California building departments require ACCA Manual J load calculations to be submitted for all new residential construction projects. California Energy Consultants can provide you with those calculations.
HVAC residential design calculations, Manual J, Manual S, and Manual D work together:
- Manual J — Load Calculation: Determines the heating and cooling load for each room and the whole house.
- Manual S — Equipment Selection: Uses the Manual J loads to select properly sized HVAC equipment, accounting for actual performance at design conditions.
- Manual D — Duct Design: Sizes the supply/return ducts and determines airflow and static-pressure requirements to deliver the Manual J design airflow.
Calculation Process
- Manual J
- Outdoor design temperature
- Indoor design temperature/humidity
- Building dimensions and orientation
- Wall, roof, floor, window and door construction
- Window U-factor and SHGC
- Insulation levels
- Infiltration/ventilation
- Internal gains
- Room-by-room heating/cooling loads
- Required CFM by room
- Manual S
- Select furnace/heat pump/AC
- Compare equipment capacity at the actual design conditions
- Check sensible and latent capacity
- Verify heating capacity
- Account for staging/modulation where applicable
- Check blower airflow and external static pressure
- Manual D
- Start with the room-by-room CFM from Manual J
- Lay out supply and return locations
- Determine available static pressure
- Size trunks and branches
- Select duct sizes using friction rate
- Check equivalent lengths/fittings
- Verify terminal velocities and pressure losses
- Confirm total system airflow and static pressure