What drives the price
Tonnage, efficiency rating (SEER2), and whether the air handler and coil are replaced as a matched set. Mismatched equipment loses efficiency and often voids the warranty.
Duct condition is the quiet cost. Leaky or undersized ducts cap what any new system can deliver, and a good contractor will test static pressure before quoting.
Ask for a load calculation
A Manual J load calculation sizes the system to your house — square footage, insulation, window area, orientation. Replacing like-for-like just repeats whatever mistake the last installer made.
Oversized systems short-cycle, leave the house humid, and fail early. Bigger is not better.
Before you sign
Get the model numbers of the condenser, coil, and furnace in writing, plus the labor warranty length. Check federal and utility rebates for high-efficiency heat pumps — they can be worth thousands.