Glossary · Heating, cooling & ventilation
Manual D (ACCA duct design)
Also called: ACCA Manual D
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.
What it means
Manual D starts from the airflow each room needs and the blower's performance, then sizes the supply and return ducts to deliver it. It's ACCA's ANSI-recognized duct design method, now in its third edition. Ducts that are too small or poorly laid out can leave rooms hot or cold even when the equipment is the right size.
Why it matters in an audit
When a heat pump replaces a furnace, the existing ducts may not carry enough air, and a Manual D check shows what needs to change.