What is a Manual J load calculation?
Manual J is the Air Conditioning Contractors of America (ACCA) standard for calculating how much heating and cooling a house actually needs. Instead of a square-foot rule of thumb, a Manual J looks at every room: wall, ceiling and floor insulation, window size, orientation and U-factor, infiltration, duct location, internal gains and local design temperatures.
The result is a room-by-room heat loss and heat gain — sensible and latent — that tells you what size equipment the home needs and how much air each room should receive.
Manual D duct design
Manual D takes the room airflows from the Manual J and sizes the supply and return duct system to deliver them. We account for the blower's available static pressure, fitting losses and duct lengths so each trunk, branch and register is sized to move the right amount of air quietly.
A proper Manual D is the difference between a system that keeps every bedroom comfortable and one with a hot bonus room, noisy registers and a blower working against too much resistance.
Manual S equipment selection
Manual S matches real equipment to the calculated loads using manufacturer performance data at your design conditions — not just the nameplate tonnage. That keeps furnaces, heat pumps and air conditioners from being oversized (short cycling, poor humidity control, higher cost) or undersized (can't keep up on the coldest and hottest days).
Why the code and your permit office care
The International Residential Code and the International Energy Conservation Code require heating and cooling equipment to be sized from ACCA Manual J loads and selected per Manual S, with duct systems designed per Manual D. Many building departments ask for these reports at plan review. Our packages are prepared to support that review and to line up with your REScheck envelope compliance.
Boise and most of the Treasure Valley fall in IECC climate zone 5B — cold winters, hot, dry summers — so getting both the heating and cooling side right matters.
What you get
- Room-by-room Manual J heat loss and heat gain report
- Manual D duct sizing with trunk, branch and register sizes and airflows
- Manual S equipment selection summary based on manufacturer data
- Clean PDF reports ready to submit with your permit set
- Coordination with your REScheck if envelope compliance is also needed
Who we help
- Home builders
- Architects & home designers
- HVAC contractors
- Homeowners replacing equipment
Part of our building performance in Boise, Meridian, Eagle, Nampa and Mountain Home.