Glossary · Heating, cooling & ventilation

Manual J (ACCA load calculation)

Also called: ACCA Manual J · Manual J load calculation · ANSI/ACCA 2 Manual J

The US industry standard for calculating how much heating and cooling a house needs, room by room, so equipment can be sized correctly.

What it means

Manual J is published by the Air Conditioning Contractors of America (ACCA); the current version is the 8th edition (ANSI/ACCA 2 Manual J – 2016). It uses the home's dimensions, insulation, windows, air leakage, ducts and local design conditions to estimate peak heat loss and heat gain. ACCA says national building codes and most state and local jurisdictions require a load calculation done to Manual J.

Why it matters in an audit

Ask for the Manual J report with any heating or cooling quote: it's the evidence that the size wasn't picked by rule of thumb.

Typical numbers

Reference values with their sources. Your auditor’s report gives the figure for your own house.

What	Value	Source
Current edition	8th edition (ANSI/ACCA 2 Manual J – 2016)	acca.org ↗
Rule of thumb vs. calculation (ACCA blog, 2016)	Contractor rules of 400–600 ft² per ton vs. an average of 1,431 ft² per ton across 40 Manual J calculations	hvac-blog.acca.org ↗

Sources

Related terms

Load calculation An engineering calculation of how much heating and cooling a house needs, room by room, used to size equipment correctly.
Manual S (ACCA equipment selection) The US industry standard for choosing heating and cooling equipment whose real capacity, from the maker's data, fits the home's calculated loads.
Manual D (ACCA duct design) The US industry standard for designing and sizing a home's ducts so each room gets the airflow the heating and cooling equipment is meant to deliver.
ACCA (Air Conditioning Contractors of America) The US trade association for heating and cooling contractors that publishes the standard Manual J, S and D methods for sizing systems and ducts.
Design temperature The cold (or hot) outdoor temperature a heating or cooling system is sized for; colder than most winter days, but not the record low.
Oversizing Installing heating or cooling equipment with much more capacity than the house needs, usually from rules of thumb, not a load calculation.

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