Measure the building’s square footage
Determine ceiling height and total conditioned volume
Check insulation levels in walls, attic, and floors
Evaluate window type, size, orientation, and shading
Assess air leakage and building tightness
Count occupants and estimate internal heat gains
Identify local climate zone and design temperatures
Calculate heating and cooling loads for each room
Include heat gain from appliances, lighting, and equipment
Include heat loss through walls, roof, windows, and doors
Account for duct losses and duct location
Size equipment based on calculated load, not square footage alone
Select furnace or heat pump capacity for heating load
Select air conditioner or heat pump cooling capacity for cooling load
Verify airflow requirements for the chosen system
Check blower capacity and static pressure
Size ductwork to match required airflow
Confirm refrigerant line sizing and allowable length
Consider humidity control needs
Consider zoning, sun exposure, and room-by-room differences
Use Manual J for load calculation
Use Manual S for equipment selection
Use Manual D for duct design
Have a qualified HVAC professional perform final sizing
Avoid oversized equipment
Avoid undersized equipment