# Flex Duct



## Keystone (Feb 1, 2012)

I'm aware of sizing & turbulence issues with flex duct but do you see issues with using class 1 flex duct within concealed chase in a SFD from basement through two floors into attic, fire-blocking to be placed at each flr level?


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## mtlogcabin (Feb 1, 2012)

I don't know of a code restriction but personally would not

Is this the RA or SA?

Will it be in a shaft? (not required)

Is the mechanical room/equipment in the basement?

Just asking to see if others may have suggestion for eliminating the possible chimney this may create.


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## Daddy-0- (Feb 1, 2012)

Check the listing. Some of the flex duct is only approved for max 14'. This cheaper flex usually has a sticker on it listing it's limitations.


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## Keystone (Feb 1, 2012)

This was a question called in to our office, personally I was hoping I overlooked a section and had the ability to prohibit this application - its bad pratice and an easy way out that from what I've researched works the HVAC system due to turbulence, creates noise issues, etc... If I recall, I believe one of the states prohibits main flex runs, maybe NM or around that area.

The duct will be in a chase throughout the floor levels.

Not certain if the duct will come from a concealed mechanical room.

I will verify the listing as soon as the specs are recieved.


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## mtlogcabin (Feb 2, 2012)

> The duct will be in a chase throughout the floor levels


That's good news. It will help the fire get from the basement to the attic quicker.

Seriously a chase is good because you have delt with the horizontial to vertical opening at the floor levels. However any unprotected shaft will create a chimney effect.


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## Gregg Harris (Feb 2, 2012)

A flexible air connector as listed in IMC 603.6.2 can only have a maximum length of 14 feet 603.6.3 prohibits it from passing through any wall, floor or ceiling and is listed under UL181 but only has to pass 12 of the 15 tests. It does not get tested for flame rate, puncture or impact and thus limits its use.

Regular flex duct can be run vertically but must be supported every 6 feet and straps must be a minimum of 1.5 inches wide, and even though a lot of contractors are using flex duct most do not follow the manufactures instructions for the installation,sizing and end up causing systems to fail upon delivering air to the space as needed and causing equipment failure such as compressors and heat exchangers. Most contractors are not aware of the pressure drop due to the higher friction rate of the flex over galvanized duct.

Each manufacturer of flex has there own friction rate duct calculator that must be used in sizing, just because the dimension is the same between brands does not mean they have the the same number of coils per foot.

Flex when run horizontally must be supported at a maximum interval of 5 feet and installed taught with a maximum of 1/2 in sag in between the supports to prevent additional friction loss and turbulence.


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## Papio Bldg Dept (Feb 2, 2012)

There are length limitations on the flex duct...I am referencing the 2006 IRC, Chapter 16, but I don't see anything in the factory-made duct section that would prohibit it's use, and M1301.1 states that systems not addressed by the IRC shall comply with the IMC & IFGC.  The IMC, Section 603.6, addresses the limitations of flexible air ducts and flexible air connectors.  The later has limited length of 14 feet.


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## Keystone (Feb 2, 2012)

In 2009 I-Codes, but all referenced sections can be had.

mtlogcabin - agree with chimney effect.

Gregg Harris & Papio Bldg Dept - Good information, Thanks...


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## Gregg Harris (Feb 2, 2012)

Gregg Harris said:
			
		

> A flexible air connector as listed in IMC 603.6.2 can only have a maximum length of 14 feet 603.6.3 prohibits it from passing through any wall, floor or ceiling and is listed under UL181 but only has to pass 12 of the 15 tests. It does not get tested for flame rate, puncture or impact and thus limits its use.Regular flex duct can be run vertically but must be supported every 6 feet and straps must be a minimum of 1.5 inches wide, and even though a lot of contractors are using flex duct most do not follow the manufactures instructions for the installation,sizing and end up causing systems to fail upon delivering air to the space as needed and causing equipment failure such as compressors and heat exchangers. Most contractors are not aware of the pressure drop due to the higher friction rate of the flex over galvanized duct.
> 
> Each manufacturer of flex has there own friction rate duct calculator that must be used in sizing, just because the dimension is the same between brands does not mean they have the the same number of coils per foot.
> 
> Flex when run horizontally must be supported at a maximum interval of 5 feet and installed taught with a maximum of 1/2 in sag in between the supports to prevent additional friction loss and turbulence.


I should have put this in my first post but I can not edit so;

According to the Air Diffusion Council that governs the installation of flexible duct systems states "Factory made ducts may not be used for vertical risers in air duct systems serving more than two adjacent stories.


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## Keystone (Feb 2, 2012)

Thanks Again....


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## Builder Bob (Feb 3, 2012)

Three story house? Basement, and two stories above grade?


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## Keystone (Feb 3, 2012)

2 story home with basement and attic.


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## Daddy-0- (Feb 5, 2012)

Don't you also need a metal boot or hard duct when passing through floors? I know you do for returns passing through to crawl spaces and for all duct work passing through a garage common wall.


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## Francis Vineyard (Feb 5, 2012)

The difference between _Ducts_ and _Connectors_:

The UL Listed Flexible Air _Duct_ must pass all of 15 tests in the UL 181 Standard. Air Ducts are labeled with a square or rectangular label showing their respective listing. There is no limitation on the length of runs when using UL Listed Air Ducts. 

The UL Listed Flexible Air _Connector _must pass only 12 of the 15 tests of the UL 181 tests, and is labeled with a round shaped label, which states "_for installation lengths not over 14 feet_". An installer may not increase the 14-foot limitation by using a splice between 14' sections of Air Connectors. This length limitation is set by the requirements in NFPA 90A & 90B Standards.

Air Diffusion Council





			
				Daddy-0- said:
			
		

> Don't you also need a metal boot or hard duct when passing through floors? I know you do for returns passing through to crawl spaces and for all duct work passing through a garage common wall.


*d. *When installed in a fire-rated floor/roof ceiling assembly, ducts shall conform with the design of the tested fire-resistive assembly.

*f. *Air Connectors (does not apply to Air Ducts) shall not be installed in lengths greater than 14 ft. [4.3 m] for any given run; *shall not pass through any wall, partition or enclosure of a vertical shaft with a 1 hour or more fire resistive rating; shall not pass through floors.  *Underlined is IBC not found in IRC.

Installation Requirements PDF

In concealed spaces and places where protection such as under stairs should have fire-blocking installed where penetrations are not prohibited in the IRC.

Do you allow wire and wire strip ties on bathroom exhaust ducts?

_In no case will the material contacting the duct or connector be less than 1-1/2" wide_". As in all cases, local jurisdiction has the final say in these matters. 

Francis


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## Gregg Harris (Feb 5, 2012)

Francis are you asking if a nylon tie can be used for the mechanical connection to the bathroom exhaust? The answer would be yes.

For support of the duct it would require a strap or support of a minimum of 1.5 inches wide.

Side note; since it is part of this thread technically there is a length limitation on  flexible air ducts in a vertical application between stories, maximum of two stories page 16 figure 26. There is no way to support the weight of the flex in a vertical application exceeding 20 feet. Even though it is strapped at a minimum of 6 feet in a vertical application the weight will pull loose from the upper connection. A story is generally 10 feet from the top of a floor to the top of the next in an eight foot ceiling height.


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## Francis Vineyard (Feb 5, 2012)

Gregg Harris said:
			
		

> Francis are you asking if a nylon tie can be used for the mechanical connection to the bathroom exhaust? The answer would be yes.For support of the duct it would require a strap or support of a minimum of 1.5 inches wide.


I was thinking more along the lines of romex and 1/8th inch wide wire ties.

M1601 are duct systems serving heating, cooling and ventilation equipment. I don't believe the code references specific requirements for bathroom ducts other than shall be exhausted directly to termination when it's required.

IMO there is no right or wrong answer.

Francis


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## Gregg Harris (Feb 5, 2012)

The 1/8th inch wire tie would be acceptable for the mechanical connection if it had UL181B listing but romex wire, would not be.


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## klarenbeek (Feb 7, 2012)

Francis Vineyard said:
			
		

> I was thinking more along the lines of romex and 1/8th inch wide wire ties.M1601 are duct systems serving heating, cooling and ventilation equipment. I don't believe the code references specific requirements for bathroom ducts other than shall be exhausted directly to termination when it's required.
> 
> IMO there is no right or wrong answer.
> 
> ...


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## Francis Vineyard (Feb 7, 2012)

Klarenbeek, thanks!  I'm learning again.

*M1507.1 General. *Where toilet rooms and bathrooms are

mechanically ventilated, the _ventilation equipment_



*M1601.1 Duct design. *_Duct systems _serving heating, cooling

and _ventilation equipment _shall be fabricated in accordance

with the provisions of this section


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