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Dryer duct joint connection methods

Coder

Coder

Silver Member
Joined
Nov 15, 2011
Messages
302
Location
Colorado
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?
 
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
 
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.
 
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.
 
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.
 
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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Agree as long as the high temp limit switch does not fail

th


th


Use the proper piping

th
 
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.
 
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.
 
"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.
 
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?
 
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.

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