# Building Vent Sizing



## retire09 (Nov 8, 2014)

The UPC requires the aggregate area of all vents to equal the minimum size building drain.

A single bathroom with a toilet, lav and tub within a building only requires a 2" vent to service all fixtures so what is the logic in requiring a building with only one bathroom to have a 3" vent?

Does this same requirement exist in the IPC?


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## steveray (Nov 8, 2014)

IPC Vent sizing....

916.2 Vents other than stack vents or vent stacks. The diameter of individual vents, branch vents, circuit vents and relief vents shall be at least one-half the required diameter of the drain served. The required size of the drain shall be determined in accordance with Table 7 10.1(2). Vent pipes shall not be less than 11/4 inches (32 mm) in diameter. Vents exceeding 40 feet (12 192 mm) in developed length shall be increased by one nominal pipe size for the entire developed length of the vent pipe. Relief vents for soil and waste stacks in buildings having more than 10 branch intervals shall be sized in accordance with Section 914.2.


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## mtlogcabin (Nov 8, 2014)

> what is the logic in requiring a building with only one bathroom to have a 3" vent?


In your climate like mine a 2" vent could frost/ice over in the winter months


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## JBI (Nov 13, 2014)

retireo9,

The requirement is for a 3" penetration through the roof. The vent can be 2" up to 18" below the roof deck and then bump out to 3".

The reason as shown above is for frost closure.


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## penneyeugene (Jan 3, 2015)

Is there a Uniform Building Code that says that dryer exhaust vents MUST be 4 inches in diameter? I'm renting a house that has a 3 inch exhaust and the new dryer manual says do not install on less than 4 inch diameter exhaust. Please help


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## TJacobs (Jan 3, 2015)

penneyeugene, follow the manufacturer's instructions, or check with the local building department.


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## cda (Jan 3, 2015)

penneyeugene said:
			
		

> Is there a Uniform Building Code that says that dryer exhaust vents MUST be 4 inches in diameter? I'm renting a house that has a 3 inch exhaust and the new dryer manual says do not install on less than 4 inch diameter exhaust. Please help


This is from the 2009 international me mechanical code, need to check what Austin has adopted

""""

504.6.1 Material and size. Exhaust ducts shall have a smooth interior finish and shall be constructed of metal a minimum 0.016 inch (0.4 mm) thick. The exhaust duct size shall be 4 inches (102 mm) nominal in diameter.

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504.6 Domestic clothes dryer ducts. Exhaust ducts for domestic clothes dryers shall conform to the requirements of Sections 504.6.1 through 504.6.7.

504.6.1 Material and size. Exhaust ducts shall have a smooth interior finish and shall be constructed of metal a minimum 0.016 inch (0.4 mm) thick. The exhaust duct size shall be 4 inches (102 mm) nominal in diameter.

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.

504.6.3 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.

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.

504.6.4.1 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 504.6.4.1.

TABLE 504.6.4.1 DRYER EXHAUST DUCT FITTING EQUIVALENT LENGTH


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## cda (Jan 3, 2015)

penneyeugene said:
			
		

> Is there a Uniform Building Code that says that dryer exhaust vents MUST be 4 inches in diameter? I'm renting a house that has a 3 inch exhaust and the new dryer manual says do not install on less than 4 inch diameter exhaust. Please help


Did you just rent the house or have you been in it awhile????

http://www.abcb.gov.au/about-the-national-construction-code/the-building-code-of-australia

Have not found the codes free on line yet


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## mtlogcabin (Jan 4, 2015)

The length of the dryer vent pipe will be a big factor. I have seen and installed 3" dryer vents where the dryer was located on the outside wall and the vent pipe was no more than 12 inches long. This was in the early seventies.

The area of a 3 inch vent is 44% smaller than a 4 inch vent.This means that using a 3 inch vent allows only slightly more than half the amount of recommended airflow required by your dryer. It is possible your dryer will shut down on thermal overload thus making your drying time longer and aless efficient unit.

If this is a gas dryer I would change the duct to 4 inch


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## cda (Jan 4, 2015)

Forgot about the good old days

Aussie

If the dryer vent met code when installed in away it is legal

But maybe with modern dryers they need bigger vent opening , which is not a code issue in away


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