We're in the market for a new central a/c. We're in south Texas, in a
4-bedroom home, about 1800 sq. ft. living space, high ceilings in living
area, with a southwestern exposure. Needless to say, this house gets HOT,
and our old a/c just can't keep up.

My question is what size a/c unit should we get? I'm thinking a 4-ton, but
my stepdad says to get a 5-ton. Ok, even that large a unit would no doubt be
more cost efficient than the 20+ year old 3½-ton we have now, but do we
really need that big a unit? We will eventually be building a patio cover
and doing more landscaping near the house, but in the meantime we need to
cool this place off. Any suggestions will be greatly appreciated.