![]() ![]() Round Metal Duct CFM Chart : Round Metal Duct SizeĨ5 CFM at 0.06 friction loss or 115 CFM with a 0.1 friction loss. Terminology tip: Friction Rate and Friction Loss refer to the same measurement. Metal ductwork is tried and true, and it serves the system well when it is wrapped to eliminate air leaks and insulated to protect system efficiency. The size will be either 6” or 7” depending on the friction rate. If there isn’t an exact match, go up to the duct size. It will be found in different columns depending on the friction rate. Using the chart, you’ll see that for a 12” round flex duct, maximum CFM is 480 CFM or 500 CFM depending on the friction rate.įind the CFM closest to 115 in the table above. Typcially, the max cfm for 6 inch duct is 80 cfm. Round Flex Duct CFM Chart: Round Flex Duct Size You might get incorrect results using a calculator designed for metal if you’re installing flex, for example.įAQs below the table answer common sizing questions. Pro tip: Remember to use a duct calculator for the kind of duct you are using. The numbers are those you would obtain using a duct calculator, aka a ductulator. This flex duct size and CFM chart covers all common sizes at two friction rates. And if it is compressed, not fully stretched, airflow will be negatively and significantly affected. The downside is that it can be more easily damaged and doesn’t last as long. Round flex duct is easy to work with and typically comes insulated for convenience. This leads to slightly different results in the duct sizing tables. They are slightly different due to a small variance in friction rates. Now, let’s examine the ductwork CFM chart for round flex and round metal duct. OK, we covered that simply to make sure that we’re all on the same page. In the example above, if total CFM is 1500 and the room needs 12% of that, the room needs a duct that can carry 180 CFM. To determine needed CFM per room or zone, multiply the % for each room by the total CFM for the HVAC system.For example, if the total load is 34,000 BTU and the room load is 4,100, its percentage is 0.121 or 12%. Each room’s percentage of the total – the formula to determine this is to divide the room load by total load.Total load for the home or building in BTUs.What’s the formula? As a refresher, it is assumed that you have used Manual J and/or related software to determine: We’ve used the formula for duct sizing and compiled quick, at-a-glance tables for you to use as you design your own or a client’s ductwork. ![]()
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