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• Under-sized or incomplete return air ducts for heating or cooling systems
• Return air adequacy
• Air Conditioning (or Heating) Duct Defects

This chapter of "How to Inspect the Central Air Conditioning or Cooling System" describes the undersized return air openings observed during inspection of the defects in return air ducts for heating or cooling systems (HVAC) such as missing air conditioning cool air supply or return air registers, undersized air conditioning duct openings, improper cooling duct routing, cooling (or heating) air duct corrosion, leaky air duct connections, defective heating or cooling ductwork materials. The photograph above shows a small HVAC return air duct located on an interior building wall. Whether or not this return air duct is adequate depends on how many such returns were installed in the building and whether or not the return air capacity is balanced with the air handler and air supply ducting. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

The master document, of which this is a chapter, describes the inspection of residential air conditioning systems (A/C systems) to inform home buyers, owners, and home inspectors of common cooling system defects. Asbestos in or on HVAC ducts is a possible hazard for which we provide links to a separate document - see "Asbestos HVAC Ducts" at below left.

Scroll down or use the links at left to continue reading about duct defects with the next section: registers and zones.

UNDERSIZED OPENINGS - Under-sized Return Air Openings/Ducts

Under-sized single central air return: when we see a comparatively small single air return in a building, such as a 12X18" grille in a ceiling or wall, we suspect that insufficient return air ducts are present. This concern is elaborated next. The photograph shows an under-sized single air return for a duct system serving an entire two story home. We increased the size of the return duct to match the air handler and observed a doubling of the air flow in the system from this single improvement! Central return air openings are very likely to be undersized when we see that the opening measurements are much smaller than the opening for air provided right at the blower fan. At another example installation, the blower fan or return air plenum opening at the furnace was 20"x18" while the return air opening at the door to the utility room was 13"x13" (reduced further in effective size by a louvered screen).

When we see amateur attempts to add supply or return air to a system, such as observation of unanticipated openings in building walls, rough-sawn door undercuts, additional openings cut in the return duct or plenum near the air handler, we suspect system design problems. It is possible that previous occupants have found that the warm air supply was not adequate. Should you confirm problems with inadequate heat delivery in some areas you'll want to consult with an HVAC engineer to make accurate measurements.

Door undercuts, central cool air return: If room doors are shut and not under-cut to permit air flow out of the room, the system's ability to cool the room may be reduced, sometimes significantly. Try running the cooling system for 10 minutes with all room doors shut. Then open a room door slightly and see what happens! When a building uses a central return air grille and doors are not undercut heating some rooms may be difficult - system cannot push cold air from the cooled or heated room back to the furnace.

While modest amounts of new duct work (to take return air from the living area) are usually not costly, extensive re-ducting of air flow may involve significant expense.

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