Dryer duct length

**Gary Mohel** · 05-20-2009, 06:25 AM

Looking through the summary of changes that came with my 2009 IRC it notes that the maximum length for dryer ducts has been increased from 25' to 35' however IRC M1502.4.4.1 lists the maximum length as 25'. Am I missing something or is their summary of changes incorrect?

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**Gary Burnett** · 05-20-2009, 09:01 PM

I think it can be as long as you want it as long as you hang it like this one that I inspected today.

Daniel Leung · 05-20-2009, 10:18 PM

Gary, I think the length is not a big concern, but the sagging part may form a water trap to block the airflow. (Like the one shown in your photo may be caused trouble in winter).

**Brent Crouse** · 05-21-2009, 05:07 AM

Gary,

Is that the dryer duct or a fart fan duct? Going out through the roof??? Makes a nice p-trap anyway (or is it s-trap?).

**Gary Mohel** · 05-21-2009, 05:19 AM

I have no idea where that picture came from. I was just trying to figure out why the IRC summary of changes did not match up to what the IRC manual stated concerning dryer duct length.

**Gary Burnett** · 05-21-2009, 06:45 AM

Gary M.,
I believe your summary is wrong. Some areas you can have more than the 25 feet if you add a booster fan. The fan itself in the line should be an issue but the manufacturers call it non clogging.
The picture is a dryer vent that is improperly installed with improper material. It is either a big water leak waiting to happen or a dryer fire waiting to happen......or maybe, it will be a self extinguishing dryer lint fire control system.

A.D. Miller · 05-21-2009, 09:55 AM

From the 2009 IRC:

**Jim Robinson** · 05-26-2009, 05:14 PM

I just bought a brand new dryer last week. Max length with rigid metal duct is 60 feet, with no turns. 44 feet with 2 90 degree turns, etc.

With flexible metal duct the max is 30 feet, and only 14 feet with 2 90's.

**Jerry Peck** · 05-26-2009, 05:20 PM

Originally Posted by Jim Robinson

I just bought a brand new dryer last week. Max length with rigid metal duct is 60 feet, with no turns. 44 feet with 2 90 degree turns, etc.

With flexible metal duct the max is 30 feet, and only 14 feet with 2 90's.

Jim,

GE also makes a distinction about which dryer vent cap is used, and, if two of the three models commonly available are used, the allowed length is reduced, with the given maximum lengths being based on only one exhaust cap type/style as it offers less restriction than the other two types/styles do.

**Jim Robinson** · 05-26-2009, 06:48 PM

As usual, you are correct. There are 3 vent types listed in the install instructions. It ranges from 60 to 48 feet depending on what type of vent hood is used (at the zero 90 degree turn chart). It's a pretty big range when you look at all of the recommended practices.

I'm in the clear. We have rigid metal and only one 90 degree, about 11 feet total. I'll have to go measure my hood to see what type it is. I never even thought about that aspect.