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When you’re buying new HVAC equipment, knowing more about the three types of heating and cooling loads used in sizing calculations can help ensure you purchase the correct capacity. The term “load” always refers to the amount of heating or cooling your Frederick, MD home requires, while “capacity” refers to specific equipment output. These are the three load types that factor into HVAC sizing calculations.

Design Load

When an HVAC professional uses Manual J to size new equipment, he inputs the design conditions, which are the local indoor and outdoor average temperatures during the summer and winter. The software uses this data and a number factors like insulation R-values and solar orientation to determine the home’s design load. Ideal design load conditions don’t exist all the time, but they provide a good guideline for sizing.

Extreme Load

Our humid subtropical climate creates some significant temperature changes throughout the year. Summer temperatures have hit 108 degrees, while the coldest winter temperature on record is -7 degrees. These variations are the extreme loads your HVAC equipment may have to handle, but they’ll occur only about 1 percent of the time.

Instead of sizing equipment using extreme loads, Manual J software pads the design conditions by 15 to 20 percent to allow for these rare occurrences. Air sealing and installing sufficient insulation are also necessary to ensure home comfort.

Part Load

The remaining 99 percent of the time, your HVAC system runs at part load, where its full capacity isn’t used. This occurs whenever the actual outdoor temperature doesn’t reach design condition temperatures. Since most HVAC equipment has a set output, this can cause excess humidity and temperature fluctuations in a home. If these are concerns, installing a whole-house dehumidifier or choosing HVAC equipment with a variable-speed compressor and air handler may be necessary to maintain comfort.

Learn more about heating and cooling loads and Griffith Energy Services, Inc.’s air conditioning installation solutions, or call us today at 888-474-3391.

Image via Flickr by nist6ss

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