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  1. #1
    Bill Taylor's Avatar
    Bill Taylor Guest

    Exclamation Dryer vent in crawl space

    My dryer vent is into crawl space right now, but I am going to run it about 15 feet with two elbows and out through the foundation wall into a carport. what could I do to make sure it works well, and to contain lint in carport? Other option would be to go straight across the crawl space about 30 feet and out through the foundation wall there. Is distance a problem, as compared to the two ells going back to carport option. I may someday enclose carport with garage door as well.
    I created this mess by adding a room and moving the laundry, so I'm the source of the problem.

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  2. #2
    James Duffin's Avatar
    James Duffin Guest

    Default Re: Dryer vent in crawl space

    Here is what the NC Code says...



    SECTION 504
    CLOTHES DRYER EXHAUST

    504.1 Installation.
    Clothes dryers shall be exhausted in accordance
    with the manufacturer's instructions. Dryer exhaust systems
    shall be independent of all other systems and shall convey
    the moisture and any products of combustion to the outside of
    the building.
    Exception:


    This section shall not apply to listed and labeled
    condensing (ductless) clothes dryers.
    504.2 Exhaust penetrations.


    Ducts that exhaust clothes dryers
    shall not penetrate or be located within any fireblocking,
    draftstopping or any wall, floor/ceiling or other assembly
    required by the

    International Building Code to be fire-resistance
    rated, unless such duct is constructed of galvanized steel or aluminum
    of the thickness specified in Section 603.4 and the
    fire-resistance rating is maintained in accordance with the

    International
    Building Code.

    Fire dampers, combination fire/smoke
    dampers and any similar devices that will obstruct the exhaust
    flow, shall be prohibited in clothes dryer exhaust ducts.
    504.3 Cleanout.


    Each vertical riser shall be provided with a
    means for cleanout.
    504.4 Exhaust installation.


    Dryer exhaust ducts for clothes
    dryers shall terminate on the outside of the building and shall
    be equipped with a backdraft damper. Screens shall not be
    installed at the duct termination. Ducts shall not be connected
    or installed with sheet metal screws or other fasteners that will

    obstruct the exhaust flow. Clothes dryer exhaust ducts shall not
    be connected to a vent connector, vent or chimney. Clothes
    dryer exhaust ducts shall not extend into or through ducts or
    plenums.
    504.5 Makeup air.


    Installations exhausting more than 200 cfm
    (0.09 m

    3/s) shall be provided with makeup air. Where a closet is
    designed for the installation of a clothes dryer, an opening having
    an area of not less than 100 square inches (0.0645 m

    2) shall
    be provided in the closet enclosure.
    504.6 Domestic clothes dryer ducts.


    Exhaust ducts for
    domestic clothes dryers shall be constructed of metal and shall
    have a smooth interior finish. With the exception of the transition
    duct flexible ducts are prohibited The exhaust duct shall
    be a minimum nominal size of 4 inches (102 mm) in diameter.
    The entire exhaust system shall be supported and secured in
    place and shall terminate not less than 12 inches (305 mm)
    above finished grade. The male end of the duct at overlapped
    ductjoints shall extend in the direction of airflow. Clothes dryer
    transition ducts used to connect the appliance to the exhaust
    duct system shall be limited to single lengths not to exceed 8
    feet (2438 mm) and shall be listed and labeled for the application.
    Transition ducts shall not be concealed within construction
    and must remain entirely within the room in which the
    appliance is installed.
    Exception:


    Where the duct termination is less than 12
    inches (305 mm) above finished grade an areaway shall be
    provided with a cross-sectional area not less than 200 square
    feet (186m..) The bottom of the duct termination shall be
    no less than 12 inches (305 mm) above the areaway bottom
    504.6.1 Maximum length.


    The maximum length of a
    clothes dryer exhaust duct shall not exceed 45 feet (13 716
    mm) from the dryer location to the outlet terminal. The maximum
    length of the duct shall be reduced 5 feet (1524 mm)
    for each 45 degree (0.79 rad) bend and 10 feet (3048 mm)
    for each 90 degree (1.6 rad) bend. The maximum length of
    the exhaust duct does not include the transition duct.

    &e..
    Table 603 4 for gage thickness
    Exception:


    Where the make and model of the clothes
    dryer to be installed is known and the manufacturer's
    installation instructions for such dryer are provided to the
    code official, the maximum length of the exhaust duct,
    including any transition duct, shall be permitted to be in
    accordance with the dryer manufacturer's installation
    instructions. Where exhaust ducts are installed in concealed
    locations the developed length of the exhaust
    duct system shall be indicated by permanent labels or
    tags installed in an observable location.
    504.6.2 Rough-in required.


    Where a compartment or
    space for a domestic clothes dryer is provided, an exhaust
    duct system shall be installed in accordance with Sections
    504.6 and 504.6.1.
    504.7 Commercial clothes dryers.


    The installation of dryer
    exhaust ducts serving Type 2 clothes dryers shall comply with
    the appliance manufacturer's installation instructions. Exhaust
    fan motors installed in exhaust systems shall be located outside
    of the airstream. In multiple installations, the fan shall operate
    continuously or be interlocked to operate when any individual

    unit is operating. Ducts shall have a minimum clearance of 6
    inches (152 mm) to combustible materials. Clothes dryer transition
    ducts used to connect the appliance to the exhaust duct
    system shall be limited to single lengths not to exceed 8 feet
    (2438 mm) in length and shall be listed and labeled for the

    application. Transition ducts shall not be concealed within con struction




  3. #3
    Join Date
    Mar 2007
    Location
    Ormond Beach, Florida
    Posts
    26,252

    Default Re: Dryer vent in crawl space

    Most clothes dryers are rated to push at least 50 feet (although there are some which will only push 35 feet or so), and some are rated to push up to 90 feet, so you really need to get the manufacturer and model number of your dryer and the installation instructions and find out what your dryer is rated for.

    The two 90 ells equals 10 feet, unless you can use long radius ells, in which case the long radius ells are factored in at 18 inches each, or 3 feet for two long radius ells ... 3 feet versus 20 feet makes a big difference in the effective length of the dryer duct.

    Another item which affect allowed dryer duct length is the exhaust hood - this is addressed in the installation instructions instead of in the code: typically the louver type and the hood type are rated the same and have less restriction, thus more duct length is allowed, than the angled/sloped exhaust hood.

    The short answer, then, is to read your installation instructions.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  4. #4
    Join Date
    Feb 2009
    Location
    Southern Vancouver Island
    Posts
    4,549

    Default Re: Dryer vent in crawl space

    A long straight run should be alright. Elbows tend to trap moisture. The carpot is not an ideal destination. Use metal foil tape, not screws, to secure the pipes together.

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    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  5. #5
    Join Date
    Mar 2007
    Location
    Ormond Beach, Florida
    Posts
    26,252

    Default Re: Dryer vent in crawl space

    Quote Originally Posted by John Kogel View Post
    A long straight run should be alright.
    But "how long"? Even long straight runs can be too long.

    Elbows tend to trap moisture.
    Typically, it is hard to have less than two elbows (unless one of the newer dryer boxes is recessed into the wall as they all a straight up (or down) connection instead of a 90 elbow, then you still have one at the top or the bottom where it turn across the attic or crawlspace.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

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