A seasonal efficiency rating describes performance under its defined rating method. A particular building’s electricity use also depends on weather, load, operation, and the installed system. A rating does not directly predict the customer’s bill.
If a contractor provides an estimate, ask for the baseline, building assumptions, weather basis, energy price, and included equipment. Keep estimated cooling energy separate from the entire household’s energy use.
A before-and-after bill comparison can be informative, but changes in weather, occupancy, schedules, and other loads need consideration. Do not attribute every difference to the equipment replacement without a supported method.