The contractor you use is as important as the system you buy. Make an appointment with your licensed contractor. If you don‚t have one, ask a friend for a referral or check with your local Better Business Bureau or the local chapter of the Air Conditioning Contractors of America (ACCA).* Make sure to follow these guidelines: Insist on a room-by-room load calculation using the ACCA Manual J to determine the exact amount of heating and cooling required for each room. DO NOT ACCEPT RULES OF THUMB. This calculation should be done on a computer and take into account: air-leakage rates, insulation in walls and ceilings, the size and location of doors and windows, the location of the house in relation to the sun, and external factors such as trees or overhanging porches. A precise load calculation will ensure that your system is properly sized so it delivers the comfort and efficiency you expect. Doing a precise load calculation may also save you money by avoiding the purchase of a system that's too large for your house. Ask your dealer if he sells two-stage systems equipped with a variable-speed blower motor. Ask your contractor to follow the ACCA guidelines when designing and installing your ductwork. Ask for references of others who have purchased these systems. Insist on a written cost estimate and written work contract. Inquire about product warranty and service contracts.