#manual d

Tech Tips:

Under Pressure
A few weeks ago, I was hired to consult on a multi-family new construction project.  The building was already framed, and the ducts were roughed in.  The owner of the building was concerned with the quality of the ductwork.  He noticed that the HVAC company was not following the mechanical engineer's plans. This was my […]
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What Airflow Goes Around HAS to Come Around
Have you ever woken up early on a Saturday morning and thought to yourself, “I really wish I knew how to size transfer grilles and jumper ducts properly?” I know I have. Although come to think of it, I believe it was a Friday morning.  Properly sizing transfer grilles is something I have been wanting […]
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Does your Kitchen Exhaust Suck?
Have you ever been tasked with installing the exhaust duct for a kitchen hood?  I have, and when doing so, I wondered how to size the duct run correctly. Since I had a basic understanding of how airflow works, I knew that there had to be a limit on the resistance the fan can handle; […]
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Equivalent Length Merry-Go-Round
I recently read a tech tip by Matt Bruner about using the Manual D process. In the article, he designed a duct system for a small job using a ducted mini-split. One thing I noticed about his design was that the supply and return duct velocity was fairly low compared to the arbitrary 900-feet-per-minute supply […]
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Manual D Speedsheet Walkthrough
Bryan recently released a podcast on rules of thumb and how they can really get us in a pickle with sizing ductwork. With that in mind, I thought this might be a good time to do a walkthrough of Manual D from start to finish on a project I just finished up. My good friend […]
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Homeowner’s Guide to Sizing an AC System (and who is responsible when you’re uncomfortable)
This tech tip was a collaborative effort between Matt Bruner, Adam Mufich, Ed Janowiak, and Genry Garcia. Thank you to everybody who gave their input! The next time you come across a homeowner who wants a bigger HVAC system, or you simply want to set expectations for a customer, share this tech tip with them. […]
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The Friction Rate Chart (and What it Means)
A lot of proper duct design comes down to an understanding of available static pressure and friction rate. We've covered this topic several times on this site and the podcast, but I wanted to focus on this ACCA chart specifically (shown above). If you want a deep dive, I highly recommend listening to my podcast […]
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Podcasts:

Common Duct Design Mistakes w/ Jack Rise (Podcast)
In this episode, Jack Rise talks about duct design regarding ACCA manual D, friction rate, face velocity, duct velocity, and what is ACTUALLY wrong with flex duct. Manual D causes a lot of confusion for technicians, and most techs have a limited understanding of it anyway. When determining a blower wheel for commercial ductwork, Jack […]
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