Trap in Dryer Duct

[retire09]

I have disallowed a number of dryer duct installations that went down below the floor framing and then back up to exit above grade creating a long horizontal trap in the duct.

I would think this would hold moisture and lint and should not be allowed by code but I am unable to find any specific language that would disallow it othe than the limitation on length due to all the 90s.

Am I wrong in disallowing this type of installation?

 

[fatboy]

Nothing in the code prohibits it, other than length and number of fittings........

 

[mjesse]

I don't believe there is Code language to back your claim. Any horizontal run may have the same issue regardless of it's location above or below a floor.

There is this from the 2009 IMC - 504.3 Cleanout. Each vertical riser shall be provided with a means for cleanout.

 

[retire09]

Is there no concern over the trap in the duct holding moisture or lint?

I know there is no requirement to slope the duct to drain but it seems a trap in the duct would be a potential problem.

 

[retire09]

Is there no concern over the trap in the duct holding moisture or lint?

I know there is no requirement to slope the duct to drain but it seems a trap in the duct would be a potential problem.

Also, the IRC M1502.4.4.1 limits the length to 25' but the IMC 504.6.4.1 limit is 35'. Why is there a difference?

 

[mjesse]

Is there no concern over the trap in the duct holding moisture or lint?

You may be over-thinking it. A plumbing "trap" works because water remains in a pipe to prevent sewer gas backup.

Just because a duct looks like a trap, doesn't make it a "trap".

Lint will build up in the duct no matter its shape or direction. My home has a 10' horizontal run to one 90, followed by 6" horizontal. I need to clean it out at least once per year due to build-up. It's the nature of the beast.

Also, the IRC M1502.4.4.1 limits the length to 25' but the IMC 504.6.4.1 limit is 35'. Why is there a difference?

Good catch I don't have an answer for you, but it has been mentioned before.

 

[steveray]

2012 IRC is 35.....dryer fires don't matter anymore, your house is sprinklered....

 

[north star]

~ | ~ | ~



From the `12 IRC, Section M1301.1- Scope: "The provisions of this chapter shall govern

the installation of mechanical systems not specifically covered in other chapters applicable

to mechanical systems............Installations of mechanical appliances, equipment and systems

not addressed by this code shall comply with the applicable provisions of the International

Mechanical Code and the International Fuel Gas Code."



From the `12 IMC, Section 504.1- Installation: "Clothes dryers shall be exhausted in

accordance with the manufacturer’s instructions..........Dryer exhaust systems shall be

independent of all other systems and shall convey the moisture and any products of

combustion to the outside of the building."



IMO, ...if your "long horizontal run" has created a trap for condensation

& lint to collect, then the ducting install is not compliant.......It does not

convey [ completely ] the exhaust products to the exterior of the structure.



~ | ~ | ~

 

[Francis Vineyard]

A reminder the ICC Fuel/Gas, ICC Mechanical, the IRC Fuel/Gas and IRC Mechanical can result in inconsistencies with each having a separate code committee. I believe the 2009 IRC extended exhaust duct for gas dryers to 35 ft but not for Mechancal; electric and fuel oil dryers. Will find the same difference with the fasteners in dryer duct between editions of the ICC and IRC.

 

[JBI]

2015 IRC allows up to 35' with reductions for fittings, also allows manufacturers specs to be used, another sub-section addresses power vents, and lastly requires tagging for runs over 35'.

Since this I covered in the IRC, no need to use the IMC.