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• Heating & Air Conditioning Duct Routing & Support Guide
• Air Conditioning (or Heating) Duct Defects
• Duct installation defects, safety hazards

This chapter of "How to Inspect the Central Air Conditioning or Cooling System" describes proper (and improper) Heating & Air Conditioning Duct Routing & Support such as loose, sagging, crimped, bent or otherwise defective heating or cooling ductwork.

© 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.

DUCT ROUTING & SUPPORT - Errors & Guide

Air conditioning duct system defects include a remarkably wide range of errors, from failure to supply cool air or failure to even circulate air in the building, to health hazards such as use of asbestos material in or on duct work, to very dangerous conditions such as drawing heating equipment combustion gases into the building cooling (or heating) air.

This chapter describes errors to avoid when installing ductwork in buildings. Avoiding these errors will result in improved air flow, lower system operating cost, and may help in avoiding problems of mold or other contaminants in the heating or cooling duct system of a building.

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 and repairs.

Ducts in ground contact

When heating and cooling ducts are placed in ground contact, such as in the crawl space shown in the photo, not only is the contact going to conduct heat or cooling away from the duct before the air reaches its destination, but further, there is a significant risk of water leaks/condensation in the duct in damp or flooding areas (risking a mold or health concern) or rodent entry. Heating or cooling air ducts should be supported away from ground contact such as in crawl spaces.

Sharp Bends in Air Conditioning or Heating Duct Work Reduce Airflow

Sharp bends in ductwork restrict airflow (and violate ASHRAE or SMACNA guidelines for duct installations). Restrictions in airflow through duct systems increase the heating or cooling system operating cost and reduce the comfort of building occupants. This photograph shows flex-duct in an attic making a too-tight 180 degree turn, crimping and restricting airflow in the duct system.

Excessive or Unnecessary Duct Lengths Increase Cooling or Heating Cost

Excessive length of ducts is often found where flex-duct is installed by an amateur. If you see a length of flex-duct snaking across an area with multiple unnecessary twists and turns, the combination of length and unnecessary bends reduces airflow, with the costs just cited above. This photograph shows unnecessary lengths of small-diameter flex duct left by the installer. The small diameter of these ducts also tells us that we're looking at a high-velocity air conditioning system that uses a combination of small-diameter ducts and higher air velocity to deliver cooling air to the conditioned space. Flex duct runs should be as short and direct as possible without at the same time causing inappropriately sharp bends or kinks.

Pinched or Crimped Air Ducts Reduce Heating or Cooling Airflow

Other common duct routing errors include sharp bends in duct work, mismatched sizes of duct work among sections, flex duct which has become crimped or pinched to restrict air flow such as in the photo at left, and of course ducts which have become disconnected. We discuss and illustrate disconnected heating or air conditioning duct defects at DUCT CONNECTIONS.

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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.).

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