Debunking Common Duct Design Myths

By Chris Fogarty

Do you know as much about ductwork as you think you do? Duct design is a critical element of an HVAC system, but the topic of ductwork is often overlooked in our industry. With our new Residential Duct Design technical training class, you'll learn the right way to design and install duct systems in your customers' homes to ensure maximum efficiency and comfort.

Here's the truth behind five common duct design myths.

  • MYTH: Flex ducts handle the same volume of air as metal ducts. Our industry uses flex ducts all the time because they're inexpensive and quick to install, but their corrugated makeup is more restrictive than that of metal ducts. Using flex ducts in a system designed for metal ducts can cause airflow problems and potentially generate more callbacks.
  • MYTH: The "400 CFM per ton of cooling rule" can be used anywhere in the country. Most contractors assume that a certain size air conditioner requires a certain amount of air without considering the relative humidity of the area. Measuring humidity is an essential step in determining adequate airflow, and our BuildATech® class can help you understand how to effectively measure humidity.
  • MYTH: Return air grilles "suck." Return vents don't actually suck air in. Instead, we pressurize the room to push air into the return grilles. Without correct duct placement and sizing that creates a direct path, the system will not move air efficiently.
  • MYTH: Variable-speed (ECM) motors can offset poor duct design. ECM motors do have more power, but pairing one with a poorly designed duct system will only cause repeated motor failures and other problems for the homeowner.
  • MYTH: Always use 0.10 IWC to size ducts. Friction rate is not a "one size fits all" number. The amount must be calculated at each house to determine the correct rate for duct sizing.

You can see why, with so many myths floating around about duct design, we found it necessary to create a new Residential Duct Design class. In it, you'll learn how the duct system works with the overall HVAC system. Not only will you dive deeper into the above myths and other ductwork challenges, but you'll also have the chance to design your own duct system. Check out our class schedule to find one of these not-to-be-missed sessions near you.

Guest blogger Chris Fogarty has been with Lennox Industries for 18 years and currently heads the BuildATech® program.

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