A heat load calculation is the only proper way to size equipment for a home, it takes about 6 hours to do a heat load calc. Measuring the entire house from room to room, windows, color of your roof, the direction in which the sun hits the home, insulation in walls, floors, attic, all the way down to human bodies. If you are like most people, you have hired a contractor to install a new unit and they sized it by square footage of your home. This results in greatly oversized equipment, its just a guess, and most of the time on top of that they might add a little more size “just in case”!
Well bigger is not better in air conditioning. Over sized units start and stop more frequently which increases energy costs, starting, and stopping affects longevity of equipment. Almost every service call I have ever done has been on over sized equipment and undersized ductwork. Long run times are better for the equipment, cheaper on your energy bills, and dehumidify better. You should also be aware that it takes about 15 minutes of run time before equipment gets to its Seasonal Energy Efficiency Rating, which means those short run times are much more expensive than the long ones.
Every home is different, it just makes sense that a home built in 1960 is different from a home built in 1999, even a tract home identical to the next but facing a different direction will require a different BTU (Heat) load calc.
If your not getting a printout of the heat load on your home as part of the proposal find someone that knows how to do one, and ask that they are ACCA approved calcs.
The Air Conditioning Contractors of America (ACCA) have a book for this called Manual J, we do Manuals J’s on all homes prior to installing equipment. In 2015, we reduced the size of every change out of existing equipment we did, with no complaints!
In addition to Manual J, the ACCA also has another book called Manual S, this book goes with the heat load calculation and is a sizing protocol. It would be useless to to do a heat load calculation and then just put in anything that is bigger than the numbers from the calculation. Manual S makes sure that the equipment installed is within certain percentages of the the total required BTU’s. We also do a Manual S on all jobs.