Open vent in attic

Anyone know what I am seeing in the pic? It is two metal ducks about 5" diameter vented into a new townhouse attic. But from what?

Inspns 031006 036.jpg

Hi Hank,

are they bathroon vents?



My guess would be to provide combustion air, high and low, for a water heater or furnace in a closet.

Quack Quack

If they are for combustion air most likley, they should be a little higher than the inslation,

Looks like back to back exhaust vents for bathrooms. Any chance your master and guest bathrooms share the same wall run’ like in some split entry homes? That would be logical, except they should have run flexible ducts to near the roof vents to prevent moisture condensation issues in the insulation, if that’s what we’re looking at here. My 2 cents;)

Tim Brown,

If that’s what they are, I recommend they are run to the exterior.

Experience has taught me to run them under the insulation to the gable if possible to minimize condensing.

Might be different in NE.

Thanks for the feedback. I am going to recommend it be evaluated by a specialist. My training is nothing should be terminated into the attic. Wouldn’t a combustion air vent in the attic draw moist air into the furnace? Wouldn’t it better to run the combustion air vent to the outside as is normally done?

Hi Hank, these can be one of two things, one would be bathroom exhaust vent fans terminating directly into the attic instead of to the outdoors. Here in Georgia, you will see that alot on home built before the early 1990’s.

Otherwise, it is attic combustion air for one or more gas fired appliances including water heater or furnace. Section M1703.3 of the 2003 IRC states “attic ventilation shall be sufficient to provide the required volume of combustion air” and “The combustion air opening shall be provided with a metal sleeve extending from the appliance enclosure to at least 6 inches above the top of the ceiling joists and ceiling insulation.”

There are sizing requirements based on Btu/h input rating of appliances. Two openings inside the closet should be both within 12" of the top and 12" within the bottom of the enclosure. Common violations here.

Hope this helps.

Most (nearing 90%) of New Construction in SC terminates the bathroom vents in the attic space. Most via the white flexible ducting tied off to a truss member 36 inches or so above the blown in insulation…:smiley:

Those that don’t terminate in the attic run to a soffit to vent (and we all know the laws of thermodynamics apply to this setup :mrgreen: )

Fantastic Hank. Thanks much!! This was an issue in another unit by the same builder and the duck was > 12" above insulation. Thanks all for your responses. What a great way to communicate.

Hank V.

Do combustion air vents require screen mesh to prevent rodents and or vermin from entering the interior structure?

If there is a clothes dryer in the same area as a gas water heater and the area can be closed off by a door then the dryer has the potential to draw the air away from the heater and cause the flame to go out. The vent into the space above will prevent this from happening. It does not have to be high or low, it just has to be able to draw air into the area.

Did I take it that running bath exhaust to a soffit vent is a bad idea? And I’m glad to clear up that there are indeed “Metal Ducks”. I expend a lot of ammunition on these stealthy waterfowl each fall, and just KNEW they had to be armor plated…Den