Dryer Venting Forum

Please login or register.

Login with username, password and session length
Advanced search  

News:

SMF - Just Installed!

Author Topic: Calculating Equivalent Duct Length  (Read 12444 times)

Tim M

  • Guest
Calculating Equivalent Duct Length
« on: July 23, 2010, 10:06:14 AM »

.    Sorry to post this in this forum, but it it the ONLY one that allows me to post a new topic.

.    What are the values used to calculate Equivalent Duct Length?

Specifically in rigid pipe what does each of the following count as in additional feet?
Typical 90° elbow
Typical 45° elbow
Short 90° elbow

How does each of the same turns as above count as bends made in flex pipe?

How does straight flex pipe count vs rigid pipe?

How do each of the vent hoods count in feet?
4" opening (base of triangle viewed from side of hood)
2-1/2" opening
Louvered Hood
« Last Edit: August 16, 2013, 06:04:33 AM by rickharp »

rickharp

  • Administrator
  • Full Member
  • *****
  • Gender: Male
  • Posts: 147
    • View Profile
    • http://www.dryerbox.com
Re: Calculating Equivalent Duct Length
« Reply #1 on: July 26, 2010, 08:04:53 AM »

Quote from: Tim M
.    Sorry to post this in this forum, but it is the ONLY one that allows me to post a new topic.

.    What are the values used to calculate Equivalent Duct Length?
Equivalent Duct Length is the sum of the straight pipe that is concealed in the wall plus any 45 or 90 degree elbow deductions.  In most regions of the country, the ICC (International Code Council) governs the building code, and in that code each typical twisty turny elbow counts as 5 feet if it’s a 90 and 2.5 feet if its shape is a 45.  The UBC or Uniform Building Code allows for 15 feet of concealed dryer duct and they include two 90 degree ells.  There were some easing in the dryer venting codes recently with the ICC, namely the 2009 code, once adopted in your area, will allow for 35 feet total length. 
Specifically in rigid pipe what does each of the following count as in additional feet?
Typical 90° elbow - 5 feet
Typical 45° elbow - 2.5 feet
Short 90° elbow - If you are asking about the "Close Ell" by Builders Best, there is no specific or different reduction for that ell.  Likewise the Close Ell would carry the same 5 feet reduction, although it should be noted that it is likely that ell is more restrictive than the typical twisty turny ell. 

Note: the Long Turn Ells on the market now, do not carry a reduction in duct run and are counted as straight pipe.  In the instance of the Long Turn Ell, that is a net savings to the trade of 4.5 lineal feet. 

How does each of the same turns as above count as bends made in flex pipe?  - Flex pipe is prohibited in the walls (concealed) so this question is not relevant. 

How does straight flex pipe count vs rigid pipe? - Flex pipe is prohibited in the walls (concealed) so this question is not relevant. 

How do each of the vent hoods count in feet? - This is an area of concern for me and I am working on having the relative agencies create a Standard or Protocol that would regulate the minimums of back pressure these terminations or vent hoods create.  There are close to 25 different styles of vent hoods on the market.  Many of them exhibit back pressure levels in excess of the industry self-assumed rule of thumb (.16 w.c.i.). 
4" opening (base of triangle viewed from side of hood)
2-1/2" opening
Louvered Hood

Hope the above was helpful, feel free to add to this or reply.  Thanks
« Last Edit: August 15, 2013, 11:58:17 AM by rickharp »
Rick Harpenau
In-O-Vate Technologies, Inc
Jupiter, FL  33477
561-743-8696

Anonymous

  • Guest
Re: Calculating Equivalent Duct Length
« Reply #2 on: July 27, 2010, 07:16:40 AM »

Another option is to use the venting specifications set forth by the appliance manufacturers.  Depending on the capabilities of the unit's motor, these dryers can vent anywhere between 35 feet to 200 feet max.  The length reduction for elbows also varies. 

Some of these charts also show lengths when venting in flexible duct, which usually cuts the distance in half.  However, I agree with Rick that this duct cannot be concealed in the wall.
« Last Edit: August 15, 2013, 11:58:24 AM by rickharp »