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Thread: water heater venting

  1. #1

    Default water heater venting

    Is there any online charts that anyone knows of for sizing flues ( not the chimney) based on btu's? I know it's in the code book, but I don't have access to one recently my copy got "vanished". It's just something my boss said he was going to start asking in our meetings, asking people questions related to gas sizing and water heater flue sizing questions. I'm not a full journeyman.....yet.
    In one state you have to upgrade the flue to 4", in another you can still use 3" on like a 50 gallon gas. Does anybody know why there's this difference?

  2. #2
    Licensed Grump GrumpyPlumber's Avatar
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    It depends on whether your states uses the NFPA, IF so...you can download it online for about $35 from Techstreet.
    I can tell you the formula for a common vent on gas fixtures, but there's a chart in the book for size vs BTU...maybe later I'll look it up.
    Whatever ya do...NEVER change the MFG size.
    "The biggest regrets we have in life are the chances we never took."

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    Master Plumber master plumber mark's Avatar
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    Talking its just stupid politics at its very best....

    In one state you have to upgrade the flue to 4", in another you can still use 3" on like a 50 gallon gas. Does anybody know why there's this difference?[/quote]

    IAround here we can use 3 inch on a water heater except
    for any type of city jobs around here. They force us to increase the size to
    4 inch....on a standard heater....which means running
    a new chimmney however far to make the inspectors happy


    the stupid thing about it is the open hood vent on most
    all water heaters reduce the size of the chimmney to 3 inch
    right from the start at the flu hood.......

    so basically.. you have restricted the vent right to 3
    inch from the start


    you could not run 4 inch from something and
    reduce it down to three going into a chimmney,
    they would jump up and down about that.

    I hope that some inspector never realizes this
    and tries to make everyone get larger hood vents for the
    heaters to " pass code.." ..

    they will argue that fumes could escape
    out the bottom of the hood vent which is about 6 inch
    before getting into the 4 inch pipe.


    I dont think that they make them..or ever have.

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    Plumber jimbo's Avatar
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    In most cases, the controlling authority is the National Fuel Gas Code. That book is inexpensive, and available on line. It is a "must have".

    Also, it is a code requirement that a water heater be installed in accordance with it's manufacturer's instructions. Generally, these call out the Fuel Gas Code as their reference, so there you go!

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    Licensed Grump GrumpyPlumber's Avatar
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    OK...it's in Ch. 13 of the nat'l fuel & gas code, I'm gonna let you look it up.
    Also, law requires any manufacturer to include a copy of the code with the fixture.
    So, you could simply look at the manual on the heater for your answer.
    Perry...the sooner you aclimate yourself to the code book, familiarize yourself with rough memorization on what chapters have what info, the better off you'll be.
    Once you get your license, looking up code isn't going to be to win arguments anymore...it'll be your livelyhood.
    Last edited by GrumpyPlumber; 08-10-2007 at 06:31 AM.
    "The biggest regrets we have in life are the chances we never took."

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    Moderator & Master Plumber hj's Avatar
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    Default manual

    "Look in the manual on the water heater"? Now isn't that a unique idea? I will have to try that sometime, not.

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    Licensed Grump GrumpyPlumber's Avatar
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    Quote Originally Posted by hj
    "Look in the manual on the water heater"? Now isn't that a unique idea? I will have to try that sometime, not.

    It's all over the code book..."Refer to manufacturer instruction".
    The manufacturer has to be code approved obviously, but...you're kidding...right?
    Any inspection I've done on a boiler/water heater..etc, the inspector wants the manual there so he can see what the specs call for.
    You didn't know this?
    In my state (and likely most) the MFG is legally obligated to include an actual copy of relative code as well.
    "The biggest regrets we have in life are the chances we never took."

  8. #8

    Default Thanks much

    thank you all for the replies to that. I hate to say it but I've never really looked at the manual on most heaters except maybe powervents to see if what was there was going to work.

    The upgrades, I was doing a little google type research, and what I've come up with is I think what they're worried about now is that there's something called "orphaning" of a chimney. The original chimney in a house with say a gas furnace or oil fired furnace....even old ones that had a coal furnace....the chimney was apparently sized for both, a furnace, and a water heater.... and now with more and more people going to these high output super high efficiency furnaces that are basically like a power vent water heater, and discharge out the side of the house, now the water heater is all alone with that great big space, and the cold air in winter apparently is more than just the water heater can overcome and the exaust gets pushed back down and backs up out the hood....I don't know if that really is why, but that's maybe why.

    But I'm going to really learn all the gas stuff. I'm gonna look for that fuel gas book, thanks. You know, as much as a pain in the butt as it is to get licensed, keep up with all that etc...there's one thing, the more technical they get the less home owners and jack leg plumbers will be doing the work, the more business for plumbers.

  9. #9
    Master Plumber Dunbar Plumbing's Avatar
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    Quote Originally Posted by perrycat
    Is there any online charts that anyone knows of for sizing flues ( not the chimney) based on btu's? I know it's in the code book, but I don't have access to one recently my copy got "vanished". It's just something my boss said he was going to start asking in our meetings, asking people questions related to gas sizing and water heater flue sizing questions. I'm not a full journeyman.....yet.
    In one state you have to upgrade the flue to 4", in another you can still use 3" on like a 50 gallon gas. Does anybody know why there's this difference?

    The heaters in my area when they are 60 gallons or more, the flue diverter will automatically be a 4" flue diverter with no ability to size down.

    In all applications....the flue chase of any water heater has to be matched, never decreased as it leaves the unit and heads to the B vent or chimney.

    Those heaters with a 4" flue diverter only will have a 4" flue chase to the burner assembly, not 3".

    I believe that anything above 55,000 BTU's requires a 4" flue...not sure on that but I know I'm close.

    http://www.uscarb.com/natural-gas-chart.htm
    Last edited by Dunbar Plumbing; 08-10-2007 at 08:21 PM.
    Read what the end of this sentence means.

  10. #10
    Licensed Grump GrumpyPlumber's Avatar
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    Sounds 'bout right RUGGED, though linear distance has some effect on sizing...I'm usually reading up on boiler venting as opposed to heaters as switch outs are generally a straight shot..
    Just to stress the importance of reading the manual...I once watched a fella take two days to dismantle a powervented 75 gal heater because it would fire up, then stop.
    He tried "everything" he could think of and finally drained it down & dismantled it, called in an order for all new replacement parts.
    I'd been on a house next door in the same complex (new) wrapping up the gas piping and testing, I finally went over to check in on him and..well...it wasn't good...there were parts everywhere.
    I'd stopped in the first day and he snapped at me, I was new with the co, so I just went back to my own work...as instructed by the owner the day before. ("He isn't licensed, but this is his job, let him work alone")
    I picked up the manual which he'd tossed to the side after looking up and seeing he had 2" PVC running to the sill from the heater...I knew what the trouble was, but he'd been very defensive so I'd kept my distance to this point.
    I opened the manual to the "venting" section, where in BOLD lettering it stated "WARNING: DO NOT USE LESS THAN 3" DIAMETER VENTING".
    He'd installed a few 40 & 50 gal power vents, but this was apparently his first 75.
    Cost the company 2 days labor, I left not long after.
    Thank GOD heaters and gas appliances come with so many safeties now.
    "The biggest regrets we have in life are the chances we never took."

  11. #11
    DIY Senior Member construct30's Avatar
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    the stupid thing about it is the open hood vent on most
    all water heaters reduce the size of the chimmney to 3 inch
    right from the start at the flu hood.......

    so basically.. you have restricted the vent right to 3
    inch from the start


    you could not run 4 inch from something and
    reduce it down to three going into a chimmney,
    they would jump up and down about that.

    I hope that some inspector never realizes this
    and tries to make everyone get larger hood vents for the
    heaters to " pass code.." ..

    they will argue that fumes could escape
    out the bottom of the hood vent which is about 6 inch
    before getting into the 4 inch pipe.


    I dont think that they make them..or ever have.[/QUOTE]


    Up sizing the pipe makes up for some elbows and longer runs to a certain degree. You see it a lot on furnaces and hotwater tanks. It makes better draft on that 3" take off, less drag on the way to the chimney. However inspectors can come up with weird stuff from time to time. If it doesn't matter I don't argue, but if it's flat out wrong...

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