An Intro to Manuals J and D

An Intro to Manuals J and DProfessional installation of an HVAC system is “manual” labor: Manuals J and D. Published by the Air Conditioning Contractors of America, they are utilized to determine your home’s unique cooling and heating requirements — called a load calculation — and design the ductwork to convey it. Utilizing Manuals J and D (they’re actually software, not books) makes installation consistent with the current state of the HVAC art, eliminating “guesstimates.” Here’s a primer on how your HVAC contractor uses Manual J and Manual D to install cooling and heating technology.

Manual J

Every HVAC installation should be preceded by a Manual J load calculation. The HVAC contractor enters an assortment of information specific to your home gathered during a room-by-room inspection. Basic information includes characteristics of the local climate and solar exposure. Then come details of your house — every one’s slightly different — including:

  • Square footage of the home
  • Rate of air leakage
  • Amount and quality of insulation
  • Number and type of windows, as well as average daily hours of sunlight through windows
  • Type of lighting in use
  • Major home appliances
  • Number of persons living in the house

Manual J software crunches all this data into a figure in BTUs that express the heat loss and heat gain for the house. Utilizing these results, the contractor can determine the precise requirements of an A/C or furnace to keep the home at a comfortable temperature in typical summer and winter conditions.

Manual D

Manual D is software that calculates a range of variables to arrive at the most efficient, effective duct layout. The process balances the air output of the system blower in cubic feet per minute with the diameter and total length of the home’s ductwork. Other factors entered into Manual D include the friction rate generated by air moving through the ducts as well as the number of elbows, curves and joints required to construct the system.

Your source for up-to-date HVAC information since 1922, contact Paitson Bros. for more about the use of Manuals J and D.

Our goal is to help educate our customers in Terre Haute, Indiana 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 Guide or call us at 812-645-6859.

Credit/Copyright Attribution: “Mega-Pixel/Shutterstock”

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    Jeff Paitson Jeff Paitson is a third generation business owner who continues to run the business with the same values that have been passed down from previous generations since 1922.

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