The size of your kitchen exhaust duct should be based on the square footage of your kitchen.
The most common sizes are 8″ and 12″. For kitchens that have the smaller square footage, we recommend an 8″ vent stack.
Do you know Standard kitchen exhaust duct sizes?
Choose ducting that’s the same size as or slightly larger than the vent opening. The more powerful the hood, the larger the duct. For instance, a typical 400-cfm unit requires a 6-inch duct, while a 1,200-cfm model needs a 10- to the 12-inch duct.
The standard kitchen exhaust duct size is 4 inches in diameter. This is the size used by most homes and business establishments for over 50 years. While it may be adequate, there have been significant advances in technology that can improve its performance and allow kitchen exhaust fans to run quieter without sacrificing airflow.
The main problem with a 4-inch pipe is that it has a low resistance to airflow so the fan must work harder than required to move the volume of air needed through the system.
The result is an increase in noise when compared with modern-day 6″ HVAC ducts which are more efficient at flowing air with less back pressure or obstruction. For this reason, 6″ PVC or ABS ducting should be considered when replacing older smaller systems in order to achieve greater performance benefits.
The 4-inch size is adequate for most kitchen installations but if you have a large commercial cooking operation with multiple appliances, upgraded ducting may be required.
Standard tubing capacity can range from 800 to 1100 CFM.
These figures are based on 100% extraction of the air inside the building and do not take into account the volume of outside air that must be brought in by infiltration or exfiltration. The more complicated your installation, the greater the importance of carefully considering all aspects before finalizing your design.
This is even more critical if your kitchen exhaust system will serve more than one space such as an office building. Ductwork should always be sized according to its maximum theoretical load (the at which it ceases to extract any more air) versus its actual load (the at which it ceases to bring in any more air).
Standard Kitchen Exhaust Duct Sizes
Cutting openings in masonry walls can be difficult (if not impossible) due to their structural rigidity and use of resilient materials like metal lath or tile backer board. It is recommended that you consult with a professional contractor experienced with these types of buildings before attempting this yourself.
Furnace/stove work must allow for removal of old flex-ductwork, installation of new aluminum foil shielded 6″ PVC ducting, and support any weight from the newly installed ductwork. In some cases, it may be necessary to reinforce the floor below the furnace/stoves to support the added weight from the upgraded ducting system if it contains more than two runs or elbows.
If your existing 4-inch system already contains several sections of larger diameter pipe, it is recommended that you leave the heavier sections in place and add new lightweight sections on each end.
Measure joist spacing to ensure ducting will not be blocked by floor trusses or beams.
Your local building code should provide guidance on this. If your 4-inch system is already made up mostly of large diameter pipe (48″, 60″and 72″) most codes may allow it to remain without modification, depending on its existing condition and purpose which primarily includes providing adequate airflow for smoke removal in case of a fire.
It is also important that all openings around the interior perimeter of exterior walls are sealed with high-temperature silicone caulk or canned expanding spray foam before installation is complete. This ensures there are no gaps between the existing building envelope and interior wall finish which could cause condensation problems if the air inside your kitchen is significantly hotter or colder than that of adjacent space(s).
The overall pressure drop of a system, including all fittings, will affect its capacity. A rule of thumb is to allow 1″WG (water gauge) on each inch of pipe length for every 90 feet. This value might need to be adjusted higher depending on conditions.
Ducting must always maintain a slope upwards using either adjustable hangers or hardware designed for this purpose on the return side of the system to avoid suction drawdown due to gravity. Keep downslopes within 8% whenever possible as steeper grades can cause more resistance and reduce capacity.
Standard Kitchen Exhaust Duct Sizes (cre: thisoldhouse)
How do you measure kitchen exhaust duct size?
Kitchen exhaust fan duct sizing calculations are mostly based on the volume of air produced by the kitchen range hood. The table below lists approximate exhaust volumes for several different types of common kitchen appliances.
Remember that these figures are average ranges and may vary according to model type, efficiency, installation conditions, and other factors. To determine the required duct size you need to use outside or inside static pressure test kit (in North America this is known as a “CFA Kit”).
How big should my Kitchen Exhaust Fan be?
If your kitchen has two appliances that produce an exhaust volume in the 125 to 175 range then your fan should have a capacity of about 1100 cubic feet per minute. To calculate this we multiply 125 by 2 and then add 175: 125 x 2 + 175 = 450 + 175 = 625 so we round up to 650 cfm. The formula for determining the exact required exhaust volume is:
Volume = Appliance 1 + Appliance 2 + …… + Appliance n x Max Efficiency where each appliance has a different maximum efficiency. In our example above, Max efficiency is 100% of all appliances are running at full capacity. If only one of two appliances were running then the maximum efficiency would be somewhere between 50 and 100%.
Kitchen hoods with more than three draw-in appliances should have automated variable speed control to maximize energy savings and maintain peak performance.
To calculate your fan’s cfm rating for a given static pressure you need to use a “CFA kit” (Conductance Fan Airflow or Static Pressure Test Kit). This test measures how much air will pass through the duct under given pressure and tells you exactly how large or small your exhaust fan needs to be.
Kitchen Exhaust Fan Duct Sizing: CFM to Inches Wg Conversions
To determine the required Kitchen Exhaust Fan size using standard residential ductwork, simply use the following formula: Orifice Area (square inches) = 1090 x cfm / 100 then round up to the nearest standard inch size.
For example, an 800 cfm kitchen range hood would require an 8″ diameter duct which is just slightly larger than most flat 4″ round down-swept kitchen vents.
A 1000 cfm fan would need a 10″ or 12″ round duct while 2000 cfm or greater may require 14″ or 16″ round duct.
Standard Kitchen Exhaust Duct Sizes (cre: HVAC)
Kitchen Exhaust Duct Design: Inside Wall Diameters, Angles, and Corner Joints
For kitchen exhaust systems with inside wall diameters of 8 inches or less, a simple 90-degree elbow will generate the necessary static pressure to ensure proper operation.
You can use a manifold roof cap as the first elbow as long as you make sure to use two 90 degree elbows on the “inside” wall (the ceiling side). In this type of installation, it is important to make sure the fan is mounted level so that laminar airflow is maintained.
Keep in mind that for every bend or fitting you add between an 8″ duct and the appliances you cut down on its efficiency by approximately 15%.
Kitchen range hoods that are non-recirculating (vent to the outside) require much larger ductwork and a sealed airtight boot or damper door that will close off the kitchen when the fan is not in use.
Kitchen Exhaust Duct Design: Outside Wall Diameters, Angles, and Corner Joints
For kitchen exhaust systems with outside wall diameters of 10 inches or less, a simple 120-degree elbow will generate enough static pressure to ensure proper operation.
In this type of installation, it is important to make sure the fan is mounted level so that laminar airflow can be maintained.
Keep in mind that for every bend or fitting you add between an 8″ duct and the appliances you cut down on its efficiency by approximately 15%.
Kitchen range hoods that are non-recirculating (vent to the outside) require much larger ductwork and a sealed airtight boot or damper door that will close off the kitchen when the fan is not in use.
Kitchen Exhaust Fan Duct Sizing: CFM to Inches Wg Conversions
To determine the required Kitchen Exhaust Fan size using standard residential ductwork, simply use this formula: Orifice Area (square inches) = 1090 x cfm / 100 then round up to the nearest standard inch size.
For example, an 800 cfm kitchen range hood would require an 8″ diameter duct which is just slightly larger than most flat 4″ round down-swept kitchen vents. A 1000 cfm fan would need a 10″ or 12″ round duct while 2000 cfm or greater may require a 14″ or 16″ round duct.
Kitchen exhaust duct materials
Kitchen exhaust ducts must be made of a specific material. For most kitchen exhaust systems, the only allowable materials are metallic (galvanized or stainless steel, or copper), and aluminum ducts are not allowed.
What are the best materials to use for my kitchen exhaust duct? I want to build one out of 4″ aluminum pipe. Any ideas where I could find some good plans for this, or is it even possible? Thanks!
It creates an energy-efficient air passage with minimal restrictions on airflow. We can custom-build your ductwork at your plant using our telescoping segments, which permit us to work around obstacles that would be impossible to handle with conventional curved sections. The material made for telescoping ductwork should always be smooth, clean, and dry for proper operation.
As a result, the telescoping material should be clean and free of “flashings” or other debris that could hinder smooth telescoping action. The wall thickness should be uniform in all directions. If the joints are not tight, leakage will result in reduced suction; rough or dirty surfaces may cause excessive air turbulence or blockage of flow.
Standard Kitchen Exhaust Duct Sizes (cre: basc)
The Materials
Galvanized steel (gauge 22) Aluminum R=3/16″ Thickness .015″ to .040″. Stainless Steel AISI-304 (gauge 24) Aluminum R=1/8″ Thickness .035″ to .060″. Stainless Steel AISI-316 (gauge 26) Aluminum R=1/8″ Thickness .035″ to .060″.
Aluminum Ducting Aluminum Flex Duct
Another material we use for our Telescoping Ductwork is Metalbestos flexible duct. Metalbestos Flexible ductwork as well as working as an air-tight telescoping joint, also provides the best insulation that you can get in a commercial kitchen exhaust system.
The Metalbestos Flexible duct easily telescopes into place and conforms perfectly to the uneven contours of your structure’s ceiling and walls, and unlike heavy rigid metal systems and other semi-rigid or flexible metal products, has no seams or joints where air leakage will occur. The product is lightweight, easy for even one person to handle, and lighter than a rigid metal duct, so it’s easier to handle. The telescoping action makes installation fast and easy, with no need for an assistant.
Metalbestos® flexible pipe is produced in 20-foot lengths out of galvanized steel with aluminum fin stock attached to both sides of the outer wall by an adhesive applied at the factory. Standard Metalbestos® flexible pipe includes one layer of insulation within the wall thickness that acts as a dust barrier; this layer may be left out upon request, which will result in a slight reduction in overall R-value.
Steel Flex Duct Stainless Flex Duct
Our standard telescoping joints are constructed using two (2) steel or aluminum fin stock panels (gauge 22 or 24), assembled under heat and pressure, with a rubber gasket between the two flanges.
The fin stock is formed to provide maximum strength and stiffness, while its smooth surface facilitates telescoping action and prevents air leakage between joints.
Aluminum Flex Duct Stainless Flex Duct
We at Telescopingducts.com offer our customers the following materials for their Kitchen Exhaust Systems: Aluminum Flex Duct, Stainless Steel Flex Duct, Mini Rectangular Metallic Pipe (RMP), Metalbestos Tube Sheets, Galvanized Steel 16D Pipe, Alcoa’s Aluminum Angle.
Conclusion
The size of the exhaust duct in your kitchen will depend on the type and number of appliances you have. A range hood with a fan is typically needed for an oven, stovetop, or cooktop that has more than four burners. If you don’t have a range hood, then plan to get one when installing your new ventilation system so it matches up correctly.
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