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Hey Ed, Is It Better to Size up or Down When It Comes to Ductwork?


In This Edition of “Hey Ed,” Ed Discusses Is It Better to Size up or Down When It Comes to Ductwork

Hey Ed, is it better to size up or down when it comes to ductwork? It's always going to be up. There is no scenario where you can put in a duct that is too large. If you've got somebody telling you that they're putting in a specific size duct because they're trying to keep their velocity up. Don't take advice from that person on pregnancy relationships or finances because they don't know what they're talking about. Our perpetual struggle when it comes to duct sizing is to make sure that we keep our velocity down. In fact, the conclusion to manual D says something to the effect of there's a lot of things to consider when we're sizing duct airways low velocity is not one of them. What makes a system function properly is ducts that are large enough to support the velocity or not exceed our velocity maximum but a properly sized supply outlet covering or supply register that's where the magic happens if you will. Picture a hose. Hold your thumb over the end of it. I don't care if the hose is this big around or this big around. As long as the proper volume is coming through that hose, our thumb being over the end of it is our supply register and that supply register is going to dictate the throw and spread that comes out of it. You're never going to have a scenario where your ducts are too big and that's the way I see it.

In This Edition of “Hey Ed,” Ed Discusses Is It Better to Size up or Down When It Comes to Ductwork

Ed Janowiak is the Manager of HVAC Design Education at ACCA.


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Posted In: Hey Ed, Technical Tips

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