Building Code

Same As Straight Pipe

Building Codes & Information

Code Sections Specific To Dryer Venting:
Is The Dryerbox UL listed? Does it have any formal building or code approvals?
All five of our new construction DryerBox models have gone through official testing and have received UL Classification and subsequent one hour F & T Rating. All five of our models can be installed in a one hour wall assembly constructed of wood or metal framing provided certain additional installations of drywall and or insulation are accomplished. A summary of these requirements may be found at this link and the full UL listing details can be viewed at this link.
Do you have any information on "Clothes Dryer Building Code"?
Building codes vary from region to region (with amendments) and not all the jurisdictions follow the ICC or adopt ICC codes at the same time. In most cases they all basically include the same restrictions. Some codes have been found to be less restrictive. Many of them concur that the exception to the 35-foot minimum run length is when the appliance manufacturer's installation instructions specify maximum lengths with particular models. In this case, the make, model and installation instructions need to be provided to the building inspector and sometimes a permanently mounted sign or placard is placed behind the dryer identifying the overall length of the exhaust duct and the respective model that the house was approved with. A summary of the typical codes relating the dryer venting is as follows:
  • Dryer vent systems shall be independent of all other systems and shall convey the moisture to the outdoors.
  • Terminations shall be a minimum of three feet from property line and 12" above the ground and not exhibit any type of screen.
  • Vents and duct connections shall be connected mechanically (with sheet-metal screws or rivets) and shall not protrude more than 1/8" into vent.
  • Exhaust vents shall be equipped with a back-draft damper and no screen.
  • Vents shall be constructed of minimum 0.016-inch-thick (0.406 mm) rigid metal ducts, having smooth interior surfaces with joints running in the direction of air flow and having a minimum interior diameter of 4".
  • Flexible duct shall not be concealed within the construction.
  • The maximum length of a 4-inch (102 mm) diameter exhaust vent shall not exceed 35 feet (7620 mm) from the dryer location to wall or roof termination, and shall terminate with a full opening exhaust hood. A reduction in maximum length of 2.5 feet for each 45-degree bend and 5 feet for each 90-degree bend shall apply. Installations where this length is exceeded shall be installed in accordance with the manufacturer's installation instructions.
  • New for 2018 codes (adoption ~ midyear 2018) will require that the passageway through the termination hood not diminish in size and must maintain a minimum of 12.5 sq. inches of area. Also, the 4" round ductwork in the walls cannot be deformed, it must retain its round profile.
  • Click here to view the actual 2021 IMC - International Mechanical Code (section 504) and the 2021 IRC - International Residential Code (section 1502).
  • Click here to view the "Dryer Venting Guidelines".
I read a mechanical code that indicated a "cleanout" was required in the clothes dryer exhaust. What does that mean?
According to the 2003 International Mechanical Code for Dryer Exhaust Systems, Section 504.3 states that each vertical riser shall be provided with a means for cleanout - an accessible opening to remove all lint accumulation that settles in the lowest point of a vertical duct run. The opinion of professional engineers is that the well-designed Dryerbox meets the requirements as a cleanout opening and provides an excellent means of transitioning from the dryer’s flexible connection to the dryer’s exhaust system through the wall. The clamped connections meet the requirements as a cleanout opening for the dryer vent system. Click here to download/print our "Sealed Engineers Letter" regarding the cleanout issue.
Correct, the new "International Mechanical Code" specifically states on "Section 504.3 Cleanout - Every vertical riser shall be provided with a means of cleanout." The intent of this code element is to provide an accessible means to remove the lint accumulation that would fall vertically (settle) to a low spot in the vertical run. If a means already exist to access this, (i.e., the usual ell through the drywall or a Dryerbox) then a cleanout is not required. Our engineers' professional opinion is that The Dryerbox meets the requirements as a cleanout opening for the dryer exhaust system. Click here to download/print our "Sealed Engineers Letter" regarding the cleanout issue.
What are my options if the distance to the outside is greater than code allows?
You do have options. Currently most if not all mechanical codes allow for longer exhaust duct runs than 25 feet if the manufacturer of the dryer appliance specifies or allows for lengths exceeding the local governing mechanical code. In most cases you'll have to provide the specs and related literature at time of mechanical rough and final inspections and may be required to have the respective appliance installed at final, but please concur this with your building inspector. Findings: Selecting a mid-range priced dryer from each of the four big dryer manufacturers, and reviewing each of their respective installation guides, maximum exhaust distances with two elbows ranged from 26 feet to 44 feet, but were achieved by using hard rigid snaplock pipe in the walls, and a "box hood" or "louver style" weather hood. Click here to view the comparison of four dryer manufacturers' installation specs. The other options are using the Fantech - Dryer Boosting In-Line Fan or the same as straight pipe Dryer-Ell, and you can check our line of dryer accessories available at our Fast and Secure Online Ordering by clicking here.
Our inspector wants to know what affect a slightly "ovalized" exhaust might have on CFM (Cubic Feet per Minute).
To start, the dryer's CFM data can be obtained from the OEM's operational manual and is mostly a function of the size of the motor. That information would be relevant to standard 4" round Snaplock pipe at 12.43 square inches for the interior of perfectly round pipe. Compare that to the very slightly oval openings for models 425, 4D and 3D with 12.14" which would be 2% less than perfectly round. And the more oval model 350 (designed to fit in 2X4 walls where the pipe has to be compressed to fit in the wall) has 11.65" which is 6% less. The resulting impact on CFM would, therefore, be nominal.