The instaler and getting a written load calculation are the most
inportant as it is so easy for an installer to oversize you. Larger
units cost more, oversize and you wont remove humidity and heat to
quickly-unevenly. 80% is for areas that don`t have heat as a main
portion of their bill as Carrier has furnaces that are 16% more
efficient. Are you sure the Carrier is a VS motor and not 2 speed. You
did not say where you live and realy need more than 2 bids and a load
calculation.