Proper Size Gas Pipe to Dryer?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by statjunk, Apr 7, 2010.

  1. statjunk

    statjunk DIY Senior Member

    Messages:
    542
    Hello All,

    It's been a while since I've been on here. I hope that most everyone is still on here. Feels like it's been a year or so since I've been on here. In that time I've gotten married, had a son, folded my contracting business, got laid off from my day job, found another day job wheeeee. Just writing that makes me tired.

    The issue I'm dealing with here is I have a dryer sitution. I don't believe the dryer is getting enough gas to heat. It takes three hours to dry a load. Surprising it took me two dryers to actually check the gas line. Turns out someone ran 3/8" OD soft copper from the attic down to the dryer. So that means it's 1/4" ID.

    Total run length is 8-10 feet and junctions from a 3/4" to 1/2" black pipe "T".

    It's in a very tight spot in the attic and can't be gotten from below because of existing cabinetry. So I want to use soft pipe.

    Would 1/2" OD soft copper be sufficient to run a dryer?

    How about if coming off the T are two 1/2" S. 90's in order to line it up. Essentially I'm using the 90's to keep the soft copper below the joists. Otherwise it will have to be above an susceptible to damage.

    Thanks

    Tom
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Slow dry time is ALMOST always caused by a blocked exhaust duct. In your case, it might actually be the gas line. 1/4" ID is pretty small . 30 feet of that supports only about 10,000 BTU and I suspect a dryer is a lot more than that. For 1/2" ID, 30 feet supports about 47,000 BTU/

    [​IMG]
    Last edited by a moderator: Apr 29, 2011
  3. statjunk

    statjunk DIY Senior Member

    Messages:
    542
    Hey Jimbo,

    Any idea what 3/8" ID supports? It's a 10' run.

    Thanks

    Tom
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,270
    Location:
    Cave Creek, Arizona
    Gas lines often "support" more btus than the charts list, because the burners will still operate at less pressure than the charts assume, but 3/8" copper might be too small. Have you looked at the burner flame while the dryer is operating?
  5. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    3/8 ID at 10 feet is listed at 420000 BTU. That is why it is usually OK to use a 3/8 ID 3 foot long flex gas connector for dryers.

    I get these figures from the National Fuel Gas Code charts, also found in the CA Plumbing Code book. I use the chart for copper, less than 2.0 PSIG, 0.3" wc drop. There is a slightly less conservative chart for 0.5" wc drop.
  6. statjunk

    statjunk DIY Senior Member

    Messages:
    542
    Thanks guys. I really appreciate the info. The dryer states on it that it's 22,500 BTU. So a 10' run of 1/2" OD - 3/8" ID should do the trick. Anyone care to guess what I'll be doing this weekend?

    Tom
  7. gator37

    gator37 Retired prof. engr.

    Messages:
    108
    Location:
    Alabama
    Jimbo is correct. One source is NFPA 54 for pipe sizing charts.
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