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AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of HEATING & COOLING TERMS
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
FAN NOISES, HVAC
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
Loose or leaky air duct troubleshooting: this article describes the effects of and how to find & repair blocked, clogged, crimped, 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.
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For diagnosing poor air flow from an air conditioning or heating system also see RETURN AIR REGISTERS & DUCTS and SUPPLY DUCTS & REGISTERS. We also provide a checklist of more air duct troubleshooting suggestions at RETURN DUCT AIR LEAKS or at SUPPLY DUCT AIR LEAKS. And at UNSAFE DUCT OPENINGS we discuss certain air duct leaks and openings that are downright dangerous.
This article 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. Our air duct photos above illustrate common air duct leak problems that not only go unnoticed or undiscovered but that increase heating or cooling costs by leaking supply air.(SUPPLY DUCT AIR LEAKS) Similar leaks in return air ducts can pick up and distribute contaminants in a building (RETURN DUCT AIR 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. So were the electric bills. Below at Soffit Cool Air Blast we describe a more egregious case of duct work that was missing entirely.
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 (photo at left).
In addition to making a mechanically sound connection between duct sections (sheet metal screws, mechanical fasteners, nylon tie strips), 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.
Watch out: don't rely just on duct tape to secure air ducts.
But the cost of air duct leaks can be significant if the leak persists over a long time or in a location where blowing air or loss of dehumidification lead to mold or other indoor air quality concerns. Leaky air ducts can significantly increase building heating or cooling costs and can lead to other building or even health worries. The Florida air duct leak field report case just below illustrates this problem.
From a different building, here are photos (below left) of an air handler drawing all of its return air from a basement and another building in which supplemental return air was being taken from the crawl space.
These are examples of a "one way" heating or air conditioning duct design - all HVAC air originates in the basement and is "conditioned" before being blown into the building. This is the most costly and least healthy duct design. At Return Duct Air Leaks & What They Mean we summarize the impact of missing or open return air ducts.
The photographs above as well as the rusted HVAC return duct system at left 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 or when no one has inspected the condition of the HVAC duct system for decades.
The photo with my hand (above left) 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 (above right) 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.
A cure for the first two duct leaks shown above 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.
The photo at above left showing a rusted-out floor return duct system illustrates a common problem on older homes: rusted sheet metal that ultimately perforates. This interesting return air system also enjoyed picking up both crawl space air and, depending on wind direction, nice cold outdoor air from the crawl space vent visible in the lower portion of our photograph.
To correct the rusted-out return duct system that was using the space between floor joists as ductwork (common in older homes in North America) required removal and reconstruction of the return duct system.
The photos above illustrates leaks into a rooftop packaged-terminal air-conditioning air handler
Details are at ROOFTOP HVAC UNITS
In addition to correcting obviously gross HVAC duct leaks such as missing ducts or damaged/disconnected ductwork, leaks at HVAC duct connections should also be sealed against leaks out (supply ducts) or leaks into the ductwork (return ducts). Both types of duct leaks increase building energy costs to heat or cool the structure and in the case of return duct leaks, health and environmental contaminants can also be introduced into the HVAC system by such leaks.
Authority for actually requiring that HVAC duct connections be sealed comes from model energy codes, building codes, and state or provincial adopted versions of those building code guidelines.
For example, the Residential Code of New York State requires that all HVAC ducts be sealed. We interpret this to mean all duct joints and any other leaks that might be observed along the run of HVAC duct work such as where flexible metal ductwork elbows or tees are installed or where flex-duct may have become damaged.
Home inspection associations point out in publications and training materials that while HVAC installers may comply with the intent of the model building or energy codes, we often observe that compliance only at recent or new duct installations. According to the Central New York ASHI Home Inspectors Association, quoting
Code citation example for duct sealing requirement: NYS RM1601.3.1 Joints and Seams
- Special thanks to ASHI Member Greg Harwood [Dec], CNY ASHI Observer, May 2006, re-published by that association in 2012.
More detailed suggestions of things to check in the duct system to improve airflow are at RETURN DUCT AIR LEAKS or at SUPPLY DUCT AIR LEAKS. Also see UNSAFE OPENINGS or select a topic from the More Reading links shown below.
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