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Loose or Leaky Air Conditioning or Heating Ducts InspectAPedia®  -     Loose or disconnected air conditioning or heating ducts, causes, effects, repairs Air Conditioning (or Heating) Duct Defects

This chapter of "How to Inspect the Central Air Conditioning or Cooling System" describes the Effects of and How to Repair Loose or Leaky Air Conditioning or Heating Ducts, leaky air duct connections, defective heating or cooling ductwork.

The photo at page top shows what happens when cooling ducts are poorly connected through a crawl space. The crawl space was nice and cool but no cool air was being delivered to the living space. in addition, the air blowing around in the crawl space stirred up fiberglass and debris, including mold which increased the movement of these particles into the occupied space. Also see UNSAFE DUCT OPENINGS for other examples of duct leaks and openings.

© Copyright 2010 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.

This chapter continues discussion of common defects found in air conditioning duct work such as loose or leaky duct connections and their effect on the air conditioning or heating system.

DUCT CONNECTIONS - Poor duct work connections

Most-common Types of Air Duct Leaks

A client who lived in an apartment in New York City engaged our company to find why her city apartment could not get cool even though she had a new air conditioning system installed. We found that the ducts had become disconnected in the attic crawl space where the air handler was placed. It was wonderfully cool in the attic. The apartment was quite hot.

These photographs show the two most-common air conditioning or heating duct leaks, at a loose falling metal duct connection (left photo) and at a poorly-secured flex-duct connection (right photo). Leaking supply air at these connections means less cool air (or warm if it's heat) delivered to the occupied space.

If the air conditioning system output at the registers is poor, especially if it is working in some building areas but not others, one of the first things to check is the condition of the duct work. Look for and seal leaks like these. Also review the other duct and supply adequacy defects described at articles linked-to from the left of these pages.

The cure for these duct leaks is simple: reconnect leaky duct sections. We use metal foil tape to complete the seal on connected metal duct sections. The flex-duct connection was re-made and a tighter plastic band used to secure the flex duct in place.

Duct Retrofit Leaks in Old Buildings

These photographs show what can happen when existing registers and in-wall ducts are re-used when installing updated air conditioning or heating ducts in a building. The photo with my hand shows us feeling an up-draft from the basement below this first floor bath even though the air conditioning system was not running. The second photograph shows the problem as seen from the basement.

The duct installer had simply pushed smaller-diameter new oval ducts up into the existing duct riser from the basement, leaving more than an inch of opening between the old rising duct and the new inserted duct. The result was leakage of cool air backwards into the basement when the central air conditioning system was running, and leakage of (moldy, smelly) basement air up into the living space through the same opening (by convection) when the air conditioning system was off.

The cure for this duct leak was to use some spray foam insulation to make a better seal at the basement ceiling as well as around the register in upper floor.

Rooftop Duct System Leaks & Water, Mold, and Pathogens

These photographs show what happens when a rooftop packaged-terminal air-conditioning airhandler
(PTAC) and horizontal runs of air-ducts are installed on a roof surface and when that air duct system is improperly sealed and also is lined with fiberglass insulation.

Water ponded on the old, concave sections of air conditioning ducts on the roof of this commercial office space. As water leaked into the duct system it saturated fiberglass duct liner which in turn, had its normal coating of organic dust and debris from the building, risking an indoor mold or pathogen problem for some of the occupants.

The cure for these duct leaks was costly: it was determined that it was less costly to completely replace the rooftop ducts with new metal ducts using outside insulation than it would have been to remove the contaminated fiberglass liner, clean the existing ducts, repair the leaks, and insulate their exterior. The work was combined with other building HVAC cleaning and repairs.

Return Duct Air Leaks & What They Mean

When the air conditioning or heating system is in operation, return ducts are under negative pressure (since the blower in the air handler is drawing air in to the cooling or heating unit). This means that:

• The system is drawing return air from spaces other than the conditioned space
• The air conditioning or heating system operating costs are increased
• There is the potential for drawing un-wanted dust, mold, pathogens, or even combustion gases or flue gases into the system and therefore moving these into the living space

Also see UNSAFE OPENINGS

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Technical Reviewers & References

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• Additional technical contributors & reference sources for this article are listed below.

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

• 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.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
• Complete List of Air Conditioning & Heat Pump Design, Inspection, Repair Books at the InspectAPedia Bookstore.
• Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
• Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
• "Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
• Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
• Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) 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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