On average, homeowners spend between $3,200 and $7,800 installing a central air conditioning unit. The square footage of your house, your preferred brand, and the SEER rating you select are the key variables that will impact the cost of your AC unit. You would need a 2.5 ton air conditioner for a 1,300 to 1,600 square foot home, and the unit alone would cost around $1,285 on average.