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Our upstairs, about 1450 sq ft, just got a new 3 ton unit put in. Our A/C guy put it in because he said the 2.5 ton unit was not enough. With the 3 ton unit in, our house is much cooler now. Now here is my questions.

We have two 16x16x16 return duct boxes. At the top of the box, there is a 10"(i think) adapter that runs flex duct to the thing with the blower( air handler?) The a/c guy said we should replace the 16x16's with a two 16x20's with 12" flex duct.

Does this make sense on what I need to do? I want to get rid of the 16x16 anyways because those filters are next to impossible to find other than online.

Next question, what is the reason for a big box for the return? why cant I have a small register at the ceiling?

Also, our upstairs consists of 3 bedrooms, living room, dining room and kitchen. Both return ducts are on opposite sides of the upper level in the hallways. All the bedroom doors in our house are always closed to keep the dogs out. Should there be any return ducts in the rooms?

We are keeping this house for a long time, so I want to get everything right and to keep the house comfortable. Any advise would be great!

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Well, if you only have 2-10" flex ducts running back to the air handler. They were too small for the 2.5 ton A/C, and are probably the reason why it couldn't cool the second floor.

2- 16X20 return grilles should be fine, and both flex ducts should be 14", not 12". Although, now that you have a 3 ton, the low air flow may be needed to keep the humidity down.

The return grilles are large so you don't hear the air being drawn through them.

If your bedroom doors aren't under cut, then a return in those rooms would help.
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