ducts and vents on heat pump/ac system

have one story house with large loft. One intake for HVAC system is in on main (1st) floor in hall and and second is in loft (both same size). Three output vents in loft. Twelve output vents on 1st floor. Capacity of unit adequate for size of house but loft does not cool down enough in summer. No prob in winter with heat because heat rises from 1st floor. Will I tax the unit too much if I close five or six of the of the output vents on the first floor in order to force more cold air through the three output vents in the loft. Seems to me it would just make the the air move faster (more cubic feet per minute), but I don't want to risk damaging my unit by doing this.
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Frank Thompson wrote:

Likely. Someone would need to do some numbers of the system. My guess is you need more capacity of supply and likely return to the loft.
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Joseph Meehan

Dia duit
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