Water that leaks into the air duct and stays there causes mold to breed. While the EPA does not recommend frequent cleaning of air ducts, a water leak is an exception because it poses health risks when the mold is carried into your house every time you run the furnace. Depending on the severity and frequency of the water leak, you can make use of the following to manage or keep the water from your air duct:
Sponges or Rags
You can take a long pole such as that of a mop or broom and tie rags or sponges to one end. Push the pole into the air duct and allow the rags or sponges to absorb the water. This is ideal if the water is not pooling and can easily be cleaned by the rags.
This method involves lowering the hose of a wet-and-dry vacuum into the opening of your air duct towards where water has gathered, and sucking it all out. Occasional water leaks that happen only when there is heavy rain or melting snow can be remedied by this method. For larger jobs, you can rent the industrial-sized vacuum cleaners for a more powerful suction.
Canals or Ditches
For a more persistent water leak problem in the air duct, you can dig a canal or ditch around the house and towards the lowest point of your property, making sure the bottom is parallel to the said lowest point. This is where the water is supposed to exit. The idea is to direct the water flowing under the top soil into the canal instead of having it leak into your air duct. You can fill the canal with gravel so water can move easily and can even cover the top with sod to conceal it from the rest of your lawn. At the exit point of the canal, insert a pipe with holes. This solution is good for frequent water leaks into the air ducts that are built under the concrete slab of the house. This is also applicable as long as the duct work is still in good condition.
Moving to the Attic
When digging a ditch around your house is not feasible or when your duct work has deteriorated beyond repair such as when it is broken, crushed, heavily rusted or any other structural-related damage: consider abandoning the air duct under the slab altogether and building a new one overhead through your attic. This option consists of filling in your old duct and planning for the new duct work. This might require you to expend more money as compared to the previous options but can save you from future water leak headaches.
Note, however, that when taking this option, the duct work in the attic also has its own water-related problems such as condensation on the ducts. It is best that you take into account proper ventilation and insulation so moisture that eventually results to mold problems will be prevented.
Contact an HVAC Professional
When all else fails or when you are unsure of what is causing the presence of water in your air ducts, consider contacting a reputable HVAC professional. A good HVAC professional is trained to assess the problem and recommend the solution for you to implement.