New A/C unit vs return duct size

[engineco16]

Our fire station had two new a/c units installed today.I have a question regarding one. I'm posting here because the station is more residential in style than commercial.

In our barracks side, which measure 30' x 18' qith another 10' x 10' room they installed a York 2 ton unit on the roof replacing the old 2 ton unit. We noticed tonight it doesn't want to cool below 72 degrees and it's in the mid 80's outside. We think the old return duct is too small at 13.5" x 15.5".

Could this be a problem and what should the proper size be? In the large room there's two 10" x 10" registers and in the small room a 10" x10". Just some general info would help us out a lot.

Thanks,
Dave

[beenthere]

Is that the size of the inside of the duct, or the size of the return grille?

[second opinion]

Our fire station had two new a/c units installed today.I have a question regarding one. I'm posting here because the station is more residential in style than commercial.

In our barracks side, which measure 30' x 18' qith another 10' x 10' room they installed a York 2 ton unit on the roof replacing the old 2 ton unit. We noticed tonight it doesn't want to cool below 72 degrees and it's in the mid 80's outside. We think the old return duct is too small at 13.5" x 15.5".

Could this be a problem and what should the proper size be? In the large room there's two 10" x 10" registers and in the small room a 10" x10". Just some general info would help us out a lot.

Thanks,
Dave

If that is the size of the return duct dimension then it is not the problem. That will handle 800 cfm at 0.06 and a velocity of 600 fpm. Not bad at all.

Was both of the indoor units replaced?

[toocoolforschool]

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[engineco16]

Is this a package unit???

If you mean a all-in-one, then yes. Everything is on the roof in one unit. The return duct tube size is 13". Still dumbfounded wny it's so slow to down. Took over four hours to cool from 73 to 69 from 7pm to almost midnight. Seems terrible to me. It b lows like hell, just doesn't cool.

[second opinion]

If you mean a all-in-one, then yes. Everything is on the roof in one unit. The return duct tube size is 13". Still dumbfounded wny it's so slow to down. Took over four hours to cool from 73 to 69 from 7pm to almost midnight. Seems terrible to me. It b lows like hell, just doesn't cool.

have them check both the airflow and charge. It should have dropped 4 degrees in one hour.

[beenthere]

How many people were in these rooms last night when you were trying to get the temp down to 69?

At 7PM, wasn't it still pretty warm outside?

[hcong]

Your duct are not undersized. How many people are in the rooms? Residential units defer because they assume not many people and there isn't any outside air requirements. Your 2 ton might be a little small if you have a lot of people in those rooms and the fact that you need outside air.

[jpsmith1cm]

toocoolforschool

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