strange piece of ductwork in the attic

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  #1  
Old 07-30-06, 08:54 PM
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strange piece of ductwork in the attic

I have noticed that I have a strange piece of ductwork that enters the attic in my place. It sticks out of the flooring about two feet and is maybe 5 inches in diameter. When the AC or heat is on, I can feel plenty of air coming out of this hole.
Does anybody know what this might be for?
I am thinking that this should be capped, as it makes no sense to sent hot/cool air into the attic (we don't use it at all).

If I should cap it, how do I go about doing that? Do they make something for this or should I just take a piece of insulation and put it on top of the opening and seal with tape?

Thanks in advance for any advise.
 
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Old 07-31-06, 06:33 AM
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Could it be a vent for the stove / Bath ?
 
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Old 07-31-06, 06:58 AM
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Couldn't say for sure, but it is the same general area as the return air ductwork. It does not appear like a vent for the stove/bath...it looks like AC ductwork (has insulation around it).

They wouldn't have run the furnace exhaust discharge to expel in the attic, right? Wouldn't that have to come up and out of the home?
 
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Old 07-31-06, 03:00 PM
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If the air is cool then it is off the HVAC system and sombody should be shoot! Unless your home is very differnt this should not be off the HVAC system. Id turn HVAC off and turn bath and stove fans on and see if it is blowing out!
 
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Old 09-02-06, 08:17 AM
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Hey...I think I have this too. Seems crazy to me!!!

I have a 3-floor townhouse with central heat & air. The equipment is located on the ground floor. The return air vents (3 of them -- 1 on each floor) all connect into a central return shaft going back down to the first floor. At the very top of the return shaft (just inside & above the 3rd floor return vent) I have a 4-inch opening that connects to a pipe that goes right up into the attic & sticks about 6 inches about the insulation. At first I thought it was to bring in fresh air, but when I was up in the attic, I noticed that air just blows right out of the pipe & into the attic. What the heck is this for? Should I plug this thing up?
 
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Old 09-02-06, 08:29 PM
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combustion air for the furnace...using attic air.
 
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Old 09-03-06, 06:10 AM
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You should do some carefull cross-checking to ensure it is from the supply fan and not an exhaust fan or combustion air as suggested.
If it is supply air then you need to block it off.
A sheet metal supplier would have a cap to do this.
If you live in a freezing climate you need to ensure there are no air leaks from the pipe that would cause condensation to form in the attic.
 
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Old 09-04-06, 08:51 AM
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I'm 100% positive that...

this duct / tube goes from the top of the return shaft & up into the attic, where it is completely open (it sticks up above the insulation). It is not connected to any exhausts (kitchen, bathroom).

Why would you want to draw in outside attic air in through the return shaft? It seems that air is being vented into the attic vice being sucked into the return shaft. I understand that some set-ups (such as air exchangers) mix fresh outside air with stale inside air; my house does not have an air exchanger though. As for combustion air for the furnace, my utility room has 2 x vents in the walls that pull in air from the ground floor to allow for that (at least I think that is what they are for).

I'm just puzzled as to why someone would design something like this. I'm pretty sure the guys who designed my HVAC set-up were idiots. They constructed my attic HVAC distribution box (not sure I'm using the right term but it is a cube where the AC or heat goes before branching off to the various rooms on the 3rd floor) from that insulated reflective board & used duct tape to hold it together. The first time I went up there I noticed it was split open on one side & venting cold air right into the attic. Cheap SOBs.

Thanks for pitching in...any add'l ideas or thoughts?
 
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Old 09-04-06, 10:31 AM
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That box in the attic is called a plenum and a necessary component of some duct systems.
It allows for proper balancing of all the branch ductwork.
The mysterious ducts blowing in the attic could be for an unused branch or future expansion.
If the open duct is connected to the return then it may be for the addition of outside air to your home.
It might be necessary to have this in your house to provide for air change which would reduce condensation build up in colder weather.
Not where I would put it but someone might have used their own reasoning to do it this way.
 
  #10  
Old 10-13-06, 12:21 PM
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How old is your house?

Last night I figured out what the "strange pipes" in our 1916 attic are. We have a two story house. It used to have a "gravity" furnance. I think they ducted the cold air returns to the attic rather than back to the furnance. The first floor cold air returns go to the furnance. The second story cold air returns from the attic just terminate - open - about 2 feet up in the attic. I wondered what these ducts were and finally realized each one is directly above a cold air return in the room below. Now I wonder, can I cap them?? Is your house old?
 
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Old 10-13-06, 03:09 PM
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Wink

ken99 If you know for sure what they are cap them off. Some sheet metal shops will have caps to go on them or make one for you. You can plug them with insulation if you want that works also.

twitch
I noticed it was split open on one side & venting cold air right into the attic. Cheap SOBs.
This is why we use a iron on alum tape for all the duct board work . It stays on .


ED
 
  #12  
Old 10-18-06, 05:49 PM
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Thanks Ed

Thanks Ed!! I will cap them. I checked by opening the register grill in each room. The duct only goes up and the only place it can go is straight up to the attic. Each register is directly below the open duct in the attic. The heat circulation can't get any worst than it is and might get better if it is not going up into the attic and out.

Thanks again.
 
 

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