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Using A Fog Machine To Test For Duct Leaks

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When looking for ways to reduce energy usage, many homeowners forget to check the air ducts connected to their HVAC systems. However, leaky air ducts can be responsible for up to 25 percent of energy loss in your home. While it's best to have an HVAC repair company test your air ducts for leaks, you can also do this yourself in a couple of different ways. One way is to use a fog machine. Here are step-by-step instructions on how to do it.

Why Use a Fog Machine

Fogging machines—the kind used to create a smoky effect at parties and in movies—can aid in identifying whether or not you have leaky air ducts by providing a dramatic visual marker. Smoke streaming out of the ducts not only confirms there are leaks but may also help pinpoint where patches need to be made.

Be aware, though, that this procedure takes several hours and requires you to be able to check the duct work throughout your home, which may mean crawling in small spaces or walking through your attic.

Equipment Needed

For this test, you'll need:

  • Duct blaster fan with flexible extension duct
  • Fog machine
  • A piece of heavy canvas or drop cloth
  • Vent tape, masking tape or duct mask
  • A smoke pencil

You can rent or buy a duct blaster fan from a home improvement store or equipment rental company. The fog machine can be obtained from any party store. Just don't forget to also get the liquid solution that makes the fog.

How to Fog for Leaks

The first step is to cover all the registers in the home, both supply and return,  with vent tape, except for the central return register. It's not enough to simply close them as the fog can still escape and negatively impact your results. The vents should be covered as much as possible.

Next, connect the duct blaster to the central return register by first taping the square transition piece from the flexible extension duct to the center of the vent. Once that piece is secured, tape off the rest of the opening on the register and then place the end of extension duct to the collar of the transition piece and secure in place using the accompanying strap.

Go around your home and turn off all exhaust fans, air conditioners, dryers and anything else that uses or circulates air in the home. However, you will want to open one window to stabilize air pressure in the house while the duct blaster is running. Be certain to also set the controls on the temperature panel so that the fan on your HVAC system does not turn on during the test.

The next step is to connect the speed controller to the duct fan and plug the system into an electrical socket. When you've completed the preparations, turn on the duct blaster and wait a few minutes for the fan to pressurize the ducts. Turn on the fog machine and place it in front of the duct blaster. Cover the two machines with a drop cloth or heavy canvas to prevent the smoke from escaping into the home. Now inspect your ducts.

Any area where smoke from the fog machine is present means there's a leak. You can further confirm this by using the smoke pencil. Turn off the duct blaster and fog machine and wait until the smoke clears. Walk around holding up the smoke pencil to the seams and joints of the ducts. Inspect areas that cause the smoke to blow around for holes and rips.

You can patch up holes and leaks using a variety of duct sealants. For information about repairing leaky ducts or to have a professional do it for you, contact  HVAC services in your area.


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