Photograph of  this ugly duct routing risking water entry, mold, rodents, high operating cost.Duct System Defects
Heating and Cooling Duct Work Inspections for Adequacy, Safety, Defective Materials, Asbestos, Mold

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Defects in HVAC duct systems:

This article explains how to inspect and diagnose trouble with heating or cooling air flow, air ducts, air registers and zone components of heating and air conditioning (HVAC) duct systems.

This diagnostic article describes common defects found in HVAC duct work such as incomplete supply or return ducts, poor choice of location or size for supply and return registers, locating ducts in problem areas, leaks into and corrosion of duct work, leaky duct connections, and special notes on product failures by two manufacturers of flexible duct work.

The article includes important safety warnings about dangerous openings in HVAC duct work.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Diagnostic List of Heating & Cooling Air Duct Defects: Things to Inspect, Check, Repair, or Replace

We explain how to find and correct air duct problems 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.

Article Contents

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.

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.

Below we list some common sources of poor air flow from air conditioning or heating duct systems: check these first before ordering a more costly survey or repair job.

HVAC Supply & Return Air Duct Leaks & Obstructions - Theory vs Practice

Technical note: The D'Arcy-Weisbach equation for pressure and head loss can be used to calculate the actual pressure loss due to friction in a building piping or air duct system.

The D'Arcy-Weisbach formula

The Engineering Toolbox provides the D'Arcy-Weisbach formula:

Δp = λ (l / dh) (ρ v2 / 2)  


Δp = pressure loss (Pa, N/m2),

l = length of duct or pipe (m)

dh = hydraulic diameter (m)

ρ = density (kg/m3).

List of Common Air Flow Obstructions in HVAC Systems & Ductwork

Watch out: But keep in mind that even this apparently accurate calculation of the effect of piping on air pressure and airflow loss will not include the effects of obstructions in the building return air or supply air duct system such as


Continue reading at AIR FILTERS for HVAC SYSTEMS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Also see our explanation of problems with reduced air flow, dirty air handler blowers, blocked cooling coils, blower leaks and mold, frost and ice build up in ducts, and blower sizing problems of air conditioning retrofit projects which we discuss at: AIR HANDLER / BLOWER UNITS

Suggested citation for this web page

DUCT SYSTEM & DUCT DEFECTS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman