Step 1: a real load calculation
System size should come from a Manual J load calculation, which accounts for your insulation, windows, orientation, air leakage and climate. "Square feet divided by 500" rules of thumb, or simply matching the old unit's size, often lead to oversizing. Oversized systems short cycle, remove less humidity and wear out faster.
Step 2: choosing the equipment
- Single-stage: on or off. Lowest cost.
- Two-stage: runs on low most of the time. Better humidity control and quieter.
- Variable-speed (inverter): adjusts output continuously. Best comfort and efficiency, at a higher price.
Since 2023 the federal minimum for new central air conditioners is 13.4 SEER2 in Northern states and 14.3 SEER2 in Southeast and Southwest states (higher for some larger units in the Southwest).
Step 3: refrigerant and matched components
New residential systems made from January 1, 2025 use lower-impact A2L refrigerants such as R-454B or R-32 instead of R-410A. Your outdoor unit, indoor coil and line set must be compatible, and a mismatched system can lose efficiency and void the warranty. Ask whether the quote includes a new matched coil, and whether the line set will be replaced or flushed.
Step 4: the install and commissioning
- Permit pulled where required
- Old refrigerant recovered, not vented
- New pad, disconnect and whip as needed
- Brazed connections purged with nitrogen
- Pressure test and deep vacuum to below 500 microns
- Charge verified by superheat/subcooling to the manufacturer's specs
- Airflow and static pressure measured
- Thermostat set up, and warranty registered
Comparing quotes
Get at least three written quotes, and compare model numbers (including the indoor coil), SEER2 rating, warranty terms (parts and labor), what's included and payment terms. Typical full central AC replacement costs $4,000–$9,000+.
Frequently asked questions
How long does AC installation take?
A straightforward like-for-like replacement usually takes one day. Adding ductwork or changing equipment location can take two or three days.
Should I replace my furnace at the same time?
If the furnace is more than 15 years old, replacing both together often saves on labor and ensures matched airflow.
