Good dryer venting information here:http://www.appliance411.com/faq/dryer-vent-length.shtml
Good stuff thanks
I agree Waybe and thank you John, always good information to convey.
I also would like to reccomend this reccessed dryer box that eliminates the crushing of the flex dryer hoses.
Marcel 
I always recommend the flex vents be replaced.
The U.S. Consumer Product Safety Commission estimates that in 1998, clothes dryers were associated with 15,600 fires, which resulted in 20 deaths and 370 injuries. Fires can occur when lint builds up in the dryer or in the exhaust duct. Lint can block the flow of air, cause excessive heat build-up, and result in a fire in some dryers.
To help prevent fires:
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Clean the lint screen/filter before or after drying each load of clothes. If clothing is still damp at the end of a typical drying cycle or drying requires longer times than normal, this may be a sign that the lint screen or the exhaust duct is blocked.
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Clean the dryer vent and exhaust duct periodically. Check the outside dryer vent while the dryer is operating to make sure exhaust air is escaping. If it is not, the vent or the exhaust duct may be blocked. To remove a blockage in the exhaust path, it may be necessary to disconnect the exhaust duct from the dryer. Remember to reconnect the ducting to the dryer and outside vent before using the dryer again.
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Clean behind the dryer, where lint can build up. Have a qualified service person clean the interior of the dryer chassis periodically to minimize the amount of lint accumulation. Keep the area around the dryer clean and free of clutter.
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Replace plastic or foil, accordion-type ducting material with rigid or corrugated semi-rigid metal duct. Most manufacturers specify the use of a rigid or corrugated semi-rigid metal duct, which provides maximum airflow. The flexible plastic or foil type duct can more easily trap lint and is more susceptible to kinks or crushing, which can greatly reduce the airflow.
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Take special care when drying clothes that have been soiled with volatile chemicals such as gasoline, cooking oils, cleaning agents, or finishing oils and stains. If possible, wash the clothing more than once to minimize the amount of volatile chemicals on the clothes and, preferably, hang the clothes to dry. If using a dryer, use the lowest heat setting and a drying cycle that has a cool-down period at the end of the cycle. To prevent clothes from igniting after drying, do not leave the dried clothes in the dryer or piled in a laundry basket.
I often see dryer ducts > 25 feet, often with bends. A few weeks ago, I inspected a house with a 30’ dryer vent, including two 90 degree bends. I say this:
“The dryer exhaust duct is considered to be too long. While we didn’t take precise measurements, we estimated it to exceed 25 feet, which is the maximum length that a straight duct should be according to today’s standards. Additionally, that 25 foot maximum length should be reduced by 2.5 feet for each 45 degree bend and 5 feet for each 90 degree bend. Service by a competent contractor is recommended to reduce the risk of fires due to a clogged vent.”
It has always been noted in the mechanical codes that dryer exhaust ducts shall not exceed the 25’ limit minus the 2.5’ for 45’s and 5’ for 90’s, but the bottom line is that the length is determined by the Manufacturer of the model of dryer in question.
Most brands of today exceed the maximum 25’ limit and for sh$ts and giggles, I looked up a Maytag Model MEDC400VW and found that for an inexpensive model the Manufacturer recommends smooth duct up to 44 feet with two 90 degree bends and 27’ with flex pipe.
So what we see in the field might not always be a safety concern.
During the inspection of the dryer installation, it was observed that the ridged exhaust vent duct for the dryer exceeds the rule of thumb limit of 25’.
It is recommended that a dryer installer specialist inspect the installation for proper adherence to the manufactures installation for the particular Model.
Improper installation of dryer vents have caused numerous fires due to excessive vent pipe lengths and type of pipe used.
Key Words= Manufacturers Instructions.
Hope this helps. :)
25 feet is not “rule of thumb?” It’s code.
My bad Joe:)
I call it a rule of thumb because it does not apply to all dryers.
Under M1501.3 the exception reads that where the make and model of the clothes dryer to be installed in known and the manufacturer’s installation instructions for such dryer are provided to the building official, the maximum legth of the exhaust duct, including any transition duct, shall be permitted to be in accordance with the dryer manufacturer’s installation instructions.
Now from the time the Code was written and todays dryer models have been improved, most dryers can exceed the 25’ limit with no problem.
So jotting down the Model # and researching the Manufactures instructions, might be prudent before we call it out as a safety defect.
JMHO:)
Any duct run that starts with 9’ (or more!) upward vertical run gets called out it if even approaches 25’.
IMHO the code does not pay enough attention to the fact that many builders start their installs with this vertical climb which will definitely impede the runs ability to convey lint and moisture.
Building Code is 25 feet from appliance with noted limitations
Manufacturer’s spec varies from code
Each installation requires a specific review to determine code compliance and need for repair and / or replacement.
That is correct Nanci.
The Code was written when?
The most important is to follow Manufactures Recommended intallations for whatever model is in question.
Therefore, one cannot just go out and say that a dryer does not meet code, because it exceeds the 25’ ruling of the Code. I now pronounce it as a rule of thumb.
Some dryers today can duct venting up to 45’ minus the bends, which far exceeds any codes of the 25’ ruling.
JMO:):D;)
Code compliance is based upon the applicable code which is in efect within the municipality where the home / building is in need of repair.
A recommended repair may (will most often) exceed building code. All building code compliant options available to client are discussed prior to proposal & installation.
The problem Marcel is builders have no prescient knowledge of the dryer to be installed and thus SHOULD comply with the limitations to the runs overall lengths that is/are dictated by code.
IMHO…:roll:
Correct
Absent of a (physical) Dryer installation, building code dictates the the requirement.
Where a particular manufacturer of a Dryer to be installed varies / deviates from minimum code, the appliance is noted as such and deemed compliant by AHJ.
A future replacement would require a determination based upon the manufacturer’s appliance recommendation (and applicable building code) along with AHJ interpretation of Building Code and manufacturer’s recommendations at the time of replacement / upgrade .
What complies today, may not comply in the future…
One might want to mention the 25 foot is code ( But seeing we are not code keepers ) Unless the manufacture states different. Recommend checking your dryer"s guild lines if information is not available contact the manufacture of your dryer.
I think we’re in an apples and oranges situation here.
Nanci you have the leisure of knowing the appliance installed and the requirements to best satisfy the needs of that appliance to comply with the Manufacturers’ installation instructions when recommending repair.
We as inspectors rarely see the dryer in the home as they normally do not convey; we are forced to recommend repairing to the lowest common denominator (Code is that minimum) and Marcel just points out that some Dryers will perform adequately and safely with runs which exceed the minimum…
I just don’t like 'em!!:mrgreen:
That is probably where my comprehension fails Mike. I cannot understand why it is so difficult to follow Manufactures Installation procedures and therefore we are left in the field of Inspections stating that the dryer venting is exceeding code limitations when it might not.
To report that a dryer vent does not meet the code requirement, is erroneous and should state that the venting might exceed the limitations of the Manufacturer and should be further evaluated by an appliance technician to assure that it does not become a safety hazard. :)
Correct
The 25 foot rule is the minimum standard.
Deviation from that is based upon the recommendations of the manufacturer of a particular appliance and acceptance by a local AHJ.
In those cases that we have encountered, the particular (specific) appliance is noted as compliant (and labeled as such).
A future replacement requires additional review for compliance at the time of installation.
Codes may vary and change.
Acceptance of an appliance installation may not be applicable to future replacement.
Marcel
y;-)u should be in the writing field or politics lol I like that!