How to Fix Duct Work Under a House

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Things You'll Need

  • Hand-held mirror

  • Bright light

  • Foil duct tape

  • Utility knife

  • Duct support straps

  • Nylon pull ties

  • Sheet metal screws that are self-taping

  • Screwdriver

Duct work must be clean and leak-free for proper operation. Insulated duct work keeps the cool air cool and the hot air hot inside the duct work. The goal is to keep the air inside the duct work isolated from outside air and pollution-free from the source to the output vents. This improves the efficiency of the heating and cooling system and adds to your comfort. A proper inspection of the existing duct work will determine how to make the repairs.


How to Fix Duct Work Under a House

Step 1

Determine how dirty the duct is by looking inside. Locate a straight piece of duct that can be accessed from both ends. Place a bright light in the duct work at one end. Go to the other end, and use a mirror to look inside the duct. Place the mirror so the reflection reveals the duct's condition in the direction of the light. Use several different locations for the light and mirror until you have inspected the entire duct system. The amount of dust or pollution determines if it needs to be cleaned or replaced. You can hire contractors to clean the system using compressed air hoses and a powerful vacuum to blow and pull the dust out.


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Step 2

Locate any leaks that are in the duct work by feeling for air escaping from any direction around the ducts. Usually the connecting joints are the problem areas. Pull the insulation back to locate the exact location of the leak. Improperly supported ducts can sag and open up a leak. Metal ducts, fiber board and flexible insulated hose ducts are commonly found. Some systems contain all three types.


Step 3

Push the pieces back together, and use self-taping sheet metal screws to attach the metal duct pieces together. Sheet metal ducts must have insulation covering them. Cover the complete duct with insulation, and use tape to secure it in place.

Step 4

Use screws and foil tape to hold the fiber board duct pieces together. Add support straps or nylon ties to support the duct.


Step 5

For flexible insulated hose ducts, use nylon ties and foil tape to hold the pieces together. Stretch the inner flexible hose over the metal connection, and tape it securely. Support the duct on support straps or nylon ties attached to the house.

Step 6

Test for leaks after the repairs are made. Make sure the ducts are airtight with no leaks. Add enough support straps to counteract the effects of gravity. Support the duct in straight and level line to avoid future sagging or pressure at joints and connections.


Place plastic sheeting on the ground for a clean place to lay down if there is not much room in your crawl space.

Keeping your filters clean prevents large amounts of dust from accumulating in your duct work.

Attach support straps to the house at secure locations such as floor joist or beams, not the subfloor itself.


Always take safety precautions and wear proper safety equipment while operating machinery or using hand tools.


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