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Flex Duct and A/C Unit Sizing

My house was built in 1960 and it is 1376 sq feet. I was told that my current AC unit is from 2003 and is a 2.5 ton. The problem is that my house is having a hard time cooling in the heat of the summer. AC companies have told me that I need at least a 3 - 3.5 ton system. ? We took out a drop-down soffit and  My husband built a new box with 6" flex tube that connects to every room. There is one flex tube per room. Is that enough?  My rooms are over 100 sq ft each. Not sure if we just need more registers to cool it more efficiently, change the size of flex tubes to larger sizes, or get a completely new unit. Please help!


    EBEBRATT-Ed Member Posts: 9,727
    If you windows and doors are decent and you have some insulation 2 1/2 tons should be ok..........depending on your location.

    No one can tell for sure without an accurate heat load done. 3-3 1/2 tons is likely too much.

    For 2 1/2 tons you need duct capacity for 1000 cfm of air. 6" flex will carry 100 cfm max. Your return(s) also have to total enough size for 1000 cfm

    Need more information.

    And the unit has to have clean air filters, and clean condenser and evaporator coils and the correct refrigerant charge