cold air not blowing hard enough?

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Old 04-22-14, 09:13 AM
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cold air not blowing hard enough?

Hello,

I moved into a new house with a refinished basement. They have added some ducts to the basement rooms that are very short runs from the main blower motor.

My upstairs vents seem to be blowing very weak although the air is cold and measured 51 degrees. It is only 85 outside and my temp will slowly rise throughout the day even with the AC running.

I noticed some cold air leaking by the duct where the blower motor connects to the main duct work so I taped that leak. If I open the ducts in the basement close to the blower they blow VERY hard. When closing them I noticed some leaks around behind the vents so I taped those up the best I could... I still don't seem to be getting enough air upstairs. Any thoughts or ideas on how to improve or where the problem may lie?
 
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Old 04-22-14, 11:51 AM
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Did they install balancing dampers in the basement ducts? Adding more ducts to existing system without increasing CFM is a real problem. Also check the balancing dampers in your duct going upstairs.
 
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Old 04-22-14, 12:42 PM
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I cannot see any balancing dampers. I took a few photos. Maybe a home do it your selfer bad ductwork job or something? In photo one you can see 3 old small ducts heading to vents upstairs (house was built in 60). In photo 3 you can see where there is a downward duct coming right off the main duct from the furnace and this feeds two large basement rooms with the vents being very close by... Maybe a damper should be installed in this downspout? Photo 2 kind of shows how close they are to the blower.
 
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Old 04-22-14, 02:13 PM
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It appears (picture is a little dark) that there are balancing dampers on the 3 runs in the first photo. The dampers are near the furnace end of the duct (as they should be). It appears that they are wide open (again it's hard to say for certain from the picture). Usually, the damper handle corresponds with the damper position, so if the handle is parallel with the duct, the damper should be wide open.

It appears that you'll have to install a damper to limit the airflow to the basement rooms. You could probably install a single damper in the vertical duct that feeds both rooms. A better alternative would be to install two dampers, one for each room, since that would give you more control over the airflow to each of the basement rooms.
 
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Old 04-22-14, 02:16 PM
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I'd get someone that knows how to do a Manual D on your duct system, so it can be designed to deliver the required airflow to all the rooms.

Also, hope you're not using a 1" deep pleated filter as this can lower airflow.
 
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