Manufactured or mobile homes often contain poorly sealed heating, ventilation and cooling ductwork, so it is essential to understand where leaks are apt to occur and what you can do to seal them. It isn't difficult or expensive to seal ductwork leaks, and most homeowners can perform the job in a few hours of work. Below is what you should know about likely leak points and how to effectively and permanently reduce your energy costs by sealing these vulnerable locations:

Understanding where leaks are probable

Most manufactured homes contain one or more lengthwise ducts that run along the bottom of the home. These ducts are connected to the furnace or air handler, and the ducts contain multiple openings where heated or cooled air can enter the home. All of the ductwork should be concealed and protected by a polyethylene underbelly, which is a material similar to that used in tarps.

Within the ductwork itself, there are several areas where leaks are prone to occur. In almost all situations, the leaks originate in the joints between two sections of the ductwork. Below are the most common components that are prone to leakage:

  • Termination cap - These galvanized metal caps serve as ends to the main ducts.

  • Boot - Most mobile home ductwork contains several boots, which are short vertical risers that distribute air into the home via openings covered by vent grilles.

  • Plenum - The plenum is the bottom portion of the furnace or air handler that connects to a boot.

  • Branch duct - A branch duct is a smaller duct that runs perpendicular to the main ducts; this distributes air across the bottom of the home to areas on the opposite side of the main duct.

At each junction, such as the main duct with the boot, the gaps must be sealed before you can find the best efficiency; otherwise, you can expect to lose a considerable amount of cooled or heated air.

How you can seal the joints between duct components using mastic

Sealing the leaks using mastic is straightforward and simple. Mastic is a compound consisting of a binder material integrated with fiberglass strands; it maintains flexibility as it cures. While aluminum tape is often used to seal ductwork, it can fail over time and lose its ability to adhere to the ductwork. Mastic, however, is designed to be a permanent solution. Here is how to apply it:

1. Access the ductwork beneath the manufactured home - To gain access to the ductwork, you will need to cut a slit in the underbelly. However, before cutting a full length slit, you should also be sure you are in the right place by feeling around on the underbelly for the ductwork that lies just above. This will help lead you to the general areas where you should cut. Once you are comfortable with the location to cut, use a utility knife to carefully cut open the underbelly material; cut slowly and deliberately, and don't make the slit longer than necessary.

2. Choose and clean the location for applying mastic - Once you have access to the underside of the manufactured home, locate joints between the various duct components mentioned above. Next, dampen a rag in rubbing alcohol and wipe down the duct joints and surrounding area to remove grease or other contaminants. Allow the alcohol to evaporate before moving to step 3.

3. Apply the mastic - After cleaning the joint locations, put on a pair of rubber gloves and dip your fingertips into the mastic container. Take a small wad of mastic and smear it onto the top of the joints, being sure that it is pushed into any gaps or spaces. Move all around the joint and apply mastic generously; be careful not to make your mastic layer too thin. Once you have finished sealing the joint, move on to the next joint. After all the joints have been sealed, allow the mastic to cure as directed by the manufacturer of the product.

4. Reseal the underbelly - The last step is to repair the slit you cut into the underbelly. To seal the underbelly, cut a piece of polyethylene material in the same size and shape as the slit, allowing 2 to 3 inches on each side of the damage. Finally, attach the patch to the underbelly using polyethylene-approved tape.

For help with this project or if your system still isn't working efficiently, contact a local heater repair company.