Sizing Your New System: The ABC's Of Manual J

Sizing Your New System: The ABC’s Of Manual J

May 24, 2012

When HVAC contractors recommend a new air conditioner for your home, they use a tool called Manual J. Although heating and cooling equipment has consistent sizing that indicates how much it’s capable of cooling or heating, unique features of your home may necessitate more or less based on individual factors.

The terms heating load and cooling load describe what your home requires to maintain a comfortable temperature. The heating load is how much it takes to heat your home in the middle of the night under the coldest conditions. The cooling load has two components. The first, called sensible load, is the temperature at which you set your thermostat. The second is the latent cooling load and is the amount of humidity your system needs to remove when the water vapor is at its highest in your interior air, which can be substantial during the hot, humid Florida summers.

HVAC technicians also evaluate your home’s layout as part of the Manual J calculation. Open floorplans require block load analysis, while homes with many rooms are sized with room-by-room loads.

Manual J has other considerations, as well, unique to your home. These include:

  • The cubic footage of conditioned space;
  • Attic and wall insulation levels;
  • Ductwork efficiency;
  • Number of windows, their efficiency and orientation to the sun;
  • Outdoor landscaping that provides a heating or cooling buffer for the home;
  • Heat emitting appliances under roof and lighting types;
  • Preferred indoor temperatures;
  • Number of occupants; and
  • Lifestyle factors.

Air infiltration, poor insulation and incandescent lights add to your conditioning load. These are the easiest factors to improve to lower the load, which helps you choose a smaller HVAC unit, costing less initially and to operate over time. Long term improvements include thermal windows, efficient ductwork and sheltering landscaping to lower cooling costs.

Rinaldi’s Air Conditioning has provided HVAC services in the central Florida region. When you’re choosing a new HVAC system, contact us and we’ll help you accurately size your next system using Manual J, helping you save money and increase your year-round comfort indoors.

Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems).  For more information about Manual J and other HVAC topics, download our free Home Comfort Resource guide.

Rinaldi’s services Orlando, Florida and the surrounding areas. Visit our website to see our special offers and get started today!     

Buyers Guide image via Shutterstock