A lot depends on the solar exposure, where you live, windows etc. Did you do a Manual J to determine load?
Manual-J Heating and Cooling Load Calculations
Manual J is the name for a specific protocol (often called “
Heat Load Calculation” or “
Cooling Load Calculation“) used to determine how much heating/cooling a home needs to stay cool and dry in the summer and warm in the winter. This load calculation process was developed by engineers in the heating and air conditioning industry and has been used for decades to accurately size heating and air-conditioning equipment. After completing this load calculation process, one can choose a properly sized piece of machinery to satisfy the load.