# Domestic clothes dryer ducts



## cda (Jul 24, 2014)

IMC 2009

504.6.4 duct length

105.2

When someone wants to do over length allowed , what proposals are you seeing and accepting??

These are going in apartment units


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## mark handler (Jul 24, 2014)

engineering or manuf data allowing more


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## cda (Jul 24, 2014)

can anyone post 2015 IMC???

or is there any changes to 2015???

504.6.4 Duct length.

The maximum allowable exhaust duct length shall be determined by one of the methods specified in Section 504.6.4.1 or 504.6.4.2.


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## fatboy (Jul 24, 2014)

What Mark said.........


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## mtlogcabin (Jul 24, 2014)

Most newer dryers will allow a greater length than the code and when a dryer duct exceeds the code maximum length we require signage placed on the wall next to the dryer duct that states the length and the dryer must be able to meet that length.

Engineering and manufacturers data is great for the original dryer but may not work for the replacement in ten years for the homeowner or the new tenant next year that brings their own 15 year old dryer.


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## mark handler (Jul 24, 2014)

Idid a lot of multifamily and custom homes in my former life,  many times the engineer upsized the ducts to 5 and 6 inches.  He did not know what unit was to be installed. Unless you put in a sub-par unit this should work with replacement units.


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## mark handler (Jul 24, 2014)

They also make dryer Duct Booster fans, though not in the code could be an alternate means and methods


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## ICE (Jul 24, 2014)

mark handler said:
			
		

> Idid a lot of multifamily and custom homes in my former life,  many times the engineer upsized the ducts to 5 and 6 inches.  He did not know what unit was to be installed. Unless you put in a sub-par unit this should work with replacement units.


Not that I would question an engineer, but increasing the diameter of the duct seems like it would slow the flow down.


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## JBI (Jul 24, 2014)

cda said:
			
		

> can anyone post 2015 IMC???or is there any changes to 2015???
> 
> 504.6.4 Duct length.
> 
> The maximum allowable exhaust duct length shall be determined by one of the methods specified in Section 504.6.4.1 or 504.6.4.2.


cda - In the 2015 IMC it is now 504.*8*.4, and there is a third subsection for power ventilators. Otherwise unchanged from 2012. (not typing the text, you'll have to wait for ICC to post the new codes, sorry)


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## Glenn (Jul 24, 2014)

ICE said:
			
		

> Not that I would question an engineer, but increasing the diameter of the duct seems like it would slow the flow down.


We require engineering for duct upsizing to increase length.  The flow does slow, and this means that more lint falls out of the flow and stays in the duct.  All engineering I have recieved has included accessible cleanouts due to the likihood of increased lint in the ductwork.


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## Yikes (Sep 4, 2014)

I concur with Glenn's experience.  When I've done multifamily apartments with longer dryer duct runs, the mechanical engineer has both upsized the duct and installed cleanouts, especially at the bottom elbow of a vertical run of duct.


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## mstehlin (Nov 25, 2014)

IMC 2009: Does the discharge for the dryer vent need to be 3' or 10' from a property line?

IMC 501.2.1.  Bath fans clearly need to be 3' from both operable windows and property lines, but does dryer discharge need to be 10'?

10' is impossible to meet in many of my projects (rehabs in zero lot line historic buildings)

3' IS allowed in the residential code, see 2009 IRC 1502.3


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## steveray (Nov 25, 2014)

504.8.4 Duct length.

The maximum allowable exhaust duct length shall be determined by one of the methods

specified in Sections 504.8.4.1 through 504.8.4.3.

504.8.4.1 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 504.8.4.1.

TABLE 504.6.4.1 504.8.4.1

DRYER EXHAUST DUCT FITTING EQUIVALENT LENGTH

DRYER EXHAUST DUCT FITTING TYPE EQUIVALENT LENGTH

4″ radius mitered 45-degree elbow 2 feet 6 inches

4″ radius mitered 90-degree elbow 5 feet

6″ radius smooth 45-degree elbow 1 foot

6″ radius smooth 90-degree elbow 1 foot 9 inches

8″ radius smooth 45-degree elbow 1 foot

8″ radius smooth 90-degree elbow 1 foot 7 inches

10″ radius smooth 45-degree elbow 9 inches

10″ radius smooth 90-degree elbow 1 foot 6 inches

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 degree = 0.0175 rad.

504.6.4.2 504.8.4.2 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 504.6.4.1 504.8.4.1 shall be used.

504.6.5 Length identification.

Where the 504.8.4.3 Dryer exhaust duct is concealed within the building construction, the

equivalent power ventilator length.

The maximum length of the exhaust duct shall be identified on a permanent label or tag. The

label or tag shall be located within 6 feet (1829 mm) of determined by the dryer exhaust

duct connection. power ventilator manufacturer's installation instructions.

504.6.6 504.8.5 Length identification.

Where the exhaust duct equivalent length exceeds 35 feet (10 668 mm), the equivalent

length of the exhaust duct shall be identified on a permanent label or tag. The label or tag

shall be located within 6 feet (1829 mm) of the exhaust duct connection.


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## mtlogcabin (Nov 25, 2014)

Your answer is found in Table 705.8 of the building code. 2009 IBC

Could be 3 ft in a sprinklered building or protected opening or 5 ft in a non sprinklered building or un-protected opening.


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