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Getting the most from a new HVAC system depends in large part on the load calculation the HVAC contractor conducts beforehand. HVAC systems need to be matched to the home in which they’re installed to deliver the comfort, energy efficiency and durability he manufacturer promises.

HVAC contractors conduct these calculations using computer software called Manual J. They take into account the overall energy efficiency of a structure and input these data into the software before recommending a new system. The contractor looks at:

  • Insulation levels throughout the home.
  • Air infiltration rates.
  • Energy efficiency, number, placement and size of the windows.
  • Cubic footage of the home that needs to be conditioned.
  • Overall floorplan design and layout.
  • Number of residents and their ages.
  • Preferred indoor temperatures.
  • Landscaping features.

Each of these data are input and the software returns the size, or capacity, for the system.

The load calculation is so important for sizing because equipment that’s too large or small lowers the energy efficiency of the equipment, indoor comfort, and shortens the lifetime of the new system.

Of the two, it’s better to install a new HVAC system that’s too small than too large, especially if you have a heat pump. When a system is too big, it runs in short cycles for brief periods.

A heat pump uses a compressor for both heating and cooling, which is particularly vulnerable when the system short cycles. The compressor uses the most electricity, particularly when it first starts. When it’s too big, the compressor will start more often and not have a chance to enter the middle of its cycle, when efficiency is highest.

Even with a furnace, the areas closest to the air handler may be comfortable, but rooms further away will be too cold or hot. During the summer, the air conditioner or heat pump won’t remove as much humidity, creating a less comfortable home.

Running the load calculation benefits both you and your contractor to find the best system for your home. To learn more, contact NisAir Air Conditioning and Heating, serving homeowners in Palm Beach, Martin and Indian River counties.

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