Flexible ducts or flex, as is generally known, is made from plastic that is wound over a metal wire coil to form a tubular structure. There are flex available in different configuration and this configuration differs from country to country. For example, while in Australia, glass wool and polyester fiber are used for achieving thermal insulation, in the US, only glass wool is used for this purpose.
Around the insulation of a flexible duct, there is generally a protective covering layer made of metalized PET or polyethylene. They are usually available in sizes of six inches to twelve inches long. These can be ideal for connecting supply air outlets to fixed ductwork. They are held in place by using metal band claps or long zip ties and are usually installed for shorter lengths. Some other interesting features related to them are also discussed here.
- It is important to provide support – If a flexible duct must work optimally, it is important to provide the needed support to it so that it can stay firm and in its place. A connection with equipment or a rigid duct can be regarded as a support joint. The provided support should be no longer than four feet apart with not more than half inches of sag per foot in between the supports. If there is a bend to a duct, then support must be provided before and after the bend. Support must be minimum of 1.5 inches in width. The straps should not constrict the air flow as it can lead to condensation. If it is a vertical installation, then it must be supported after every six feet so that there is proper air circulation through the duct.
- Ways to find out the needed flex duct – Just like a regular HVAC rigid duct, an appropriate flexible duct should be bought so that there is proper air flow through it. It helps in connecting the main duct area with an HVAC grille and without a proper duct the process will become more complex and will require more labor. To get the needed amount of flex duct for a place, find out the area of the place in square feet. Next, we need the CFM value. As an example, it can be useful to know that a well-ventilated home may need 1 CFM per square foot. Therefore, get the corresponding CFM value. After arriving at this value, one can easily consult an online duct calculator to find out the needed flex duct size. It may happen that the flex duct size arrived through this method may be different than the hard duct that is already installed but that should not be a cause of worry as metal fittings can help in fitting them properly to the rigid duct.
- It is important to clean the duct periodically – A flexible duct should be cleaned at a regular basis so that there is no buildup of dirt and air residue inside it. A clogged duct may not serve the whole purpose that it may be installed for. Hence, it is always important to keep it perfectly dry and clean. Cleaning the same is also easy and simple. If only a soft-bristled brush is used for the purpose that is enough. There are no special tools for cleaning a flexible duct. In extreme cases, though, if cleaning a duct may not be feasible or it is worn out beyond repair, it can be replaced.
A flexible duct can be made of aluminum as well as PVC plastic in some cases. Whereas a plastic duct may not last long, an aluminum duct can be more sturdy and useful. However, in certain applications, a plastic duct can be more suitable. Both types of ducts can be available in many types of variants and hence the cost of these types of ducts can vary significantly. They can be cheap as well as costly and selection can depend on the application, domestic or commercial.