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• Heating & Cooling Ducts - Supply Registers & Zones
• Air Conditioning (or Heating) Duct Defects

This chapter of "How to Inspect the Central Air Conditioning or Cooling System" describes the inspection of heating and air conditioning (HVAC) duct registers & zones for defects 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 such as Goodman gray flex-duct, some Owens Corning Flex-duct, and asbestos-containing air conditioning or heating duct work.

The photograph above shows a 1930's heating and cooling air supply register still in active use, but with leakage around the register which transmitted odors and mold from the building basement. © 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 or mold in or on HVAC ducts are a possible hazards for which we provide links separate documents - see "Asbestos HVAC Ducts" at below left.

SUPPLY REGISTERS, & ZONES - Cooling Distribution Ducts, Registers, & Zones

How to Diagnose Stains at Ceiling Air Supply Registers

The ceiling air supply register shown in the photo at left is typical of modern residential installations except for those leak stains around the register.

Further investigation was needed to discover whether the stains were due to a roof leak above this point or an air conditioning leak into and around the supply duct or as we've seen in some northern climates, accumulation of condensation and even ice in ceiling air conditioning ducts caused by movement of moist air backwards through the duct system by natural convection when the HVAC system was turned off.

The ceiling register in the second photo at right has blown soot and debris onto the ceiling itself. Further investigation was needed to determine if this soiling was from failure to maintain filters in the duct system, mold or debris in the duct system, a failed (and dangerous) oil-fired or gas-fired furnace heat exchanger, or other causes.

Heating & Cooling source in each room:

The minimum air conditioning system inspection standard (or heating inspection standard) includes the observation of the presence of a cooling source in each habitable room in the building. Ductwork to each room (at least connected to visible supply registers) & supply registers themselves should be observed in every room, delivering conditioned air to each habitable room (we can exclude closets and utility rooms and in some locales, baths).

Beware of "dummy" supply registers that are not connected to anything.

Beware of supply registers that are connected to ductwork but have no air flow due to duct routing errors, pinched, or disconnected duct work, or similar faults. This defect can only be observed if conditions permit operating the system.

Placement of Supply & Return Ducts & Registers for Heating versus Cooling

In a home inspection report, cooling system duct work defects may be reported under "Heating System" for cases where same ductwork is used for both heating and cooling. However, optimal supply and return placement for cooling is different from the optimum placement for cooling supply and return air. A heating system may deliver warm air low on walls or at floor level (warm air rises).

A cooling system may prefer to deliver cool air from a supply diffuser high on the wall or in ceilings (cool air falls) and draw cool air to the system return duct from a separate high-location in a ceiling (warm air rises to the high return duct for air conditioning). This topic is discussed in more detail at LOCATION OF DUCTS below.

Heating or Cooling Zone Control for Furnaces & Central Air Conditioning Systems

Zone control for air handling systems can be provided by:

• Dampers at individual air supply registers
• Manual dampers in the duct work to permit balancing the system
• Motorized zone dampers that open or close sections of the ductwork to airflow provided by a single air handler unit
• Installation of individual air handlers to serve different building areas, typically in residential properties, upper and lower floors.

See ZONE DAMPER CONTROLS for details about how to achieve individual zone control for warm air heating for for air conditioning systems.

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

More Reading:
Asbestos as a duct hazard is discussed at ASBESTOS HVAC DUCTS.
Fiberglass in HVAC ducts is discussed at Types of Duct Work using fiberglass materials and at risk of mold contamination are discussed here.
Mold in the air handler or duct work is discussed at AIR HANDLER UNIT chapter
HOW TO PREVENT MOLD: Correct the Causes of Mold and Prevent Indoor Mold or other indoor environment problems
OPTIMUM INDOOR AIR QUALITY - Air Filter Choices & Placement for Optimum Indoor Air Quality.

Use links just below or 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.

AIR CONDITIONING SYSTEMS
AIR CONDITIONER COMPONENT PARTS
CONTROLS & SWITCHES
A/C TYPES, ENERGY SOURCES
RATED COOLING CAPACITY
AIR CONDITIONER BTU CHART
SEER RATINGS & OTHER DEFINITIONS
OPERATING COST
SYSTEM OPERATION
OPERATING TEMPERATURES
OPERATING DEFECTS
LOST COOLING CAPACITY
COMPRESSOR & CONDENSING COIL
AIR HANDLER UNIT
AIR FILTERS for HVAC SYSTEMS
CONDENSATE HANDLING
BACKUP HEAT for HEAT PUMPS
CLEANING & Legionella BACTERIA
DUCT SYSTEM DEFECTS
  ASBESTOS HVAC DUCTS
  DUCT ROUTING & SUPPORT
  BALANCING AIR DUCT FLOW
  FIBERGLASS HVAC DUCTS
  FIRE DAMPERS in DUCTWORK
  GOODMAN GRAY FLEXDUCT
  INCREASING RETURN AIR
  LEAKY DUCT CONNECTIONS
  LOCATION OF REGISTERS & DUCTS
  OWENS CORNING FLEXDUCT
  RETURN AIR REGISTERS & DUCTS
  SUPPLY REGISTERS, & ZONES
  Transite Pipe HVAC Ducts
  UNDERSIZED RETURN DUCTS
  UNSAFE DUCT OPENINGS
  VIBRATION DAMPERS
  WET CORRODED DUCT WORK
  ZONE DAMPER CONTROLS
FAN AUTO ON CONTROLS
A/C REFRIGERANTS
A/C DIAGNOSTIC FAQs
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS
CRITICAL DEFECTS
Air Conditioning "How To" Books
FURNACES WARM AIR HEATING SYSTEMS

Technical Reviewers & References

• Daniel Friedman - principal author/editor of the InspectAPedia ^TM Website
• Thanks to Mark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects" section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and home inspection educator.
• Thanks to Jon Bolton, an ASHI, FABI, and otherwise certified Florida home inspector who provided photos of failing Goodman gray flex duct in a hot attic.
• Thanks to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and for providing a copy of Carson Dunlop Weldon & Associates Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).

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.

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