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Sizing an HVAC system too big or too small is a recipe for inefficiency. To get the right size, a contractor has to determine cooling and heating loads, which means how much cooling or heating the home requires. There are three types of cooling and heating loads, and it's helpful to know how each one differs.

Design Load

Design load is how much heating or cooling is needed when certain conditions prevail, known as design conditions. The design conditions for Savannah and elsewhere are found in HVAC industry software called Manual J, which is used by HVAC contractors to calculate heating and cooling loads.

Calculations also include factors such as R-value of insulation, size and number of windows, and orientation and size of the home to determine requirements for cooling or heating at a particular outdoor temperature to achieve the set indoor temperature.

Extreme Load

Temperatures on the hottest and coldest days in an area are identified to determine extreme loads. However, the HVAC system would be oversized if it were designed to meet the load for these temperatures, so contractors typically calculate load requirement at just 15 to 20 percent beyond the design conditions mentioned above.

Oversizing should always be avoided. It results in short cycling, which is inefficient and keeps the system from dehumidifying the air properly.

Partial Load

Most of the year, the A/C or furnace loads are less than the design load, a condition known as partial load. That can mean that your equipment, though properly sized, is still cycling on and off too often, and not keeping the home's occupants comfortable.

One way to overcome the problems with meeting heating and cooling loads efficiently is by replacing fixed speed HVAC systems with modulating technology, or even adding a dehumidifier so a home's occupants don't feel so warm in summer.

To learn how heating and cooling loads affect your Savannah home's efficiency, check McDevitt Air's HVAC services or call 877-692-0402.

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