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Old 07-17-2011, 01:12 PM   #1
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Return duct branch that goes outside?


There is a 8" (I'm guessing) circular duct hooked up to my furnace return, and that duct pops outside the home as the 4x8 square duct in the photo. On the inside are remnants of electrical - I'm guessing there was a fan/blower in this duct at one time. I have a modern Bryant 90i - the only thing preventing my furnace from sucking in outside air was the flimsy round ductwork valve which was bent badly, so the the last few years I was taking in some outside air anytime the furnace was on. I just sealed it up with foil tape as a short term fix.

Instead of a whole house attic fan did they have a whole house blower in the old days? I wonder why when the new furnace was put in they didn't seal this off... There's no air exchanger or filter on it, just rusty wire mesh to keep critters out and the valve on the short round duct inside to control it. Best to seal it off right?
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Old 07-17-2011, 02:09 PM   #2
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Return duct branch that goes outside?


depending on when the house was built it may be a fresh air intake for the furnace. i know in western ny they required them years ago. its so in the winter time when the furnace is running it brings in fresh outside so the air inside the house doesnt get so stale from having the house closed up all winter. it was code where i used to live and now im in ohio and the house we bought here has one also. i close the damper in the summer but open it back up in the winter. most of the time they are smaller then the regular ducting so only a small percentage of the recirculated air is from outside.

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Old 07-17-2011, 07:32 PM   #3
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Return duct branch that goes outside?


Fresh air intake. And it also means that your new furnace's exhaust is installed improperly, since that is a powered intake.
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Old 07-17-2011, 08:36 PM   #4
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Return duct branch that goes outside?


if it hooks right into the return air duct I would seal it off for now. dont need to suck any air from it when the exhaust for the furnace is right there. another case of highly qualified personell hooking up a furnace. they had to see that ductwork in the basement right next to where they ran the pvc.
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Old 07-18-2011, 07:37 AM   #5
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Return duct branch that goes outside?


Be sure you have adequate return duct opening inside the house.

Older systems may have taken a lot of outside air into the return system but nowadays this is considered energy inefficient. In addition to the outside air being warmer, the outside air is also more humid and the AC does the work of de-humidifying it. Newer systems may have an outside return air opening but this is usually automatically controlled to let in only a small amount of outside air most of the time. New residential systems usually do not have an outside return air opening, relying instead on people going in and out (the doors) to get fresh air inside.
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Old 07-23-2011, 02:33 AM   #6
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Return duct branch that goes outside?


I sealed it off for now and put a big aquarium air pump I had in the external cavity. You all can make fun of me for it but I now know per the pump's specs that 9 liters of fresh air per min are pumped directly into my furnace return duct all the
time. I'm pondering better solutions like an air exchanger/recovery unit. 9 L / min isn't much for a 2000sqft home but I figure it is an improvement over before and a quantifiable starting point I can work from. Some of my returns seem weak so I am checking into them more too related to this.

The home was built in early 1950s - at the time I'm sure it was a high quality custom built home in Peoria IL (central). Thank you all for your insights. I'm the owner of 3 yrs and didn't make the furnace/AC replacements - just workin backwards to understand things as they are.

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Last edited by Mrdippy; 07-23-2011 at 02:43 AM.
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