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Under-slab dryer vent

K

kyhowey

Silver Member
Joined
May 26, 2011
Messages
100
Location
Elizabethtown, Ky
Builder with a slab-on-grade floor. Someone decided to run 4" PVC under the slab for the dryer vent. HVAC inspector called me to see what I thought. Code says it must be constructed with "rigid metal duct, having smooth interior with joints running in the direction of air flow."

What do you think of PVC since it's under a concrete slab? As I type this, it looks like the HVAC inspector will let it go this time with a "don't do it again" warning. He is going to require a window well on the exterior to maintain clearance from the finished grade.
 
Why should it be okay just because in encased in concrete? It still has the potential to ignite. How do inspectors keep up with exceptions should more than one contractor that make the same mistakes over and over?

This is not only a violation of the code but the manufacturer's standards which are usually less restrictive than the code.

Apparently he's asking for forgiveness than permission.

Francis
 
kyhowey said:
Builder with a slab-on-grade floor. Someone decided to run 4" PVC under the slab for the dryer vent. HVAC inspector called me to see what I thought. Code says it must be constructed with "rigid metal duct, having smooth interior with joints running in the direction of air flow." What do you think of PVC since it's under a concrete slab? As I type this, it looks like the HVAC inspector will let it go this time with a "don't do it again" warning. He is going to require a window well on the exterior to maintain clearance from the finished grade.
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2009 IRC 1502.4.1 is very specific in stating the material requirement, but if you look at the intent for the requirement to prevent fire and build up of lint inside of the exhaust duck it makes sense. Now look at M1503.2 for Domestic kitchen Exhaust under exceptions for running schedule 40 PVC under concrete slab on grade.

I do not believe that this scenario was thought of in the code determination for material for dryers.

My contention is that if the instillation requirements in 1503.2 are followed I would approve it.
 
Rider Rick, I believe you but that is not permission or an exception to allow the violation and risk life and property.

Gregg good point but one thing that immediately comes to mind is the kitchen exhaust is opened at both ends and cooking is usually attended to whereas the dryer connection is concealed and should blockage occur the potential of fire to spread is high with the dryer unattended.

Francis
 
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it's a wet location, just like an underground conduit for conductors. imo, i don't like it. who's going to maintain it? it will clog, due to lint and moisture, thats a given.what kind of measures are being taken to prevent this from backing up with water in the event of high water ? screens are not permitted by section m1502.2, 2006 irc. what is the maximum length? i'm a big fan of UP for vent's , just because they work best that way. just because you can, doesn't mean you should. also, will the dryer manufacturer allow this in their application/installation instructions ? and, a dryer isn't a down draft range
 
I would have a problem with a screen at the end of a dryer vent but not with PVC.

I allowed PVC for ducting for bathroom exhaust fans.
 
Francis technically they are both open to atmosphere on both ends.

Consider the exception to IFGC 408.4 excluding sediment traps on illuminating appliances, ranges, cloths dryers and outdoor grills because they are manually operated rather than automatic.

If a fire is going to start in a dryer it is going to be at a point of ignition not down stream in the exhaust. The reason for requiring the metal transition and metal duct is to prevent the fire from spreading. If the exhaust where to begin to fill with lint it will happen irregardless of which smooth ducting is used. If it where to begin to build up inside of the exhaust piping the internal limits on the dryer either gas or electric will trip.
 
Greg,

Would you quote IRC M150.1 for me.

M150.1 says you can't use plastic venting from dryer to wall?
 
kyhowey,

A good meomory aid would be for the contractor to jackhammer up the

slab and replace the underground pvc piping and install above slab.

Also, the window wells typically get filled up with landscaping debris

over time, plus the well itself will function like a cystern during rain

/ snow events. What does Aaaaaahnold say, " ..bad idea!" :eek:

.

 
Rider Rick said:
Greg,Would you quote IRC M150.1 for me.

M150.1 says you can't use plastic venting from dryer to wall?
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Sorry I should have used a year before the section If you are looking at 2009 it would be M 1502.4.3 Transition Ducts the verbiage is the same

Transition ducts used to connect the dryer to exhaust shall be a single length that is listed and labeled in accordance with UL 2158 A. Transition ducts shall not be concealed within construction.
 
Greg,

In the code is there anywhere it says you can't use plastic ducting from the dryer to the wall?
 
Rider Rick said:
Greg,In the code is there anywhere it says you can't use pastic ducting from the dryer to the wall?
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In each of the sections that I sited, IFGC verbiage is" cloths dryer transition ducts used to connect duct system SHALL be metal.

The others use listed and labeled UL 2158 A
 
= = =

Yankee,

Can you please explain how a compliant metal duct can be installed

inside the pvc ducting!......I have never seen that done and want

to learn..........Thank you!

= = =
 
Greg,

So I understand you correctly in the International Fire Code a plastic flex dryer duct that is sold at Home Depot to hook up to your dryer is not to code?
 
Rider Rick said:
Greg,So I understand you correctly in the International Fire Code a plastic flex dryer duct that is sold at Home Depot to hook up to your dryer is not to code?
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Rick I did not quote the International Fire Code. They were IMC= Mechanical, IRC = Residential, and IFG= Fuel Gas.

Now to answer your question more than likely the white flex that you have found at HD does not have a UL 2158A /label/listing. 430 degrees F would be one of the factors and I would bet that if you put the vinyl tubing in an oven I doubt that it would sustain 200 degrees aside from being flamable
 
Well Thank You Greg,

I had no idea that the dryer vent plastic/vinyl flex duct are not to code and were a fire danger.
 
Gregg I agree with you, but dryer fires continue as late of 2006 statistics; albiet they are probably cause by older dryers. Wonder if ductless dryers will fare better.

Image2.jpg


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http://www.iccsafe.org/cs/codes/documents/2009-10cycle/proposedchanges/imc.pdf

http://www.iccsafe.org/cs/codes/documents/2009-10cycle/roh/imc.pdf

Dryer testing for the die hards: http://www.cpsc.gov/library/foia/foia03/os/dryer.pdf



Francis
 
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Rider Rick said:
Greg,So I understand you correctly in the International Fire Code a plastic flex dryer duct that is sold at Home Depot to hook up to your dryer is not to code?
Click to expand...
RR I presume what you're seeing is the "flexible air connector" that is advertised as fire resistant UL 181 on the same shelf next to the dryer transition ducts. This is a common mistake made with air ducts and dryer ducts and I do wonder sometimes if it's done for the vender's convenience or a product marketing strategy to group the flexible ducts together in one place.

Francis
 
Francis,

I'm going to stop by Home Depot and take a better look but I didn't know there were two difference ones.

I'm sure the air ducts are less money and I'll bet some people are hooking them to there dryers without knowing.

Rick
 
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