Anyone know their holes (part two)

[Bob Elliott]

Saw these two openings and never quite figured what the ducts were for.
Notice they are not circular.
Client had two like that in his other unit and never knew what they were for.

[John J. Passailaigue, Jr.]

Looks like a fresh air duct to supply fresh air to a combustable (gas water heater or gas furnace) appliance. Was there a gas appliane above the ducts?

[Jeffrey R. Pope]

I agree. . .

[Bob Elliott]

Actualy they were in the utility /laundry room.
Had two waterheaters (one for radiant heat) Hvac unit which were tied in at the flue on the right (all three to one)
other side had a dryer kitty corner and vented past the garage to out side wall.
I had no attic hatch so was left to guess
Makes sense what you guys guessed though.
I will watch for this situation in the future.
No windows in that room , and had the feel of a basement, (3 story townhouse)
Thank you

[Charley L. Bottger]

Actually I know some shi! about holes if I can think of it. Seriously though those two duct pipes are to provide combustion air (fresh air) but they are installed wrong for my area. One is suppose to be 12 inches below the ceiling and the other one is required to be 12 inches from the floor level. This creates a natural flow by allowing the warmer air at the top to exit the enclosure and the colder air flows down the longest duct to the floor. Creates air movement.</IMG>

[Bob Elliott]

Charlie I think you do know your holes.
The client mentioned that in his unit one of them was near the floor.
Damn your good.

[Dale Duffy]

Originally Posted by relliott

Charlie I think you do know your holes.
The client mentioned that in his unit one of them was near the floor.
Damn your good.

Not to start an argument Bob, (my pain pills might be working), but I agree with you, Charlie knows his holes......

[Bob Elliott]

Called my client with the news, and gave him the HOLE story.

[Dale Duffy]

Originally Posted by relliott

Called my client with the news, and gave him the HOLE story.

You tell them about your other "Hole" story also, in the plumbing dept. here?...........

[Brian A. MacNeish]

Originally Posted by cbottger

Actually I know some shi! about holes if I can think of it. Seriously though those two duct pipes are to provide combustion air (fresh air) but they are installed wrong for my area. One is suppose to be 12 inches below the ceiling and the other one is required to be 12 inches from the floor level. This creates a natural flow by allowing the warmer air at the top to exit the enclosure and the colder air flows down the longest duct to the floor. Creates air movement.</IMG>

(and from Relliot: "I had no attic hatch so was left to guess")

Sounds like this room was on the top floor of the building. If so, those pipes will be drawing air from the room most of the time due to the stack or chimney effect of warm air rising. This effect gets stronger the colder it is outside due to warm air/ cold air buoyancy differences being greater then.

If the ducts go to outdoor hoods.......on days with winds blowing against the hoods, air will be driven into the room whether needed or not. On days with the hoods in the lee of the winds, air will be sucked out of the room.

So, all in all, these passive air supplies may be both drawing air from the room most of the time. I've found most of the people who set the passive vent standards had no idea of interior or exterior house pressures and building science.

The exterior house pressure phenomenon is quite interesting. In 1998-9, a wood heat dealer in Ontario brought a video to the WETT organization showing in high wind gusts, smoke emitting from the dedicated combustion supply air duct for an airtight wood stove!! The supply air hood was in the lee of the wind and went into the main floor joist cavity to supply combustion air to a "zero clearance" stove/fireplace. The stove had a glass door and when the wind gusted, the flame would actually go down between the wood pieces as exhaust gases/smoke exited the uninsulated, regular galvanized supply air duct in the floor joists. Of course, when this happened, the chimney became the combustion air supply!!

[Bob Elliott]

Thanks Brian.
Actualy the room was off the attached Garage.

Speaking of air, I would love to have gone in the attic as this dormer pictured was up there.(but sealed off as part of the attic)


Bear in mind this is a 3 story townhouse, and that dormer must be a Gable vent. (no hatch)