January 2006

Ductwork Can Be Sneaky Energy Waster

More than one-third of your heating can be lost

For most of us, the ducts connected to our heating system are out of sight and out of mind. Most of us wouldn't know if our ductwork was leaking air we'd paid to heat. But rest assured your electricity bill knows.

“Leaking ductwork can waste up to one-third of the energy your heating system is producing,” says Cindy Haddon, WEMC marketing specialist.  “That means if it costs $100 to heat your home this month, you could have gotten by with only $66.”

Not only do leaky ducts waste energy; they can also adversely affect your family's health.

“If the return-side crawlspace ducts leak, mold, mildew, fungus and fumes from chemicals stored under your home could be sucked up and blown into the living space,” continues Haddon.

One out of two IS bad. These ducts are insulated but not sealed. Use mastic, a latex-based paste to seal sheet metal ductwork joints.

The situation has improved over the years with the advent of tighter energy codes. But even new homes can still have leaky ductwork.

So how do you tell if your ductwork is leaking?

• One room may be cooler that the rest of the house.
  
• You see separated joints or obvious holes in ducts.
  
• You see dirty spots or streaks in the insulation covering the ducts at ductwork joints.
  
• You feel air movement at ductwork joints (be careful of jagged sheet metal edges).
  
• You see old duct tape that has fallen away from joints.
  
• A certified contractor uses a blower door test or infrared camera that finds leaks.

Once you determine the ductwork needs to be re-sealed, there are two options. You can seal the ducts yourself or hire a certified contractor for the job.

• Use mastic to seal metal duct joints. Mastic is a latex-based paste that is smeared over the joint to stop airflow. Use a cotton glove that you don't mind discarding afterwards to apply mastic. Be careful of sharp sheet metal edges.
  
• You can also use duct tape–but not the cloth type that we're all familiar with.  Use a foil duct tape made especially for the job.  It should carry the UL label.

Not only should the ductwork joints be sealed; seal the transition between the indoor heating unit and duct system as well as any loose doors on the heating unit.   All sheet metal ducts should be covered with an R-6 foil-backed fiberglass insulation.

More Information: US Department of Energy

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