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I have a 5 ton Trane split system that puts out 2150 cfm and it does not seem to heat the house and runs constantly, air temperature at all the supply vents is around 100 degrees. I'm concerned that the return air boxes are not sized correctly. There are 2 ceiling mounted flex duct returns 1 is 18" and the other is 12". The return air box is 12" wide by 28" long for the 18" duct and 12" x 23" for the 12". Return air for the 18" duct whistle and air movement can be felt directly underneath it. The 12" return air makes little noise and no breeze is felt. Both have grills that are pretty restrictive however with a clean air filter and open grills little changes. What am I missing? Thanks so much. Scott
 

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I have a 5 ton Trane split system that puts out 2150 cfm and it does not seem to heat the house and runs constantly, air temperature at all the supply vents is around 100 degrees. I'm concerned that the return air boxes are not sized correctly. There are 2 ceiling mounted flex duct returns 1 is 18" and the other is 12". The return air box is 12" wide by 28" long for the 18" duct and 12" x 23" for the 12". Return air for the 18" duct whistle and air movement can be felt directly underneath it. The 12" return air makes little noise and no breeze is felt. Both have grills that are pretty restrictive however with a clean air filter and open grills little changes. What am I missing? Thanks so much. Scott
How many square ft. Is residence? But yes duct work to small I would want two 20 in runs of flex. Your grills should be two 24 x 48 grills or equivalent area ex: four 12x24 grills.
 
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