# Dryer duct joint connection methods



## Coder

I got back from an ICC educational institute in March and the Mechanical Engineer teaching one of the classes informed us that the foil tape that we have all seen holding dryer ducts together is unlisted for that use and is bogus. He did make a good point that in concealed spaces how do you know if the glue on the tape has disinigrated from the heat of the exhaust or cleaning and whether or not the connection falls apart. The Mechanical code does not allow (that I am aware of) fasteners to protrude into the interior of the dryer duct and good luck getting the builder to pookie each joint. He did mention something about as long as the fasteners don't protrude more than 1/8" inch using rivets or screws is acceptable. Good luck seeing that detail..  So my question to you all is, now what do I do?


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## cda

did he say to use listed tape???


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## fatboy

I have never, nor would I ever in the future, ask for a listing on aluminum tape. I know the stuff sticks like crazy, and I have never seen the adhesive fail after years, like "duct" tape does.

Sounds like an instructors pet peave.

JMHO


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## Francis Vineyard

Did you fill out an instructor evaluation form at the end of class and let known that an even an engineer is entitled to an opinion and should emphasize it's not required.


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## mjesse

Foil tape, and done.


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## mtlogcabin

https://twshurtape.s3.amazonaws.com/media/UL%20Listed_SS.pdf

Maximum temperature rating is between 200 & 260 degrees F

High limit thermostats in dryers can vary from as much as 200ºF - 325ºF depending on make, model#, age

Most newer models are 200 degrees.

 Not allowing UL 181 tape is a good idea. There are other foil tapes that will meet the higher temps


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## Keystone

Is there actually a correlation betwenn UL listing standards and longevity of seal?

What about mastic, opinions or temperature data availablity?


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## Francis Vineyard

So what's the average or median dryer exhaust temperature per foot between floor/ceiling assembly; conditioned and vent crawls; attics; garage?

Manufacturer says duct tape; that's okay, no tape, that's okay too.  Just about every tape adheasive will eventually dry out.


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## Gregg Harris

504.6.2 Duct installation.

Exhaust ducts shall be supported at 4-foot (1219 mm) intervals and secured in place. The insert end of the duct shall extend into the adjoining duct or fitting in the direction of airflow. Ducts shall not be joined with screws or similar fasteners that protrude into the inside of the duct.

He was wrong on both counts.

The dryer exhaust will never see the temperature rating of the mastic on most aluminium tapes. The exhaust temperature is grteatly tempered by the wet clothing and conduction to the equipment along  mixed with ambient air.


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## mtlogcabin

> The dryer exhaust will never see the temperature rating of the mastic on most aluminium tapes. The exhaust temperature is grteatly tempered by the wet clothing and conduction to the equipment along mixed with ambient air.


Agree as long as the high temp limit switch does not fail












Use the proper piping


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## Gregg Harris

First and second picture apear to be caused by lint accumulation and fire inside of duct. The first picture has burn downstream from crimp, and if installed backwards would allow for lint accumulation allowing for fire to start at element and travel to the mass that caused the hot spot. The same for the transition in the second picture.


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## markw

Mastic yes- foil tape no. I have seen many examples of foil tape failures, installed on low pressure duct. Seen alot more failures on dryer duct- pls. dont approve it.


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## mtlogcabin

Both of these should work for a residential dryer

http://www.venturetape.com/pdfs/datasheets/3243%20-%20TDS.pdf

http://www.venturetape.com/pdfs/sellsheets/1581A_sellsheet.pdf


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## fatboy

"Mastic yes- foil tape no. I have seen many examples of foil tape failures, installed on low pressure duct. Seen alot more failures on dryer duct- pls. dont approve it."

I guess after 17 years in this jurisdiction and all our inspectors approving foil tape, duct tape, I should be seeing some failures............not.


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## mtlogcabin

http://www.pstc.org/files/public/Sloan.pdf


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## fatboy

OK, so it says that foil tape is not necessarlly listed for the connection, but the code does not require a "listed" application, it is silent. So............use nothing, vs. non-listed tape?


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## RJJ

Agree with MT. But at the same time agree with Fatboy on the foil tape.


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## mtlogcabin

I agree the tape/sealant is not required to be listed

My only concern is if there is excessive heat build up in the dryer vent pipe for what ever reason (lint build up or high temp limit switch failure) any sealant on the outside of the duct not list for the higher temps may contribute to the spread of a fire outside of the dryer duct.

Remember there are no required clearance to combustibles from a dryer duct

The tape is not in lieu of the required fasteners.

 M1502.4 Dryer exhaust ducts.Dryer exhaust ducts shall conform to the requirements of Sections M1502.4.1 through M1502.4.6.

M1502.4.1 Material and size.

Exhaust ducts shall have a smooth interior finish and be constructed of metal having a minimum thickness of 0.0157 inches (0.3950 mm) (No. 28 gage). The duct shall be 4 inches (102 mm) nominal in diameter.

M1502.4.2 Duct installation.

Exhaust ducts shall be supported at intervals not to exceed 12 feet (3658 mm) and shall be secured in place. The insert end of the duct shall extend into the adjoining duct or fitting in the direction of airflow. Exhaust duct joints shall be sealed in accordance with Section M1601.4.1 and shall be mechanically fastened. Ducts shall not be joined with screws or similar fasteners that protrude more than 1/8 inch (3.2 mm) into the inside of the duct.

Under the IMC there is no requirement to seal a domestic dryer exhaust duct

How many require nail plates under the IMC or IRC?

504.6.7 Protection required.

Protective shield plates shall be placed where nails or screws from finish or other work are likely to penetrate the clothes dryer exhaust duct. Shield plates shall be placed on the finished face of all framing members where there is less than 11/4 inches (32 mm) between the duct and the finished face of the framing member. Protective shield plates shall be constructed of steel, have a thickness of 0.062 inch (1.6 mm) and extend a minimum of 2 inches (51 mm) above sole plates and below top plates.


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## Coder

I am going to continue to allow the foil tape. Although, foil tape might not hold up too well when Mr. dryer exhaust cleaner shoves a brush in there to clean the lint. Will begin to push mastic as the best method for sealing the joints. Still not too sure about rivets or screws though. Seems like a law suit in the making.


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## Coder

Coder said:
			
		

> I am going to continue to allow the foil tape. Although, foil tape might not hold up too well when Mr. dryer exhaust cleaner shoves a brush in there to clean the lint. Will begin to push mastic as the best method for sealing the joints. Still not too sure about rivets or screws though. Seems like a law suit in the making.


Edit. What harm could a couple pop rivets at each joint really do? When installed the back side is pretty much mashed flat. foil tape or mastic and a couple rivets would be fine. Just thinking out loud here. trying to come up with the best answer based on the Codes saying two different things regarding fasteners.


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## Coder

Coder said:
			
		

> Edit. What harm could a couple pop rivets at each joint really do? When installed the back side is pretty much mashed flat. foil tape or mastic and a couple rivets would be fine. Just thinking out loud here. trying to come up with the best answer based on the Codes saying two different things regarding fasteners.


2009 IRC Section (M) 1502.4.2 does not say anything about not more than an 1/8"


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## Francis Vineyard

2012 IRC says it shall be joined with screws or similar fasteners


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## Gregg Harris

2012 IRC

M1502.4.2 Duct installation.

Exhaust ducts shall be supported at intervals not to exceed 12 feet (3658 mm) and shall be secured in place. The insert end of the duct shall extend into the adjoining duct or fitting in the direction of airflow. Exhaust duct joints shall be sealed in accordance with Section M1601.4.1 and shall be mechanically fastened. Ducts shall not be joined with screws or similar fasteners that protrude more than 1/8 inch (3.2 mm) into the inside of the duct.

M1601.4.1 Joints, seams and connections.

All longitudal and transverse joints, seams and connections in metallic and nonmetallic ducts shall be constructed as specified in SMACNA HVAC Duct Construction Standards—Metal and Flexible and NAIMA Fibrous Glass Duct Construction Standards. All joints, longitudinal and transverse seams, and connections in ductwork shall be securely fastened and sealed with welds, gaskets, mastics (adhesives), mastic-plus-embedded-fabric systems or tapes.

Closure systems used to seal flexible air ducts and flexible air connectors shall comply with UL 181B and shall be marked "181 B-FX” for pressure-sensitive tape or "181 B-M” for mastic. Duct connections to flanges of air distribution system equipment shall be sealed and mechanically fastened. Mechanical fasteners for use with flexible nonmetallic air ducts shall comply with UL 181B and shall be marked 181B-C. Crimp joints for round metallic ducts shall have a contact lap of not less than 1 inch (25.4 mm) and shall be mechanically fastened by means of not less than three sheet-metal screws or rivets equally spaced around the joint.

Closure systems used to seal metal ductwork shall be installed in accordance with the manufacturer’s instructions. Round metallic ducts shall be mechanically fastened by means of at least three sheet metal screws or rivets spaced equally around the joint. Unlisted duct tape shall not be permitted as a sealant on any duct.


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## fatboy

I think there is mixing and mis-matching of systems. Are we talking about a clothes dryer exhaust, or a duct system. Different chapters, different requirements..............


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## Francis Vineyard

Different requirements for gas dryers; fasteners prohibited and sealing is silent.


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## Gregg Harris

fatboy said:
			
		

> I think there is mixing and mis-matching of systems. Are we talking about a clothes dryer exhaust, or a duct system. Different chapters, different requirements..............


Unfortunately 1502.4.2 for residential dryers instead of enhancing the article with requirements, it references 1601.4.1 for other ducts.

another poor code article that ads confusion.

2012 IFGC

[M] 614.4 Exhaust installation.

Exhaust ducts for clothes dryers shall terminate on the outside of the building and shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination. Ducts shall not be connected or installed with sheet metal screws or other fasteners that will obstruct the flow. Clothes dryer exhaust ducts shall not be connected to a vent connector, vent or chimney. Clothes dryer exhaust ducts shall not extend into or through ducts or plenums.

Both should coincide with each other


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## Francis Vineyard

In summary (refer to mtlogcabin post #18); 2012 IRC Section M1502.4.2 requires fasteners; the 2012 IMC, IFGC and 2009 Mechanical Exhaust and Fuel Gas for Dryers prohibits them.

*2015 International Mechanical Code (IMC) *

Section 504.6.2 was revised to allow domestic clothes dryer exhaust duct sections to be joined with screws or similar fasteners which do not protrude more than 1/8" into the inside of the duct. This section now coincides with the requirements in the IRC. 

Source: http://m.nahb.org/fileUpload_details.aspx?contentID=194014

Yet still prohibited for gas dryers.


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## Sifu

The 2012 code had a bit of a reversal.  Where it previously prohibited mechanical fasteners, it now requires them.

2012 IRC-M1502.4.2 "Exhaust ducts shall be sealed in accordance with section M1604.4.1 and shall be mechanically fastened."  (goes on to limit the screw protrusion into the duct to 1/8")

2009 IRC-M1502.4.2 "Ducts shall not be joined with screws or similar fasteners that protrude into the inside of the duct."

I can only assume they had some failures of duct joints using only tape or mastic, which the commentary indicates.  We are skipping the 12 and adopting the 15 next, haven't read the 15 on this subject yet.


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## Sifu

Sorry, just saw page two and realize my last post was already covered.


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## Coder

Thinking that a couple pop rivets or tiny sheet metal screws at each connection will be what I am requiring from here on out. Worried about dryer exhausts in concealed spaces falling apart with no one knowing.


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## ICE

Coder said:
			
		

> Thinking that a couple pop rivets or tiny sheet metal screws at each connection will be what I am requiring from here on out. Worried about dryer exhausts in concealed spaces falling apart with no one knowing.


I would be concerned that screws/rivets will catch lint and create a hairball the size of a cat.  How will you know how far the screws/rivets project into the duct?  If it is put together correctly, there should not be a way for it to fall apart.


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## MASSDRIVER

Cat size lint is already a problem.

It's an issue of length, and the dumbness of long vertical vents.

I would rather the design take it horizontally or down for a minimum run rather than up.

In my house every month I have to haul the weed blower into the upstairs laundry and blast all the crap out.  I checked and it's just taped up, no fasteners.

While we are at codes, can we get upstairs laundry banned too, unless there is also a downstairs too?

Thank you in advance.

Brent


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## JBI

MASSDRIVER, LOL. The trend of laundry rooms upstairs surprised me the first time someone proposed it. The prospective homeowner (an old friend) pointed out that 90% or more of the laundry was generated upstairs - clothing, bedding - hence it was a convenience as opposed to schlepping the laundry down and then up stairs again. Actually makes sense and I've considered moving mine to the top floor.


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## Francis Vineyard

JBI said:
			
		

> MASSDRIVER, LOL. The trend of laundry rooms upstairs surprised me the first time someone proposed it. The prospective homeowner (an old friend) pointed out that 90% or more of the laundry was generated upstairs - clothing, bedding - hence it was a convenience as opposed to schlepping the laundry down and then up stairs again. Actually makes sense and I've considered moving mine to the top floor.


Consider most of the time is spent on the main level and will be forced to make multiple trips to the upper level for the washing and drying cycles especially if doing several loads.

Then there's the joy of replacement and service.


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## Coder

2015 International Mechanical Code (IMC)

Section 504.6.2 was revised to allow domestic clothes dryer exhaust duct sections to be joined with screws or similar fasteners which do not protrude more than 1/8" into the inside of the duct. This section now coincides with the requirements in the IRC.

This is what I am thinking I can hang my hat on. Will be adopting the 2015 in a couple years anyways.


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## ICE

Coder said:
			
		

> 2015 International Mechanical Code (IMC) Section 504.6.2 was revised to allow domestic clothes dryer exhaust duct sections to be joined with screws or similar fasteners which do not protrude more than 1/8" into the inside of the duct. This section now coincides with the requirements in the IRC.
> 
> This is what I am thinking I can hang my hat on. Will be adopting the 2015 in a couple years anyways.





> I can hang my hat on


 the screw that sticks an inch into the duct.So then at each such inspection one must ask that a screw be removed.  Then the victim will be informed that they have used the wrong screw.  Debate will commence.  Ridicule will ensue.  Screw that.


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## mjesse

ICE said:
			
		

> Debate will commence.  Ridicule will ensue.  Screw that.


...or, don't screw it and use tape.


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## Francis Vineyard

Necessity being the mother of invention;  could be a market for dryer duct seamless locking clips or buttons.


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## Coder

Francis Vineyard said:
			
		

> Necessity being the mother of invention;  could be a market for dryer duct seamless locking clips or buttons.


How about metal hose clamps? I'm not fond of the screw method either ICE, but if it is allowed in the 2015 code then I guess it needs to be addressed (or amended out).


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## ICE

Coder said:
			
		

> How about metal hose clamps? I'm not fond of the screw method either ICE, but if it is allowed in the 2015 code then I guess it needs to be addressed (or amended out).


When it gets here it's gone.  I reckon a zip tie and tape will suffice.


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## Coder

How about threaded duct. :geek:


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## steveray

How big can you get EMT?


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