: The information provided in Figure 31 is intended as a guideline for good vent installation practices only and does not restrict venting options beyond those restrictions established by the current edition of the“National Fuel Gas Code, ANSI Z223.1/NFPA 54” or any applicable local and state codes.

So what it is telling you is the preferred method is to have a minimum of 6 inches between elbows and a maximum of 6 90's

Thanks for following up on this, it's a weird line between preferred and required - wish they'd just make it black and white!

 

[Gregg Harris]

Thanks for following up on this, it's a weird line between preferred and required - wish they'd just make it black and white!

Unfortunately, manufactures do not want to be overly prescriptive in there installation manuals unless it is critical to the performance. This manufacturer could have suggested 45 degrees instead of 90 degrees.

A significant change in the HVAC industry was reducing the space from obstructions on the sides of the condensing units. This change does affect the performance of the equipment, but marketing factors heavily into the decisions to sell products with a smaller foot print.