warm upstairs, cool down...should I change my return design?

homey6660

I just had the AC installed and I went with two returns--one on each level of my 1600 sq ft house. RIght now, the ducts are still exposed b/c the contractor is working with me to fine tune the install based on how it's been operating.

The first floor gets cool very quickly and easily. The return is pulling a lot of air, based on my hold-a-papertowel-in-the-return-and-watch-it-flutter test. The return upstairs pulls less so and it is much warmer upstairs (split system wasn't doable, so I have to figure out how to make do with what I have). Now, as far as I know, there are three reasons for it being warmer upstairs...

1. it's further from the source, so it's inevitably going to be pushing less cool air to the far reaches of the duct line.

2. b/c the ducts are exposed and the registers are not on, a lot of the air is blowing out the lower level--more than it would if there were registers.

3. size of the returns (and this is my real question). I had a 2nd contractor come in to take a look and he suggested that the ducting where it connects with the blower should be narrower for the 1st floor return than it is for the 2nd floor return (right now, they're both 10 inches). His rationale is that if the return is going to pull the same amount of air, if you restrict the one on the 1st floor, it will allow more air to be pulled from the 2nd floor. Do you guys agree?

bob22

I"m no pro but whatever you do, get this fixed now otherwise you will regret it later (I live in a house with a 5 degree up vs. down difference and it stinks!). I don't think you try to starve the down to serve the up on the return side; I believe the supply and returns have to be balanced so the supply air pressure roughly equals the return air negative pressure for each room served. Some pro here will help or get a third opinion (pay for it now or later).
Let us know what happens; perhaps your fix will help others like moi.
Thanks,,
Bob

ridgevilleac

Never restrict returns. Always balance your supply air with dampers. This can be done with the defusers (registers) or inline dampers. The latter is the best way so as to keep permanant settings per room. A good contractor can figure how much cfm is needed per room. Of course the best solution you say is unatainable. A two story house is best served by two units.

biggles

the air is finding its easiest way out for now onto the first floor.with all the discharge registers in and the 1st and 2nd floors balanced it will all line up.for now get some scrap 3/4 plywood and cut it up to just bigger then the openings go around on the first floor and drop one on each register opening 1/2 covering the opening.that restriction will force the air up into the 2nd level ...to test it only the 2nd floor isnt return because you have no discharge.with the first floor open as it is block the 1st floor return and feel that air race up to the 2nd floor return which is considered cooling with the return...just to see how the air moves around...your sta location should be mounted near the first floor return nose high

homey6660

I think what I will do is keep the returns the same size. Instead, I will manipulate the vents (e.g. -- close at least some of the vents on the colder, lower level, while using a filter or some other material to limit the intake on the lower return...which would allow the upstairs return to pull more. How's that sound?

biggles

a couple of sheets of your daily newspaper over the return work fine...just visualize that return going up the stairs to the 2nd floor return