American Home Inspection

The goal for a HVAC system is to provide proper air flow, heating, and cooling to each room. This sets out key criteria that describe a quality system, and key design and installation
considerations that should be met to achieve this goal. The following contains detailed information on design, fabrication, installation, and performance testing.

Be properly sized to provide correct air flow, and meet room-by-room calculated heating and cooling loads.
Be installed so that the static air pressure drop across the handler is within manufacturer and design specifications to have the capacity to meet the calculated loads.
Have sealed supply ductwork that will provide proper air flow.
Be installed with a return system sized to provide correct return air flow.
Have sealed return ductwork that will provide proper air flow to the fan, and avoid air entering the HVAC system from polluted zones (e.g., fumes from autos and stored chemicals, and attic particulates).
Have balanced air flows between supply and return systems to maintain neutral pressure in the home.
Minimize duct air temperature gain or loss between the air handler and room registers, and between return registers and the air handler.
Be properly charged with refrigerant.
Have proper burner operation and proper draft.

Procedures to Design and Install an Air Distribution System

Determine room-by-room loads and air-flows using ACCA Manual J calculation procedures (or substantially equivalent).
Layout duct system on floor plan, accounting for the direction of joists, roof hips, fire-walls, and other potential obstructions. Determine register locations and types, duct lengths, and connections required to produce layout given construction constraints.
Size duct system according to ACCA Manual D calculation procedures (or substantially equivalent).
Size HVAC equipment to sensible load using ACCA Manual S procedures (or substantially equivalent).
Install equipment and ducts according to design specifications, using installation requirements and procedures from the manufacturers' specifications. The duct system should be substantially air tight.
Charge the system appropriately, and verify charge with the evaporator superheat method or subcooling method (or substantially equivalent).
Check for proper furnace burner operation and fire-box drafting.
Test the system to ensure that it performs properly by determining that the system is properly sized,does not leak, and either has proper plenum static pressures or proper room and return airflows, and proper plenum static pressures.

HVAC (Heat/AC) System Design & Installation