HVAC Flex Duct Issues

Restricted Airflow

• The soft, flexible material of the flex duct allows it to bend into very tight turns and twists. However, the more the duct is bent or folded, the more restricted the airflow is, warns Inspectapedia. Many tight folds violate national and local building codes by significantly disrupting the airflow. When airflow is impeded, the furnace or air conditioner works harder to move the air through the home. Rooms stay cooler or warmer than is comfortable as well.

Easy to Damage

• The sheet metal used to create older duct work systems resists pest damage and won't rip if bumped. The soft insulation and foil that forms the sides of the flexible duct products tear easily and become damaged by rats and other animals commonly found in attics and between walls, claims Energy Vanguard. Accidentally handling this soft duct work the wrong way during installation can create a hard to see leak that lowers the efficiency of the entire heating and cooling system.

Long Ducts

• Difficult and cramped spaces in very small homes make installing even flexible duct work tricky. Sometimes contractors or homeowners use long runs of duct work to run the air around framing or through the walls where floor and ceiling access is not available. The longer the duct work runs, the more the air flow is reduced, according to Inspectapedia. Furnace and air conditioner blowers work best and wear out slower when the least length of duct work is used.

Clearance

• Flexible duct work needs to stay at least 4 inches above the ground to prevent water from soaking into the insulation wrapped around the core, says the American Society of Home Inspectors. When moisture soaks into it from a leak or a wet floor, mold and mildew grow inside the duct where it is hard to notice. Clearance to provide air flow between the duct walls and hot surfaces such as steam pipes is important, too.