How Important Is It To Get The Right Size Of Heating And Cooling Equipment?

July 30, 2015

If you’re in the market for a new central heating and air conditioning system to help reduce energy costs, you need to understand how important it is to properly size your system. Correct HVAC sizing will improve indoor comfort and reduce costs and usage in addition to maintenance.

Because older homes were not constructed with the same air tightness as they are today, it was common to install HVAC equipment with capacity of two to four times beyond what was necessary. Yet even older houses are more air tight as homeowners have added energy-efficient windows, weather-stripping and insulation to their homes. Improvements like these help reduce heat loss in winter while and minimized heat gain in the summer.

Thus, the most common mistake today is buying a system that is too big. HVAC equipment that is too large creates large, uncomfortable temperature swings. Air conditioners don’t run long enough and cannot dehumidify the air, raising the potential for unhealthy mold growth. An oversized HVAC system will also short cycle, or start and stop frequently, resulting in more wear and tear of the equipment, leading to premature failure.

Don’t purchase HVAC equipment simply on the label that lists the BTUs of the unit,or based on a “rule of thumb” used by an HVAC contractor. These are both incorrect ways to select HVAC units. The proper way to perform HVAC sizing is through Manual J and Manual D load calculations developed by the Air Conditioning Contractors of America (ACCA). Manual J calculations look at factors such as the climate where your home is located, size, shape and orientation, number of windows and their location, number of occupants, types of home appliances and much more. Manual D calculations determine the number of ducts used in an installation.

Your home’s load, or heating and cooling requirements, are affected by all of the above factors. Make sure your contractor also assess you building’s air leakage rate and inspects seals, joints and insulation on your duct system.

When buying a new system, make sure you receive a written calculation on the sizing of the system and a contract that lists the main points of installation that includes Manual J and Manual D results, along with a written warranty detailing equipment and workmanship.


About The Author

Brody Pennell

Since 1945, Brody Pennell Heating & Air Conditioning is the committed to helping homeowners in the greater Los Angeles area experience total home comfort. In 2021, the readers of the Los Angeles Times voted Brody Pennell the Best HVAC Company in the area.

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