The sizing of the air conditioning unit for a particular house cannot be accurately given until a heat loss and gain calculation is performed. The load calculation, as it is typically called, takes into account many factors such as total square footage of the house, wall construction and insulation values, and roof construction and insulation values. The load process is too complicated to allow a quote over the phone. A representative will need to go to your home and collect the data and quote the size and equipment you want.