No. Avoid flexible duct for your range hood, regardless of the CFM. Flexible duct is a poor investment because it is: Not durable/sturdy.
Rigid duct is without a doubt the best option for venting your range hood. Rigid duct is higher quality than flex duct and is made of much more durable materials. For more information on choosing the right type of duct for your range hood, check out this article.
Metal duct can still be found in many older homes, but flexible duct is more prevalent in newer homes. Both work well. Still, should you decide to change from metal to flexible duct, don't waste money on an HVAC contractor. It's a time-consuming job, but definitely one you can do yourself.
It doesn't last as long as metal ductwork, it is thin and can puncture easily, and it doesn't hold up to normal wear and tear as metal does. Over time, flexible ducts can become brittle and break or crack with even a slight touch.
You can insulate your vent hood duct, but it's not required. Insulating your vent hood duct will keep the noise down and keep your greasy kitchen air from escaping into your joists and attic.
Can flexible duct be used for a range hood? No. Avoid flexible duct for your range hood, regardless of the CFM.
Many microwave ovens are not vented to the outside. If you are willing to give up the outside venting feature, you can have a service person from the appliance dealer turn the fan around to vent inside. Remove the wall jack and insulate and seal the wall opening.
If you've ever seen kinked or sagging flex duct and wondered whether that was a problem, you were onto something! Since flex duct, by definition, is flexible, it often flexes in ways we don't want it to. The result is poor airflow and ineffective HVAC systems.
The listing label on “flexible duct” is rectangular in shape and states “Listed Air Duct.” The listing label on a flexible air connector is circular in shape and states “Listed Air Connector.” Both are listed to UL 181 requirements. The length of a “flexible air connector” is limited to 14 feet maximum.
Flex duct is widely used for return air in commercial air conditioning systems. Flex duct is able to withstand a certain negative pressure of return air. When installed properly, a flex duct is a reliable and convenient ductwork solution. Flex duct often gets a bad rep because of airflow issues.
Flex ducts are better for existing trunk-and-branch heating and cooling systems. This is because they're more versatile and flexible. Metal ducts are more rigid due to the nature of steel, making them ideal to build an entire HVAC system.
Flexible air connectors which are listed to UL 181 are allowed by the standard in lengths up to 14 feet. This product is specifically evaluated for the maximum length up to 14 feet, and the manufacturer's installation instructions are reviewed to ensure proper installation up to this length.
When flexible ducts are located outside the conditioned space, they should be sealed to prevent loss of conditioned air and also insulated to prevent thermal loss or gain from the ambient air. All ducts, whether rigid or flexible, should be sealed with UL-181–rated duct mastic.
PVC ducting is the cheapest one available, but is highly versatile and can be used in the majority of general ventilation connection applications, including cooker hoods.
Exception: Ducts for domestic kitchen cooking appliances equipped with down-draft exhaust systems shall be permitted to be constructed of schedule 40 PVC pipe and fittings provided that the installation complies with all of the following: The duct is installed under a concrete slab poured on grade.
Rectangular duct is fine for range hoods but not the best option because of its proneness to grease buildup.
The proposed code language
It says, “Length limitation: Factory-made flexible air ducts and connectors should not be more than 5 feet (1,524 mm) in length and shall not be used in lieu of rigid elbows or fittings.”
The only way to truly distinguish between the two products is to examine the label on the product. An Air Duct has a rectangle or square within the label whereas the Air Connector will have a circle within the label (shown below in red).
Which type of duct should not be allowed to pass through walls? Flexible duct connector.
Too often, flex ducts are not installed properly, and they end up kinked, bunched up, undersized, or sagging. These issues can cause increased resistance in the duct system, resulting in too little airflow reaching a building's heating and cooling equipment.
When flexible ducts are installed in unconditioned areas of the home, they should not be squeezed into any cavities that are smaller than the outer diameter of the duct, including the duct insulation; in conditioned space, they should not be installed in cavities smaller than the inner duct diameter (ENERGY STAR).
Measure the length and width of the room where the flex duct will be supplying the air. Multiply the length and width together to get the square footage of the room. For example, a 10-by-10 room will be 100 square feet.
If cold air is coming down your range hood vent, install a backdraft damper. A spring-loaded damper is the most reliable. If you already have a backdraft damper, check if it is bent or damaged. Also, make sure that the damper is grease and grime-free.
A vented microwave range hood is a microwave with a fan that is ducted to the outside. Air passes through some type of filter inside the fan (often charcoal filters). Then, it travels through ductwork outside your home.
Lower the front of the microwave and have a look over the top, under the cabinet. The unit will be supported at the lower rear by a bracket flange. Your microwave's vent either exhausts upward or rearward, but from right at the top rear of the unit. You'll be able to see whether there's a duct opening at that location.