Great air in some vents, hardly any in others. Need advice!

Old 11-26-07, 08:01 PM
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Great air in some vents, hardly any in others. Need advice!

Hello, all. New to the forum, very impressed by the amount of info and helpful people here. Glad I found it!

My wife and I recently moved into a two-floor townhouse. It was built a year ago, but we are the first to live in it. I must start by saying, I am completely ignorant when it comes to air conditioning units, and so my apologies in advance if I leave some crucial info out or miss something obvious. Anyhow...

Our AC works great, and pumps out cold air really well. The problem is that it only sends strong air out to the downstairs vents. As we speak, the entire living room and kitchen are as cool as could be and blowing out REAL strong air. Upstairs, however, is a whole different story. I can feel SOME air (if I put my hand up to the vent) but it is almost like it is trickling out, at best. This is the case for every vent upstairs (3bdrms and 2 baths). My wife and I like to sleep in a cold house, and it is impossible to get it very cool up there at all, and it is affecting our sleep.

I spent some time browsing the forum and reading some similar threads, and came across a lot about control dampers, returns, etc... and must say, it was all a bit beyond my knowledge.

I tried shutting the vent down here in the living room the other night to see if it forced the air upstairs, and that didn't work in terms of blowing more air out up there. When I closed both vents down here (kitchen and living room) just now, the sound of the pressure makes me think it isn't good for it, so I opened one of them back up... again, even that though (both closed) doesn't put anymore air out upstairs, I went and felt them.

Reading the threads has gotten me a vague idea of what it likely is, but I guess my question is... is this something I have any chance of being able to tackle myself? COULD it possibly be something simple? Or am I likely going to need someone with more expertise to come out and look at it for me? On a current law school budget, and with my wife and I not sleeping well, needless to say we'd prefer the former.

Sorry to be so long-winded, but wanted to explain the situation well. Thanks in advance for your help. Time to head up and sleep in a warm room!

Old 11-27-07, 05:24 AM
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I call the builder and have him look at it. Your home is still under warranty and he should fix the problem.
Old 12-23-07, 09:41 PM
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Assuming the size of your unit is the right one (a load calculation would determine that), the problem you have is a balancing problem (or lack thereof).

A good cooling load calculation software should show not just how much cooling each room will need (the BTU's), but also how much air should be blown into each one of them (the CFM's). In absence of the load calculation, many HVAC professionals like using 1 cfm per square-foot of occupied space as a factor to "guesstimate" airflow needs in rooms for residential applications

Done right, balancing should include having a print-out of the airflow needs for the various rooms and be armed with a flowhood, which is a very expensive instrument that measures airflows.

A well built duct system should have a balancing damper on each branch of ductwork that taps off the supply trunk. The TAB technician measures the airflow with the flowhood and adjusts the damper position until he/she gets the CFM's the room needs.

TAB = Testing and Balancing
is the "right" way to do a job such as this one.

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