Duct Sealing

If your home relies on ductwork to distribute conditioned (heated or cooled) air, duct sealing is one of the most effective and inexpensive projects to improve your home’s comfort and efficiency. In an average home, leaky ducts can waste hundreds of dollars in heating and cooling each year.

energy efficiency duct sealingIf the duct leakage is 20% of the total airflow, the efficiency of a cooling system can drop by 50%. Heating efficiency is similarly affected. Duct leakage also lowers heating and cooling capacity, and can shorten equipment life.

While the increase in energy costs is significant, protecting health and safety is of equal importance. Ducts are usually located in the attic, crawl space or basement. If the return ducts leak, they draw air from these areas directly into the home. This air can be contaminated with dust, mold, excess humidity, and potential toxins like radon, and pesticides. If the leaks are bad enough, they create lower pressure inside the living space, further drawing in contaminants.

If you use gas to heat water, cook your food, dry your clothes, or heat your house, you should know that these appliances release gases such as carbon monoxide in small quantities through their ventilation systems. Leaky ductwork in your heating and cooling system may cause “backdrafting,” where these gases are drawn back into the living space, rather than expelled to the outdoors. So there’s a safety issue to consider, as well as one of energy efficiency. Sealing ductwork minimizes air quality issues, and we also recommend that all houses have a carbon monoxide detector along with the smoke detector.

Ductwork is often neglected simply because it’s largely hidden away behind walls or between floors, out of sight and out of mind. Older homes are more likely to have serious leaks, due to both age and to the fact that less attention was given to efficiency and the important role of ductwork in years past.

Take a Look at Your Ducts

Regardless of your home’s age, it’s worthwhile to periodically inspect accessible ductwork found in basements or crawlspaces, attics, garages, and utility closets. You can do this yourself in most cases, or turn to an expert contractor.  Start with a visual inspection of the system. Energy codes require that all joints in the ductwork be sealed.  However, many leaks are not readily visible; you must pressure-test the ducts to determine if they are leaking. After temporarily taping over the registers to create a supposedly sealed system, you or a subcontractor can use a special fan to blow air into the ducts to determine the amount and location of leakage. The test takes about an hour.  Some contractors conduct the test for a nominal fee or include it as part of a bid to seal leaky ductwork.

Examine your ductwork for:

  • Holes or tears.
  • Disconnected ducts.
  • Kinks or crush damage.
  • Cracked or worn seals at HVAC equipment and filter slots.
  • Connections at registers and grilles.
  • Excessive dust, moisture, or other debris in ducts.
  • Dirt streaks in insulation around ducts.

How to Seal Your Ducts

To seal ducts yourself, you’ll want to use mastic sealant or metal tape—duct tape, despite its catchy name, doesn’t last very long and shouldn’t be used. Damaged sections that can’t be repaired with sealant or tape will need to be replaced.

You’ll want to fix the most important ducts first. Here’s a roadmap to help you make a plan:

High Priority Leaks

  • Disconnected components.
  • Connections between the air handling unit and the plenums  (a plenum is a separate space provided for air circulation for heating, ventilation, and air-conditioning).
  • All seams, especially in hard-to-reach places.

Moderate Priority Leaks

  • Joints between sections of branch ductwork.

Lower Priority Leaks

  • Longitudinal seams in round metal ductwork.

Insulating ducts will further improve efficiency and inhibit minor leaks; pre-formed foam insulation, available at most home improvement stores, is easy to install. Ducts in unheated areas, such as attics, will especially benefit from insulation.duct-insulation

There are some situations when do-it-yourself duct sealing won’t be enough. If you suspect inaccessible ductwork is also leaky or damaged, have a technician come out to inspect the whole system. And if you discover a large amount of foreign debris in your ducts—anything more than a thin coating of dust—you will probably want to have it professionally inspected and cleaned. Large amounts of mold or evidence of pests may require special removal efforts.

Once you’ve got your ducts sealed, and perhaps insulated, maintenance is easy– just continue inspect ducts once or twice per year to make sure no new leaks have developed.

Behind the Walls
Innovation Center
One Broadway
Cambridge, MA 02142