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  1. #1
    RobertSmith's Avatar
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    Default Dryer exhaust vent

    Last edited by RobertSmith; 12-20-2007 at 12:49 PM.
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  2. #2
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    Default Re: Dryer exhaust vent

    That looks like the foil type, not plastic. I have seen foil that is UL listed for dryers. Not ideal, for sure.

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
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  3. #3
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    Cool Re: Dryer exhaust vent

    OK for its location (exposed) but once it enters the wall until it exits the home, smooth non-combustible duct material only. 2006 UMC 905.4

    Jerry McCarthy
    Building Code/ Construction Consultant

  4. #4
    David Banks's Avatar
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    Default Re: Dryer exhaust vent

    Check your local codes. Plastic not allowed in MA. Foil is.
    I put something like this in my report.
    DRYER VENTING:
    : Suggest rigid metal vent pipe (Aluminum or galvanized) for dryer. Vents should not be connected with sheet metal screws.
    :Foil aluminum or plastic type not recommended as these can catch lint. Potential fire hazard issue.
    : Flexible transition ducts shall not be concealed within construction.


  5. #5
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    Default Re: Dryer exhaust vent

    Quote Originally Posted by John Arnold View Post
    That looks like the foil type, not plastic. I have seen foil that is UL listed for dryers. Not ideal, for sure.
    Quote Originally Posted by Jerry McCarthy View Post
    OK for its location (exposed) but once it enters the wall until it exits the home, smooth non-combustible duct material only. 2006 UMC 905.4
    Neither the white plastic nor those aluminized mylar "foil" (which are still plastic) are approved for use with dryers.

    The foil ones have a UL listing, for air ducts, not for dryers, and, no manufacturer of dryers show their use is allowed in their manufacturer's installation instructions - at least none that I've read to date.

    They all want rigid metal dryer ducts and rigid metal dryer connectors (those short pieces are dryer connectors), and, if rigid metal dryer connectors are not possible, then flexible metal (made entirely of aluminum and are not "foil") dryer connectors are allowed.

    Thus, those foil ones need to re written up for replacement with either a rigid metal (preferred) or flexible metal (second choice) dryer connector.

    Jerry Peck, Construction / Litigation Consultant
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  6. #6
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    Default Re: Dryer exhaust vent

    Quote Originally Posted by Jerry Peck View Post
    The foil ones have a UL listing, for air ducts, not for dryers,
    I'll look again when I'm in the Big Orange Box, but I could have sworn I saw foil ones UL listed for dryers.

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
    www.ArnoldHomeInspections.com

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    Default Re: Dryer exhaust vent

    Quote Originally Posted by John Arnold View Post
    I'll look again when I'm in the Big Orange Box, but I could have sworn I saw foil ones UL listed for dryers.

    Even if you find one that is, the dryer manufacturer states DO NOT USE them, and, thus, they are not allowed to be used.

    Read the dryer instructions and look in the WARING! and RISK OF FIRE! sections.

    Jerry Peck, Construction / Litigation Consultant
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  8. #8
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    Cool Re: Dryer exhaust vent

    Many mfrs such as Maytag used to state in their manuals if combustible venting used ,it voided the warranty of the appliance.

    While the code allows limited use of corrugated metal hose, it does no good if the duct is crushed or mishapened to where it blocks flow. In the photo, you see a flex duct that was not trimmed to length. This can easily block reducing airflow which can overheat the unit, cause a fire, premature component failure and lint blowback into the guts of the machine. Don't rely on snap switches alone for safety-they are designed, mfd. and installed by man, thus prone to failure.

    Keep the fire in the fireplace.

  9. #9
    imported_John Smith's Avatar
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    Default Re: Dryer exhaust vent

    Our local radio host (Tom Tynan) that seems to have a chip on his shoulder for home inspectors told a caller this morning that it was acceptable to use the flexible ducting through out the attic. Surely this guys not wrong. He's on the radio.


  10. #10
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    Cool Re: Dryer exhaust vent

    Should have taken the time to post the appropriate codes rather than shoot from the lip.

    2006 Uniform Mechanical Code
    905.4 Exhaust Ducts for Type 1 Clothes Dryers.
    (A) A clothes dryer exhaust duct shall not be connected into any vent connector, gas vent, chimney, crawl space, attic, or other similar concealed space.
    (B) Ducts for exhausting clothes dryers shall not be assembled with screws or other fastening means that extend into the duct and that would catch lint and reduce the efficiency of the exhaust system.
    (C) Exhaust ducts shall be constructed of rigid metallic material. Transition ducts used to connect the dryer to the exhaust duct shall be listed for that application or installed in accordance with the clothes dryer manufacturer's installation instructions. [NFPA 54:9.4.4]

    2006 IRC:
    SECTION M1502
    CLOTHES DRYER EXHAUST

    M1502.1 General. Dryer exhaust systems shall be independent of all other systems, and shall convey the moisture to the outdoors.
    Exception: This section shall not apply to listed and labeled condensing (ductless) clothes dryers.
    M1502.2 Duct termination. Exhaust ducts shall terminate on the outside of the building. Exhaust duct terminations shall be in accordance with the dryer manufacturer’s installation instructions. Exhaust ducts shall terminate not less than 3 feet (914 mm) in any direction from openings into buildings. .Exhaust duct terminations shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination
    M1502.3 Duct size. The diameter of the exhaust duct shall be as required by the clothes dryer’s listing and the manufacturer’s installation instructions.
    M1502.4 Transition ducts. Transition ducts shall not be concealed within construction. Flexible transition ducts used to connect the dryer to the exhaust duct system shall be limited to single lengths, not to exceed 8 feet (2438 mm) and shall be listed and labeled in accordance with UL 2158A.
    M1502.5 Duct construction. Exhaust ducts shall be constructed of minimum 0.016-inch-thick (0.4 mm) rigid metal ducts, having smooth interior surfaces with joints running in the direction of air flow. Exhaust ducts shall not be connected with sheet-metal screws or fastening means which extend into the duct.
    M1502.6 Duct length. The maximum length of a clothes dryer exhaust duct shall not exceed 25 feet (7620 mm) from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.8 rad) bend and 5 feet (1524 mm) for each 90-degree (1.6 rad) bend. The maximum length of the exhaust duct does not include the transition duct.
    Exceptions:
    1. Where the make and model of the clothes dryer to be installed is known and the manufacturer’s installation instructions for the dryer are provided to the building official, the maximum length of the exhaust duct,

    Photo of acceptable transition of clothes dryer duct to rigid metal duct passing into wall framing.

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    Jerry McCarthy
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    Default Re: Dryer exhaust vent

    Quote Originally Posted by Jerry McCarthy View Post
    Photo of acceptable transition of clothes dryer duct to rigid metal duct passing into wall framing.
    Correct.

    That is the correct stuff if you are using flexible dryer connector instead of rigid metal dryer connector (referred to in those code references as 'transition duct'.)

    That foil stuff ... that's a no-no.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  12. #12
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    Default Re: Dryer exhaust vent

    This seems like one of those 'no enforcement possible' codes.... how many times is there a dryer installed when the house is given its final occupancy?

    It probably explains why the majority of the ones we see in use are wrong according to the code. I'm sure 9 of 10 people that walk into HD and ask the kid for a dryer vent are given the wrong one.


  13. #13
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    Default Re: Dryer exhaust vent

    Quote Originally Posted by Matt Fellman View Post
    This seems like one of those 'no enforcement possible' codes.... how many times is there a dryer installed when the house is given its final occupancy?

    It probably explains why the majority of the ones we see in use are wrong according to the code. I'm sure 9 of 10 people that walk into HD and ask the kid for a dryer vent are given the wrong one.
    That is why I keep posting this article and have the link embedded in all of my reports

    Dryer Venting Guidelines - How to avoid dryer fire hazards

    None of use real knows what takes place upon possession transfer, in most cases.

    badair http://www.adairinspection.com Garland, TX 75042 TREC # 4563
    Commercial-Residential-Construction-EIFS-Infrared Thermography
    life is the random lottery of events followed by numerous narrow escapes

  14. #14
    Joseph Michalski's Avatar
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    Default Re: Dryer exhaust vent

    Good article, Barry - I think I will begin to add the link in my helpful hints as well.

    Also, thank you for the clear picture of the appropriate type of flex vent (whoever posted it). Often a picture speaks far more clearly to the client than I can.


  15. #15
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    Default Re: Dryer exhaust vent

    In the attic, the dryer exhaust duct went from solid to flexible metal, then back to solid....the flexible metal is improper, correct? They should had used solid?

    Also,

    1) Should there be a rise in duct run? It was routed directly on the ceiling joists , then out to the exterior.

    2) What's is everyone's take on the vertical run upwards through the wall cavity? Isn't vertical runs bad? Should be blower assited?


  16. #16
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    Default Re: Dryer exhaust vent

    Flex ducting is incorrect except for the short distance from the back of the dryer to the rigid metal. There's no required slope that I'm aware of. IMO.... vertical venting of a dryer is a poor idea but it's allowed. The booster fan requirements are based on overall length. Also, there are reductions for bends in the line.

    There are some fairly specific but simple requirements (codes)... Google a couple key terms and you should find them. Somebody here might post something too.


  17. #17
    chris mcintyre's Avatar
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    Default Re: Dryer exhaust vent

    Total length allowed is 25' with a 2 1/2' reduction for 45's and 5' reduction for 90's.


  18. #18
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    Default Re: Dryer exhaust vent

    <LI class=bullet>Flexible transition hose between the dryer and the wall outlet should be either the foil type or the aluminum flexible duct (most preferred). Do not use the plastic or vinyl.

    I lifted this from the dryer vent guidelines link.


  19. #19
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    Default Re: Dryer exhaust vent

    I believe this same link also states the max length is 35 feet.


  20. #20
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    Default Re: Dryer exhaust vent

    Quote Originally Posted by Don Schlecht View Post
    <LI class=bullet>Flexible transition hose between the dryer and the wall outlet should be either the foil type or the aluminum flexible duct (most preferred). Do not use the plastic or vinyl.

    I lifted this from the dryer vent guidelines link.
    The "foil type" is not allowed. Neither is the plastic or the vinyl type.

    Flexible metal dryer connector duct is allowed - connector duct is the up-to-8-foot-long-piece-which-is-outside-the-wall-and-connects-between-the-dryer-and-the-dryer-duct-in-the-wall.

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

  21. #21
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    Default Re: Dryer exhaust vent

    I agree it is not allowed. I also question the 35' duct length.

    I was just pointing out a couple of problems I found in the link.

    The owner of the website should be advised of this incorrect information.


  22. #22
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    Default Re: Dryer exhaust vent

    Quote Originally Posted by Don Schlecht View Post
    I believe this same link also states the max length is 35 feet.
    The maximum length is "effective length" and is 25 feet for "unknown" dryers. When the dryer manufacturer and model is "known" the length can be up to that shown in the installation instructions for that particular model dryer - some go up to 90 feet.

    Which is really great when you think about those people moving, taking that dryer with them, and a new owner coming in and installing a standard dryer which may only be rated to pus 30 feet or so ... and pushing the air into a 90 foot long effective length duct ... which is not going to work.

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

  23. #23
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    Default Re: Dryer exhaust vent

    Quote Originally Posted by Don Schlecht View Post
    I agree it is not allowed. I also question the 35' duct length.

    I was just pointing out a couple of problems I found in the link.

    The owner of the website should be advised of this incorrect information.
    Called today and it's been updated
    They based their previous info on the 2009 IMC
    504.6.4.1 Specified length. The maximum length of the
    exhaust duct shall be 35 feet (10 668 mm) from the connection
    to the transition duct from the dryer to the outlet
    terminal. Where fittings are used, the maximum length
    of the exhaust duct shall be reduced in accordance with
    Table 504.6.4.1

    badair http://www.adairinspection.com Garland, TX 75042 TREC # 4563
    Commercial-Residential-Construction-EIFS-Infrared Thermography
    life is the random lottery of events followed by numerous narrow escapes

  24. #24
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    Default Re: Dryer exhaust vent

    Thank You


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