Most consumers know spring and fall tune-ups make your system more efficient, but you should also check your duct work if you have a forced air system.  If you have central air conditioning, you probably have a forced air system.  The three main elements to proper duct maintenance are physical repairs, sealing and cleaning.  

Physical repairs

The most important consideration is the physical condition of the duct work.  Ducts should be:

• securely attached to their support structures,
• with no holes or gaps where different sections connect, and
• with no leaking of water or other fluids onto or into the ducts.  

Some repairs can be done by the homeowner, such as reattaching a sagging duct section or insulating a cold water pipe that drips condensation during high humidity conditions. More extensive work is best done by the professionals.

Sealing

Duct sealing is also important to the overall efficiency of your HVAC system. A very efficient system becomes far less efficient if the duct work is not properly sealed.

Some of the conditioned air is wasted if it leaks out as it travels through the ducts, forcing the equipment to work harder to provide cooler air to the living spaces. This is particularly true if the duct work passes through an unconditioned area, such as a crawl space or garage. Sealing and insulating the ducts reduce this waste.

Some leaks may require significant physical repairs, while others can simply be sealed using duct mastic, a sticky mixture that makes an airtight seam. Or seal your ducts with duct tape that is approved for HVAC work and is listed with the Underwriters Laboratory (UL) standard.  Do NOT use household “duct” tape.

Look for small leaks at seams where duct sections come together or where screws have been put into the ducts to secure them. This job is fairly easy in areas where the duct work is exposed, but may be more difficult or economically prohibitive in areas where the ducts are behind finished walls, floors or ceilings.

Again, minor sealing can be done by the homeowner, but extensive work is best accomplished by the professionals. Every leaking seam or hole that is sealed will improve your system’s overall efficiency.

Cleaning

Regular duct cleaning is not likely to result in higher efficiency of your HVAC system, but it will improve your indoor air quality. The U.S. Environmental Protection Agency (EPA) provides useful information in its document, Should You Have the Air Ducts in Your Home Cleaned? In particular, the EPA recommends that you consider having your air ducts cleaned if you notice any of the following problems:

• substantial mold growth inside ducts, hard surfaces (e.g., sheet metal) or other components of your HVAC system. A laboratory test may be required to determine whether a substance is indeed mold.  
• ducts infested with rodents or insects.
• ducts clogged with excessive amounts of dust and debris, and/or particles actually released into the home from supply registers.

If any of the conditions identified above exists, additional repairs may be necessary to prevent the problem from returning.

Before deciding whether or not to have your duct work cleaned professionally, review the full EPA publication at www.epa.gov/iaq/pubs/airduct.html.