AskCodeMan

What code or manufacture requirement determines the length or clearance of an exhaust vent roof outlet? This is especially concerning, on a dryer outlet that has restricted air flow, when installed on a barrel tile roof.

Please see attachment

Jack Wingo wrote:What code or manufacture requirement determines the length or clearance of an exhaust vent roof outlet? This is especially concerning, on a dryer outlet that has restricted air flow, when installed on a barrel tile roof.

Jack,

The clothes dryer installation instructions should show the allowed dryer duct length, which varies based on the exhaust outlet (cap/vent) hood design.

I see lint buildup on the tile, reducing the space even more.

What I don't see, though, is the pivot pint for the damper sticking out through the side of the hood, which suggests that there is no damper, and if there is not damper (which is required), then there likely is a screen (which is not allowed). Did you reach up under it with your fingers to see if the damper can easily be flicked open ('flicked open' with fingers indicates that the damper is not stuck in place and the dryer exhaust should be able to blow the damper open).

No damper brings up another potential concern ... that the exhaust hood is not made for dryer ducts. Dryer ducts need to be sealed to the exhaust hoood to that all exhaust air is discharged to the outdoors.

A proper exhaust hood will have a short piece of duct sticking down into which the dryer duct can be attached and sealed to; (like these - see notes after each link: https://www.lowes.com/pd/IMPERIAL-Black ... lsrc=aw.ds - note: this one says "Built-in backdraft damper and bird screen" and would need the bird screen removed / https://www.hvacquick.com/products.php/ ... qgQAvD_BwE - note 1: this one says "is built for the through-roof exhaust of bathroom and kitchen fans, stove vents, and intake for furnaces, fresh air makeup, and attic venting" but does not say "clothes dryers", however, it does say that it has a "removable damper", which is required for clothes dryer use, and being "removable" means it could be removed and not left in place as is required - note 2: duct adapter is "optional" ... with the end result being that this one could very easily be installed incorrectly).

This one ( https://www.homedepot.com/p/Master-Flow ... lsrc=aw.ds does not show that piece of duct at the bottom, however, if you click the video, the video shows a different style and the different style in the video does show that bottom short piece of duct to attach the dyer exhaust duct to).

Checking the inside the attic for that short neck sticking down for the dryer exhaust duct to attach to is a good indication that the through-the-roof exhaust hood is ... or is not ... for clothes dryer use (no neck to attach the clothes dryer duct to indicates that it is not made for use with clothes dryers), the neck will be attached to a bottom enclosing piece closing the exhaust hood off from the attic if the exhaust hood is intended for use with clothes dryers.

P.S. Thank you for the donation.

Jerry Peck - Codeman wrote:

Jack Wingo wrote:What code or manufacture requirement determines the length or clearance of an exhaust vent roof outlet? This is especially concerning, on a dryer outlet that has restricted air flow, when installed on a barrel tile roof.

Jack,

The clothes dryer installation instructions should show the allowed dryer duct length, which varies based on the exhaust outlet (cap/vent) hood design.

I see lint buildup on the tile, reducing the space even more.

What I don't see, though, is the pivot pint for the damper sticking out through the side of the hood, which suggests that there is no damper, and if there is not damper (which is required), then there likely is a screen (which is not allowed). Did you reach up under it with your fingers to see if the damper can easily be flicked open ('flicked open' with fingers indicates that the damper is not stuck in place and the dryer exhaust should be able to blow the damper open).

No damper brings up another potential concern ... that the exhaust hood is not made for dryer ducts. Dryer ducts need to be sealed to the exhaust hoood to that all exhaust air is discharged to the outdoors.

A proper exhaust hood will have a short piece of duct sticking down into which the dryer duct can be attached and sealed to; (like these - see notes after each link: https://www.lowes.com/pd/IMPERIAL-Black ... lsrc=aw.ds - note: this one says "Built-in backdraft damper and bird screen" and would need the bird screen removed / https://www.hvacquick.com/products.php/ ... qgQAvD_BwE - note 1: this one says "is built for the through-roof exhaust of bathroom and kitchen fans, stove vents, and intake for furnaces, fresh air makeup, and attic venting" but does not say "clothes dryers", however, it does say that it has a "removable damper", which is required for clothes dryer use, and being "removable" means it could be removed and not left in place as is required - note 2: duct adapter is "optional" ... with the end result being that this one could very easily be installed incorrectly).

This one ( https://www.homedepot.com/p/Master-Flow ... lsrc=aw.ds does not show that piece of duct at the bottom, however, if you click the video, the video shows a different style and the different style in the video does show that bottom short piece of duct to attach the dyer exhaust duct to).

Checking the inside the attic for that short neck sticking down for the dryer exhaust duct to attach to is a good indication that the through-the-roof exhaust hood is ... or is not ... for clothes dryer use (no neck to attach the clothes dryer duct to indicates that it is not made for use with clothes dryers), the neck will be attached to a bottom enclosing piece closing the exhaust hood off from the attic if the exhaust hood is intended for use with clothes dryers.

P.S. Thank you for the donation.

Jerry

I appreciate your reply, however, besides the lack of damper door, my main concern is the short height of exhaust outlets. For instance, if the vent illustrated in the attach picture, was a dryer vent outlet that has a damper door and no screen, isn't there a height issue?

Thanks Jack

PS Just finished a FABI seminar via of Zoom. These are indeed bizarre times

Jack Wingo wrote:What code or manufacture requirement determines the length or clearance of an exhaust vent roof outlet? This is especially concerning, on a dryer outlet that has restricted air flow, when installed on a barrel tile roof.

Jack Wingo wrote: ... my main concern is the short height of exhaust outlets. For instance, if the vent illustrated in the attach picture, was a dryer vent outlet that has a damper door and no screen, isn't there a height issue?

That was why I started with this part:

Jerry Peck - Codeman wrote:The clothes dryer installation instructions should show the allowed dryer duct length, which varies based on the exhaust outlet (cap/vent) hood design.

Here is a typical clothes dryer installation instruction:
https://products.geappliances.com/Marke ... 6775-4.pdf

Scroll down to page 13 of 40 and review "Exhaust Length"


Your photo shows what does not look like even the 2-1/2" vent opening height shown for short duct run installations ... meaning that it nay not have any approved duct run length - the factory (or an engineer) should determine the maximum duct run length, using the installed number of elbows in the installation. There are likely at least two 90 degree elbows (often times more, and rarely less than two).