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Drawing combustion air for a gas dryer

Can you tell me where the combustion air is drawn from? I have a laundry room within a bedroom and was told by the fire inspector I could not draw the air from a living space. I want to know if I can buy or fabricate a duct to draw air from an alternative area such as the attic. He told me I caould have the dryer there if I can could draw the air from the attic.

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  • Anonymous Oct 07, 2008




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I am assuming that this is a gas dryer not an electric dryer.
Per the 2009 Uniform Mechanical Code Section 902.0
(B) Gas utilization appliances shall not be installed so its combustion, ventilation, and dilution air are obtained only from a bedroom or bathroom unless the bedroom or bathroom has the required volume in accordance with Section 701.2. [NFPA 54:10.1.2]
Section 701.2 basically says you need to provide adequate combustion air. One way is if the volume of the space is 50 cubic feet per 1000 btu. I personally think it is a bad idea to obtain combustion air from a bedroom even if it has adequate volume; it used to be prohibited by the Uniform Mechanical Code. The combustion air requirements are based on the BTUs of the appliance not the CFM. For gas pipe sizing purposes the Uniform Plumbing Code says that clothes dryers have a BTU input rating of approx. 35,000 BTUs. One 4" duct to the attic with the opening of the duct inside the closet within 12 inches of the ceiling would provide enough combustion air per the "One Permanent Opening Method" in UMC chapter 7.

Make up air is a different requirement than combustion air. Chapter 5 of the UMC states that if you have a dryer in a closet you need to provide a make-up air opening of 100 sq inches. The make -up air is to replace the air that is being exhausted not to provide air for combustion. The make -up air could be taken form the exterior of the building or another room within the building. Technically the closet should be insulated and weatherstripped if you get the make-up air and combustion air form the exterior.

Sorry doc john but the fire inspector is not talking about the exhaust duct (environmental air duct). That is required no matter where you have installed the dryer and is a totally separate

Posted on Oct 05, 2010

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The inspector is correct about the make-up air or combustion air. Most appliances, and definitely fuel burning appliances, require fresh air to offset the discharged air that comes, in your case, from the clothes dryer exhaust (where the lint discharges).
THat air needs to come from either a room that is not a bedroom or bathroom or from the outside or from a combination of both. The room for the combustion air needs to be 50 cubic feet per 1000 btu of aggregate input air.
The easier way is to often have a duct to the outside. A typical gas dryer requires 150 CFM of combustion air, which you can achieve through a 6" round pipe.

Posted on Nov 25, 2008

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HI, thanks for the question. you are not drawing air, with the vent from the dryer. you are blowing air to the outside. and cannot be vented to the attic. must go to the outside . thanks the appliance doc.please rate my answer.

Posted on Oct 07, 2008

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