With its smooth inner walls, rigid metal ducting reduces friction making it the most effective choice for a bathroom fan duct. Rigid ducts are low maintenance. They have a long lifespan.
Semi-Rigid Aluminum Duct is ideal for bathroom fan exhausting. This new patented duct combines strength and flexibility for easy and safe installation.
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.
Rigid ducting should be used wherever possible in a ventilation system, so to minimise duct resistance and bends in the system.
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.
Sheet metal ducts are considered the most energy-efficient material because of their exceptional durability and enhanced airflow. However, they can also leak air at the duct joints and seams. Galvanized steel is a great duct material because it is durable and non-porous.
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.
Exhaust fans should always be ducted to a location outside the home (See Kitchen Exhaust Fans and Bathroom Exhaust Fans). Ideally, each exhaust fan should have its own individual duct to the outside and each unit should have its own ducting to prevent cross contamination.
Ridge Vents: What You Need to Know
They are considered one of the most effective types of roof vents due to their design and positioning. Ridge vents work by creating a continuous air channel, allowing hot air to escape and fresh air to enter through intake vents located at the lower parts of the roof.
The most popular venting option for a bathroom exhaust fan is a pipe extending vertically through the roof. This choice only works on home designs that allow a straight vertical pipe with no bends. It's the most efficient means of pulling moisture out with the least chance of moisture re-entering the home.
The fan should be ducted to exhaust outside of the home, not into the attic, crawlspace, garage, interstitial floor space, or wall cavities. Operable windows should not be relied on for consistent bathroom ventilation.
Codes have changed over the years and where 3” duct might have been common, it is now 4” duct. Many codes and builders across the USA are even going up to 6” duct as standard.
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.
Code Requirements for Bathroom Exhaust Fans
Chapter 15 of the International Residential Code (IRC) requires bathrooms and toilet rooms to have a minimum local exhaust capacity of 50 cfm intermittent or 20 cfm continuous.
Yes, Flex ducts are a perfectly valid option to use a conduit for your bathroom exhaust fan. The manipulatable nature of flexible ducts allows them to fit into environments in which the connection to the outside is not a straight line.
This can cause warped cabinetry, foggy mirrors, and mould or mildew growth. A fan that is too big can cause a bathroom to be cold and noisy. This is why calculating the correct CFM is important.
To adjust the CFM, you can change the speed of the blower or alter the ductwork size. Increasing the blower speed won't have much effect if a room's duct is too narrow. A 12' x 12' foot room is 144 square feet. You generally need at least 1 CFM per square foot, meaning that room's duct should have a 144 CFM capacity.
On the other hand, if your CFM is too high for your room size, it can cause ventilation problems. Too much air results in too little ventilation, which in turn causes high humidity. The excess moisture in the air can then lead to mold and mildew, as well as other problems.
Cubic feet per minute: Calculating the CFM involves taking the HVAC unit's size in tons and multiplying it by 400. Next, divide that total by your home's square footage. That result gives you the CFM, which is used with the following factors to get the HVAC duct size you need.
Rigid ducts are made from galvanized steel or aluminum. They can be either rectangular or cylindrical in shape. Rigid ducts are more durable than flexible ducts and can withstand extreme temperatures.
Understanding the three types of ducting – flexible, rigid, and semi-rigid – is essential when selecting the appropriate ducting for your residential HVAC system. Factors such as space requirements, system pressure, indoor air quality, energy efficiency, and maintenance should guide your decision-making process.