What are ACCA and Manual J?

Who ACCA is. The Air Conditioning Contractors of America is a nonprofit trade association for the contractors who install and maintain heating, cooling, refrigeration, and building-performance systems. It reports about 60,000 professionals across more than 3,000 member companies. ACCA develops and publishes the technical standards for residential HVAC system design under an ANSI-accredited standards process.

What Manual J is. Manual J, Residential Load Calculation, 8th edition (ANSI/ACCA 2 Manual J-2016), is the ANSI-recognized standard procedure for producing the heating and cooling loads used to size HVAC equipment in single-family homes, townhouses, condominiums, small multi-unit buildings, and manufactured homes. The procedure specifies the design conditions and the treatment of glazing, opaque surfaces, infiltration, internal gains, duct losses, ventilation, and moisture, and the form of the result: whole-structure and room-by-room loads.

Where it is required. The International Residential Code requires that heating and cooling equipment be sized in accordance with ACCA Manual S from building loads calculated in accordance with ACCA Manual J, or by other approved methods (section M1401.3). Manual J is the only load-calculation standard the residential and energy codes reference by name. Adoption and amendment of the model codes vary by jurisdiction.

Software. ACCA licenses software that implements the procedure under the mark "Powered by Manual J." Only listed software is recognized as compliant with the standard; the list is public. ACCA's own note is that approved software does not by itself ensure an accurate calculation.

Last reviewed 2026-09-06. Accurate to the best of our knowledge as of that date. Rules change — that's why the date is there.