# Clothes dryer duct - manufacturer instructions vs. code



## MikeC (Nov 16, 2013)

I recently realized that semi-rigid ducts are not UL 2158A listed.  This is where I run into a problem.  Most manufactures allow for the use of semi rigid transition ducts, but do not allow for plastic (vinyl) or foil flexible ducts.

Both the mechanical section and the fuel gas section of the IRC read similar when dealing with clothes dryer exhaust.  First, it states that the dryer shall be exhausted in accordance with manufacturer's instructions.  Then it goes on to talk about materials, runs, equivalent lengths, etc....

Where I run into a problems is that the manufacturer's instructions say nothing of UL-2158A and allows use of a semi-rigid transition duct which doesn't meet the requirements of the code.  I have required that many flexible duct be removed and replaced with semi-rigid ducts based on what I have seen in installation instructions.  About a week ago I realized that these semi-rigid transition ducts do not meet UL 2158A.

So, how do you handle it when the code contradicts itself in M1502 and G2439?  This can also become an issue when dealing with maximum length.


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## ICE (Nov 16, 2013)

http://i1124.photobucket.com/albums/l569/ICE1000/IMG_1670.jpg


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## fatboy (Nov 16, 2013)

Don't have a code book in front of me, but the fail safe is that the most restrictive is required.


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## MikeC (Nov 17, 2013)

Fatboy, I would typically agree with you, but which is more restrictive?  The code contradicts itself by telling you to follow the manufacturer's instructions, but then telling you to use a material that will void the manufacturer's warranty.

Straight from am Electrolux manual:



> Your appliance is covered by a one year limited warranty. For one year from your original date of purchase, Electrolux willrepair or replace any parts of this appliance that prove to be defective in materials or workmanship *when such appliance is*
> 
> *installed, used, and maintained in accordance with the provided instructions*


Pretty much, IRC M1502.1 says to follow manufacturer's instructions.

Here is another contradiction:



> M1502.4.4.1 Specified length.  The maximum length of the exhaust duct shall be 35 feet (10 668 mm) from the connection to the transition duct from the dryer to the outlet terminal. Where fittings are used, the maximum length of the exhaust duct shall be reduced in accordance with Table M1502.4.4.1. The maximum length of the exhaust duct does not include the transition duct.
> 
> M1502.4.4.2 Manufacturer’s instructions.
> 
> The size and maximum length of the exhaust duct shall be determined by the dryer manufacturer’s installation instructions. The code official shall be provided with a copy of the installation instructions for the make and model of the dryer at the concealment inspection. In the absence of fitting equivalent length calculations from the clothes dryer manufacturer, Table M1502.4.4.1 shall be used.


We have a repeat in Chapter 24:



> G2439.5.5.1 (614.6.5.1) Specified length.  The maximum length of the exhaust duct shall be 35 feet (10 668 mm) from the connection to the transition duct from the dryer to the outlet terminal. Where fittings are used, the maximum length of the exhaust duct shall be reduced in accordance with Table G2439.5.5.1.
> 
> G2439.5.5.2 (614.6.5.2) Manufacturer’s instructions.
> 
> The maximum length of the exhaust duct shall be determined by the dryer manufacturer’s installation instructions. The code official shall be provided with a copy of the installation instructions for the make and model of the dryer. Where the exhaust duct is to be concealed, the installation instructions shall be provided to the code official prior to the concealment inspection. In the absence of fitting equivalent length calculations from the clothes dryer manufacturer, Table G2439.5.5.1 shall be used.


The maximum length shall be 35 feet, but the maximum length shall be determined by the manufacturer's instructions?


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## joetheinspector (Nov 17, 2013)

IMHO

Code trumps manufacturer's instructions. Otherwise the manufacturer could bypass the code adoption process simply by writing it's own instructions.

Is there anybody out there that agrees with my statement?


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## MikeC (Nov 17, 2013)

I will normally agree with that statement joe, but in this case the code tells you to follow manufacturer's instructions.  Also, manufacturer's instructions tell you that it will void the warranty if you do something different than what they want.



> M1502.1 General.  Clothes dryers shall be exhausted in accordance with the manufacturer’s instructions.





> G2439.1 (614.1) 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.


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## ICE (Nov 17, 2013)

Any dryer duct that will be concealed by construction must be installed per code.  What would apply when a new owner places a different dryer with different installation instructions?


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## Glenn (Nov 17, 2013)

MikeC said:
			
		

> I will normally agree with that statement joe, but in this case the code tells you to follow manufacturer's instructions.  Also, manufacturer's instructions tell you that it will void the warranty if you do something different than what they want.


I'm not following you here, Mike?  How would this void the warranty?

the manufacturer simply says you can use them.  The code says if you use them they have to be according to ASTM.  What's the problem?  This is why "more restrictive" is always the way to go.  Then everyone is happy (except maybe the contractor).  The manufacturer isn't saying that you can't use tested ones.

Example:

-Manufacturer says you can use: A, B, C or D

-Code says you can only use: A and C

Therefore most restrictive says you can only use A and C and all is satisfied.

Now...I can see how this situation could be problematic:

-Manufacturer says you MUST use: A or B.

-Code says you MUST use: C or D

That would be more complicated, but that's not what I'm understanding your situation to be.


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## MikeC (Nov 17, 2013)

That somewhat makes sense.  If the duct is conceal, it becomes part of the construction.  It still doesn't account for the contradiction of requirements for transition duct materials.  Just make sure no clothes dryer is installed before the final inspection is complete.  These IRC and IFGC sections need to be revisited to address these contradictions.



> What would apply when a new owner places a different dryer with different installation instructions?


The same question could be asked when replacing a category I gas appliance with a category IV gas appliance.  The vent system must be updated to meet the requirements of the new appliance.


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## ICE (Nov 17, 2013)

MikeC said:
			
		

> The same question could be asked when replacing a category I gas appliance with a category IV gas appliance.  The vent system must be updated to meet the requirements of the new appliance.


Theoretically, categorized gas appliances get more attention than a clothes dryer.  Generally, tradespeople change out furnaces.....housewives are in charge of clothes dryers and a delivery-person installs them.


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## MikeC (Nov 17, 2013)

Glenn, I have downloaded multiple clothes dryer warranties.  The all say the appliance shall be installed in accordance with the directions for warranty coverage.

The issue is that all manufacturer's I have researched require transition ducts to be material A (semi-rigid) and specifically state not to use material B or C (foil and plastic transition ducts).  IRC requires the material to meet UL 2158A.  The only product to meet this is some of the material B products, which the manufacturer has specifically stated not to use.  Add to this that IRC also REQUIRES, by the use of the word "shall", that manufacturer's instructions be followed.

To make it simple, the IRC requires two different and conflicting codes to be followed at the same time.  All of my research has lead me to believe that it is impossible to comply with both codes at the same time.


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## Uncle Bob (Nov 18, 2013)

In the 2009 IRC here are two code sections you might want to look at:  1)  R102.1  Where, in any specific case, different sections of this code specify different materials, methods of construction or other requirements, THE MOST RESTRICTIVE SHALL GOVERN.  2)  R102.4 EXCEPTION:  Where enforcement of a code provision would violate the conditions of the listing of the equipment or appliance, the conditions of the listing and manufacturer's instructions shall apply.  Please note that more restrictive code requirements DO NOT VIOLATE (lessen or negatively effect) the conditions of the listing of the equipment or appliance.  Hope this helps,  Uncle Bob


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## Fort (Nov 18, 2013)

Are you sure that your premise is correct?

That there are no UL 2158A listed semi rigid duct products available?

I just did a search and found plenty that claim the listing from various sellers, including major retailers. Is this false advertisement?


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## Gregg Harris (Nov 18, 2013)

MikeC said:
			
		

> Fatboy, I would typically agree with you, but which is more restrictive?  The code contradicts itself by telling you to follow the manufacturer's instructions, but then telling you to use a material that will void the manufacturer's warranty.Straight from am Electrolux manual:
> 
> Pretty much, IRC M1502.1 says to follow manufacturer's instructions.
> 
> ...


Mike there is no contradiction, there are two separate issues.

One is Transition Duct. IFGC 614.6.4 and IRC G2439.5.4 limiting a single  length to eight feet.

Two is the dryer exhaust duct IFGC 614.6.2 and IRC G2439.5.2 limited to 35 feet which does not include the transition duct.

A lot of transition ducts on the market do not have a UL 2158 listing and do not meet the criteria and should not be used.


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## Pcinspector1 (Nov 18, 2013)

At what point in the construction of a home do you ask to see the manufactures dryer ducting requirements? Plan review, rough-in....final?

I would think at rough-in stage it needs to meet the code unless information is provided at review that has different requirements, IMHO.

pc1


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## JBI (Nov 18, 2013)

M1502.4.4.1 and G2439.5.5.1 are default measuements to be used where the manufacturers instructions are unavailable. Hence the last sentence in both of the .2 parts.

The Codes are silent on the transition piece and only address the duct proper - the concealed part. The transition is only the (typically) short piece from the back of the appliance to the concealed duct.


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## Gregg Harris (Nov 18, 2013)

Pcinspector1 said:
			
		

> At what point in the construction of a home do you ask to see the manufactures dryer ducting requirements? Plan review, rough-in....final? I would think at rough-in stage it needs to meet the code unless information is provided at review that has different requirements, IMHO.
> 
> pc1


In most scenarios the appliance has not been chosen at rough in or even final, thus the requirements of IFGC 614 .6.5.2 AND IRC G2439.5.5.2  leading to labeling IFGC 614.6.6 and IRC G2439.5.6


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## Gregg Harris (Nov 18, 2013)

JBI said:
			
		

> M1502.4.4.1 and G2439.5.5.1 are default measuements to be used where the manufacturers instructions are unavailable. Hence the last sentence in both of the .2 parts. The Codes are silent on the transition piece and only address the duct proper - the concealed part. The transition is only the (typically) short piece from the back of the appliance to the concealed duct.


 Same verbiage in IRC G2439.5.4

614.6.4 Transition ducts.

Transition ducts used to connect the dryer to the exhaust duct system shall be a single length that is listed and labeled in accordance with UL 2158A. Transition ducts shall be a maximum of 8 feet (2438 mm) in length, and shall not be concealed within construction.


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## mtlogcabin (Nov 18, 2013)

ICE said:
			
		

> http://i1124.photobucket.com/albums/l569/ICE1000/IMG_1670.jpg


This is a UL 181 duct, it is limited to a maximum temperature of 250 degrees F. Depending on the thermal override the dryer manufacturer uses the exhaust temps could range from 200 degrees F to 350 degrees F. That is the reason the duct connector needs to be UL 2158A to meet the temperature requirements. There are numerous products that meet UL 2158A and readily available at the local hardware or the big blue or orange box stores.


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## MikeC (Nov 19, 2013)

Okay, maybe I am just reading too much into this.Here is a picture of three types of transition duct.  The top one is listed in accordance with UL2158A and appears to be foil, which is not allowed by any manufacturers that I have found.  It doesn't appear to qualify as a semi-rigid duct.  The middle is what I consider to be a semi-rigid dryer vent, which is the same as ICE posted earlier in this thread.  The is the type that I preferred to see based on what the dryer manufacturers print in their manuals.  The bottom one is obviously a cheap foil duct.

View attachment 942


View attachment 942


/monthly_2013_11/572953cf3b4e3_3-types-of-flexible-duct1.jpg.f1f83b3e20fb1155e1cbebf171fb659a.jpg


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## ICE (Nov 19, 2013)

MikeC said:
			
		

> Okay, maybe I am just reading too much into this.Here is a picture of three types of transition duct.  The top one is listed in accordance with UL2158A and appears to be foil, which is not allowed by any manufacturers that I have found.  It doesn't appear to qualify as a semi-rigid duct.  The middle is what I consider to be a semi-rigid dryer vent, which is the same as ICE posted earlier in this thread.  The is the type that I preferred to see based on what the dryer manufacturers print in their manuals.  The bottom one is obviously a cheap foil duct.
> 
> View attachment 2167


None of those qualify as dryer duct that can be concealed within construction.  I don't know anything about UL2158A but apparently it doesn't require much in the way of strength.  If the duct wall is so thin that it could be damaged by a duct brush, it's not good enough.


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## Gregg Harris (Nov 19, 2013)

MikeC said:
			
		

> Okay, maybe I am just reading too much into this.Here is a picture of three types of transition duct.  The top one is listed in accordance with UL2158A and appears to be foil, which is not allowed by any manufacturers that I have found.  It doesn't appear to qualify as a semi-rigid duct.  The middle is what I consider to be a semi-rigid dryer vent, which is the same as ICE posted earlier in this thread.  The is the type that I preferred to see based on what the dryer manufacturers print in their manuals.  The bottom one is obviously a cheap foil duct.
> 
> View attachment 2167


Can you post any manufactures that do not allow?


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## Daddy-0- (Nov 19, 2013)

Wow! Two pages on dryer ducts. Here is my take. The code allows for a maximum of 35' developed length for dryer ducts. There are some dryers that have booster fans or other means to extend their length past 35' and have undergone testing to prove that they can be used at "X" number of feet. Their maximum length is to be specified in the manufacturer's installation instructions and shall be permanently labeled at the dryer connection point so that future owners will know that they need a beefed up version also.

FWIW. We never see the connection duct at final unless it is a gas dryer. We measure the length of the dryer vent at rough in and make notes so that at final we know exactly what it is.


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## ICE (Nov 19, 2013)

Instead of UL2158A, try ULA8512.  When you are asked what that is you can tell them "That's a duct that can't be pierced with a Bic pen"


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## Daddy-0- (Nov 19, 2013)

We see the foil stuff more for short runs of bath fan duct. Remember, 14' max for these air connectors when used for bath fans etc.


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## mtlogcabin (Nov 19, 2013)




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## JBI (Nov 20, 2013)

Daddy-0- said:
			
		

> We see the foil stuff more for short runs of bath fan duct. Remember, 14' max for these air connectors when used for bath fans etc.


Citation please Daddy-O-...


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## mtlogcabin (Nov 20, 2013)

603.6.1 Flexible air ducts.

Flexible air ducts, both metallic and nonmetallic, shall be tested in accordance with UL 181. Such ducts shall be listed and labeled as Class 0 or Class 1 flexible air ducts and shall be installed in accordance with Section 304.1.

603.6.1.1 Duct length.

Flexible air ducts shall not be limited in length.

603.6.2 Flexible air connectors.

Flexible air connectors, both metallic and nonmetallic, shall be tested in accordance with UL 181. Such connectors shall be listed and labeled as Class 0 or Class 1 flexible air connectors and shall be installed in accordance with Section 304.1.

603.6.2.1 Connector length.

Flexible air connectors shall be limited in length to 14 feet (4267 mm).

Is it a duct or a connector? The only way to know for sure is to read the label


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## Gregg Harris (Nov 20, 2013)

mtlogcabin said:
			
		

> 603.6.1 Flexible air ducts.Flexible air ducts, both metallic and nonmetallic, shall be tested in accordance with UL 181. Such ducts shall be listed and labeled as Class 0 or Class 1 flexible air ducts and shall be installed in accordance with Section 304.1.
> 
> 603.6.1.1 Duct length.
> 
> ...


In response to Daddy-o's post

 I do not believe that 603.6.2.1  pertains  to a 2158A flexible dryer transition duct in an exhaust application for a bath fan since it is not a class 0 or 1 air duct as listed under UL181 testing


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## JBI (Nov 20, 2013)

mtlogcabin - Gregg is being polite... Applying the MC Chapter 6 provisions to the dryer vent is a stretch... the scope of Chapter 6 would remove the dryer vent from compliance requirements as they are covered in Chapter 5

*601.1 Scope. *

Duct systems used for the movement of air in air-conditioning, heating, ventilating and exhaust systems shall conform to the provisions of this chapter except as otherwise specified in Chapters 5 and 7.

*SECTION 504 CLOTHES DRYER EXHAUST *

*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.

*Exception: *This section shall not apply to _listed _and _labeled _condensing (ductless) clothes dryers. !--$$TAG:UPAR,,CHAPTER>D'OH!


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## mtlogcabin (Nov 20, 2013)

JBI

Agree I was just giving the max length code sections that Daddy-O  stated for bathroom exhaust. Should have been clearer in my post that it did not apply to dryer ducts.

Glad to see you are posting again. It has been a while. Hope you can get back to being a "regular" contributor again.


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## Gregg Harris (Nov 20, 2013)

mtlogcabin said:
			
		

> JBIAgree I was just giving the max length code sections that Daddy-O  stated for bathroom exhaust. Should have been clearer in my post that it did not apply to dryer ducts.
> 
> Glad to see you are posting again. It has been a while. Hope you can get back to being a "regular" contributor again.


I only tagged your post because it already had the articles listed and saved typing.


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## Daddy-0- (Dec 4, 2013)

JBI.... The bath fan "air connector" has a manufacturer's label/sticker that clearly states max allowable use is 14'. Then they sell it in 25' lengths. Haha. There is also a mechanical code section for air connectors that states the same. These connectors are typically used for bath fan vents and short runs of mechanical connections inside conditioned spaces. That is what I typically see.


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## Daddy-0- (Dec 4, 2013)

.....or you can read Mtlogcabin's code sections since I clearly did not. (They say the same thing....14' for air connectors.) sorry.


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## ICE (Dec 5, 2013)

It happened again today.


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