Let’s go to a variety of sources for the answer.
Any HVAC manufacturer’s website – let’s pick Trane because we LOVE Trane. The following is from Trane.com:
"A load calculation determines what the proper size system is for your specific home. Completed by your dealer, it factors in a number of criteria used to determine what size components you should include as part of your total comfort system, things like square footage, number of windows, and year-round weather concerns.
A load calculation is important so that your system operates at maximum efficiency, with optimum performance. Most homes have systems that are oversized, so you end up paying more than you should to heat and cool your home. Also, systems that are improperly sized tend to cycle too quickly or too slowly, and that can lead to maintenance problems, uneven temperatures, and an inability to control humidity. A properly sized system based on a correct load calculation can help ensure you enjoy long-lasting, reliable comfort whatever the season."
ACCA (Air Conditioning Contractor’s of America)
ACCA literally wrote the book on Heat Loss Heat Gain Load Calculations. It’s called Manual J and it is widely accepted in the industry as THE source for determining the proper sized HVAC equipment for your home.
The following is taken directly from ACCA’s Consumer Education series:
"Unfortunately, some contractors merely size a new system based on the old system’s capacity rather than completing a professional design. What if your home’s heating and cooling needs have changed since the last system was installed many years ago? What if the original system was not sized properly to begin with? Guess work can lead to under sizing your new system which can reduce the comfort of your home. Even worse, over-sizing will add unnecessary expense to the job’s cost and may contribute to moisture-related problems down the line.
It takes time and expertise to complete and professional load calculation and system design. Contractors lacking in the necessary technical skills or who are just interested in making a “fast buck” may try to convince you this is not important. Would you want to ride an elevator or and airplane that was not professionally designed? Quality design is important in virtually every product we use including heat and air conditioning systems.
Year-round, comfort is the goal. In the summer, you’re A/C not only cools your home’s air, it removes moisture. In the winter, your heating system must keep you comfortable without causing high utility bills. Your contractor will (all should) carefully measure your home and evaluate its levels of insulation. Windows’ sizes and quantity will be noted, levels of infiltration will be estimated and internal loads including lighting and kitchen appliances will be taken into consideration. A computerized analysis will be completed that indicates just how much heat and cooling capacity your new system should provide."
Copyright 2002 by Air Conditioning Contractors of America
For more information on ACCA, go to acca-centralohio.com
"Installing the right size equipment for the home is essential to getting the best performance and comfort. Many homeowners believe that bigger is better when buying new heating and cooling equipment. But in reality, a system that's too large will not keep your home comfortable because of frequent 'on/off' cycling. Incorrect sizing can also put stress on system components and shorten the equipment's life. To ensure proper sizing your contractor should provide a copy of the home's heat gain/loss calculations for your records."