The most common types ducts that can be used for a bathroom exhaust fan installation are rigid ducting, semi-rigid ducting, flexible ducting or a rigid duct and flexible duct combination.
Found the answer to this after I called the inspector on our job. As of 2020, you can use aluminum flex duct to vent a bathroom fan as long as the total run is less than 25 feet.
Rigid is best but for bath exhaust flex metal is OK. Vent to outside, ideal is straight up through the roof (every bend introduces resistance and reduces efficiency) but if you have to go out via the soffit, it's better than no vent at all.
Disadvantages of Flex Duct
Flexible ducts are more prone to air leakage around the seams, which can lead to lower HVAC system performance. Additionally, the pliable nature of flex duct tends to make them prone to tangling or crushing when they pass through tight spaces or fixtures.
New NEC® Section 422.18(B) states that metal parts of ceiling-suspended (paddle) fans in bathrooms and shower spaces shall not be located within a zone measured 3 feet horizontally and 8 feet vertically from the top of the bathtub rim or shower stall threshold.
For example, flexi duct can be used for a bathroom fan's system, but is prohibited in dryer ventilation systems, and PVC and PVC coated aluminum can be used for bathroom fan ducts, but is very dangerous to use for dryers.
The longevity of HVAC flex ductwork hinges on several key factors, including material quality, installation, and maintenance. Typically, well-installed and properly maintained flex ductwork can endure for 15 to 25 years.
Rigid metal ducts offer lower airflow resistance, which means less wasted energy. With more efficiency, you can reduce your power bill while saving money in the long run.
Can you use flexible ducts for HVAC systems? Yes, but you should consider more than just the benefits before installing them. As versatile as flexible ducts are, they come with certain drawbacks that you need to be aware of before making a final decision.
That's why it's fine to have bathroom vents in a basement or lower floors to leave through the side of the home. To help your attic stay clear of mold or mildew, make sure all exhaust fans running through the attic leave through the roof. For one, you'll lessen the chance of the warm air getting back into the attic.
A fan that is too big can cause a bathroom to be cold and noisy. This is why calculating the correct CFM is important.
The most common option for bathroom exhaust fan venting is the ceiling to wall venting option. The second most common is the roof vent installation. The third most common is probably the vertical wall installation.
The length of a “flexible air connector” is limited to 14 feet maximum. The length of a “flexible air duct” is not limited in length.
After decades of proving its worth as a component in underground fuel-delivery systems, flex pipe is rapidly becoming a first-choice option for vent-pipe applications, and the current fiberglass crunch is another reason that makes flexible vent pipe a reliable alternative to rigid or semi-rigid fiberglass pipe.
❖ The length of flexible air ducts is not limited, unlike flexible air connectors, which are limited to 14 feet (4267 mm) (see commentary, Section 603.6. 2.1).
Don't let the ducts sag more than ½ inch per foot between supports; maximum sag shouldn't exceed 2½ inches. Support straps should not compress the inner core or constrict airflow.
An HVAC system needs ductwork and one type of ductwork used is called a flex duct, which is short for flexible duct. It moves air from the HVAC system to different areas of a building. Flex ducts are made of plastic. They are known for being very adaptable and easy to install.
Over time, dust and debris can build up in the ducts, affecting the efficiency of your system. While you may be familiar with cleaning rigid ducts, you may wonder if flexible air ducts can be cleaned. The answer is yes, but to avoid damaging the ducts, you should hire a pro to clean them.
Flexible, non-insulated ducts cost $1 to $3 per linear foot; insulated ones cost $2 to $4 per linear foot. Fiberglass ducts range from $4 to $6 per linear foot, while sheet metal is the most expensive at $7 to $13 per linear foot.
However, the IAPMO passed a ruling stating that flexible piping should be no longer than five feet for residential properties. After review, it was extended to six feet, but it could still cause issues with a project if you can't use flexible ducts.
Yes, Flex ducts are a perfectly valid option to use a conduit for your bathroom exhaust fan.
Use Solid Ducting Wherever You Can
The smooth sides of solid ducting provide a huge increase in performance: Smooth sides allow the air to travel through the ducting without being impeded by 'ribs' and 'imperfections' associated with flexible duct.
For better performance, duct runs should be as straight as possible. If a bend is necessary, 2 to 3 feet of straight duct should be allowed to run from the fan exhaust port to the first elbow in the duct run.