Manual J

Metrics and Efficiency Ratings - HVAC Costs pillar

Also known as: Manual J load calculation, load calc, Manual-J

ACCA Manual J: the industry-standard residential heating and cooling load calculation. Required by code for sizing HVAC equipment; rule-of-thumb sizing is not acceptable.

Manual J is published by the Air Conditioning Contractors of America and is the standard residential load-calculation methodology referenced by the Ontario Building Code, ENERGY STAR for New Homes, and most rebate programs. It computes room-by-room heating and cooling loads in BTU/h based on insulation R-values, window U-values, infiltration rate, occupant load, and design temperatures. A proper Manual J takes 2 to 4 hours of contractor time and prevents oversizing, which causes short-cycling, humidity problems, and 10 to 20 percent higher operating costs.

See the full Ontario HVAC and home energy glossary or browse the HVAC Costs pillar.