Manuals J and D Crucial for Proper HVAC Equipment Design, SizingYou trust your HVAC professional to correctly match your Los Angeles-area home’s new furnace or air conditioner to your heating and cooling needs. A qualified HVAC contractor uses Manuals J and D from the Air Conditioning Contractors of America (ACCA) to do the job. 


Properly sized heating and cooling equipment for your unique Los Angeles-area home means energy and money savings for years to come. Over-sized equipment and poorly designed ductwork create a cascade of issues:

  • Over-sized equipment is more costly than the correctly sized furnace at installation
  • Too large a furnace blower strains ductwork
  • Short-cycling wastes natural resources
  • Temperatures vary wildly room to room
  • Ductwork bangs and clatters
  • Short-cycling increases repair and maintenance costs
  • Ductwork loses heat in winter and cool air in summer

Manuals J and D prevent all that. Manual J calculations yield the British Thermal Units (BTUs) for heat lost in winter and gained in summer. These numbers lead your HVAC contractor to the proper duct design using Manual D. Together, Manuals J and D deliver efficient, comfortable heating and cooling.

Manual J

Manual J software calculates the heating and cooling loads. Your HVAC contractor inputs variables such as the numbers of windows and doors, square footage, insulation, number of occupants and appliances, and geography. Los Angeles homes do not demand the same heating capacities as, say, homes in Vermont.

Manual J tells your HVAC contractor not only total heating and cooling requirements, but also room-by-room needs and peak loads for each room.

Manual D

After you and your contractor have settled on the equipment to heat and cool your home, the furnace blower data is plugged into Manual D’s software program and the most efficient ductwork layout emerges. This may mean modifications to existing ductwork to improve fuel economy and provide more even heating and cooling.

Manuals J and D guide your contractor to provide you with the most efficient, most comfortable heating and cooling equipment possible. For more help with heating and cooling equipment for your Los Angeles-area home, contact us at Around the Clock Air Conditioning and Heating, Inc.

Our goal is to help educate our customers in Los Angeles, North Hollywood and surrounding areas about energy and home comfort issues (specific to HVAC systems).  For more information about Manuals J and D and other HVAC topics, download our free Home Comfort Resource guide.

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