Derek ColeGM, Simmons One Hour Heating & Air · AI HVAC Answers

Proper Duct Sizing for Improved Airflow and Pressure #shorts

24 Sept 2026 · 1 min

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1:18

In this short instructional video, Derek Cole explains a common HVAC problem in many homes: insufficient airflow in distant rooms caused by improper duct sizing. He points out that commercial establishments like Zaxby's or Red Robin use a "reducing" strategy, where duct dimensions decrease progressively along the trunk line, ensuring adequate air pressure reaches the farthest registers. Cole contrasts this with typical residential installations that often keep ducts too large, leading to pressure loss and weak airflow in back or side bedrooms. He uses a water‑hose analogy—covering the hose tip increases pressure and spray distance—to illustrate why maintaining pressure is crucial. The key takeaway is that ducts should be sized to gradually reduce, following engineered drawings, to keep pressure up and deliver consistent airflow throughout the home.

Chapters

And that is a problem in most homes we've gone to. So if you go to like a Zaxby's or a Red Robin and you look up above in the ceiling, you'll see the duct system. And what you'll see is a properly sized duct. You'll see it going big, small, smaller, smaller, all the way down. That's called reducing. That is a proper way to do it. That way the air pressure gets all the way down to the end of that run Of trunk line so you can have air at the end. That is the proper way to do it. That's the way we do it. That's the way it should be done. Any engineered drawings you see, that is the way it's done. And that is a problem in most homes we've gone to because the back bedroom or the side over here is not getting the airflow well. It's because the pressure has dropped. And if you think about it, it's kind of like a It's kind of like a water hose. If you have the water hose at home and you just, you know, set it there, turn the water on, the water comes out, kind of drips out. If you put your thumb over the outlet, it'll spray a lot further, right? Same situation. It's because of the pressure. So air is just like water and should be treated that way. So you want to make sure you keep the pressure up.