All About Heating and Air Conditioning Ducts

Izmirian Sheet Metal Work - Duct works

We are often asked about repair, replacement, or installation of new ducts in homes and businesses.  Heating and cooling systems often suffer 30-40% air leakage or loss through thermal conduction in poorly sealed or insulated ducts.  Comfort or balance issues also arise from poorly designed, poorly installed, or crushed ducts.  Duct repair or replacement can be one of the most effective and cost beneficial investments in energy efficiency and comfort in your home.

Ductwork evaluation starts by reviewing comfort issues in the occupied space with the homeowner.  Are there hot spots, cold spots, draftiness, noise, odors?  Do the occupants complain of dryness or excessive moisture?  Excessive heating and cooling bills?  These conditions can often be related to ductwork issues.

A visual inspection of ducts is usually all that is needed to discover if action is necessary:

  • If the ductwork is covered with a readily identifiable asbestos containing material, the owner may choose to abate and replace.  There is no requirement to abate asbestos containing ductwork, but it is often prudent if the material is highly friable (falling apart) or subject to disturbance.  Asbestos containing duct wrap has no thermal value, so if the duct is not replaced, it should be overwrapped with fiberglass insulation.
  • Dark staining on fiberglass insulation is indicative of duct leakage.  This is easily repairable by stripping off the stained insulation, sealing the duct or fitting with a latex based sealing compound, and re-insulating the ductwork.
  • Broken joints and crushed ducts are usually the result of workers accessing the crawl space.  Whenever possible, we make the repair in a way that allows better access through the crawl space.
  • Insulation is often thin and compressed, leaving very little insulating value.  Existing insulation can be overwrapped with new fiberglass insulation to reduce conducted and radiant heat loss through the duct.
  • Ductwork that is poorly designed, poorly installed, badly deteriorated, or exposed to rodents should be replaced.

Ducts can also be tested with equipment designed to determine the amount of duct leakage present.  It does not locate where the leakage is occurring, but does indicate if a problem exists.  This can be useful if the ductwork is inaccessible or if an objective measure of leakage is necessary.  We are happy to refer you to a testing company certified to measure duct leakage.  California requires that this type of testing occur with any equipment installation in the State’s more severe climate zones.  It is not required in the San Francisco bay area.

Types of Duct Materials

  • Galvanized steel round pipe
  • Galvanized steel rectangular duct
  • Aluminum flex duct
  • Wire flex duct
  • Ductboard
  • Insulation
  • Vapor barriers