The purpose of this blog is to communicate to everyone who may be interested in learning more about the things I know a bit about.

  • HVAC Design and Diagnostics
  • Home Energy Rating Systems
  • California Energy Codes
  • Training for all of the above.

Thank you for stopping by.  Please click the “Follow” link to receive notifications when I post new discussions.


p.s. I have another blog for my sci-fi/nature/adventure writing, in case you are interested: Russ King, Author


7 Comments (+add yours?)

  1. Chris Norris
    Jun 07, 2014 @ 06:30:53

    Great articles! Thanks!!


  2. Dave Johnsonnola
    Feb 03, 2022 @ 15:14:04

    Your mistaken post Vegas covid illness brought me here.

    Now following.

    Get well soon!


    • Russ King
      Feb 03, 2022 @ 15:58:41

      LOL. Thanks, Dave. Muc appreciated. Join us on Thirsty Thursdays for a two hour discussion of HVAC design topics focused around Kwik Model 3D software, on the first and third Thursdays of each month (usually). Details at the Kwik Model Facebook Page or the Kwik Model Users Facebook Group.


  3. Jerry Rivers
    Jun 05, 2022 @ 09:17:37

    Hi Russ,

    I just found your page while searching for some HVAC info. Such amazing information I can follow and understand. I assume your introduction to hvac class is no longer available? as the link doesn’t work. I was wondering about a part 2 of one of your blogs: duct size vs. air flow – part 2. I read part one and part 2 is definitely the exact information I need for the home repairs I am doing to my home. Is there a link to this particular blog that I am just missing?

    Thank You,

    Jerry Rivers


    • Russ King
      Jun 05, 2022 @ 12:01:32

      Hi Jerry. Glad you like the blog. That’s exactly why I write it. The recorded version of the training can be found here: https://www.youtube.com/channel/UC7HM3nJWOE5_Om0nMBfKj7w/playlists One class is introductory and the other is more advanced.
      Part 1 of the duct size vs airflow ended up just being a teaser to buy the book. HVAC 1.0 – Introduction to Residential HVAC Systems, available on Amazon. Part 2 is in the book.


  4. wesley
    Aug 17, 2022 @ 17:51:09

    Love your articles. Very informative. However for the life of me, in all my years of doing hvac/r I have never seen it a good idea to do an entire system solely in flex duct.


    • Russ King
      Aug 17, 2022 @ 19:28:52

      Hi Wesley.
      Thanks for your comments. I’m curious what you mean by “never seen it a good idea”. Avoidance of flex duct is surprisingly common, but I have to wonder if it is based on any actual test data and not just on hearsay or from seeing flex duct systems that “look” bad. I know for a fact that some of the biggest and most outspoken anti-flexers are contractors who a bid a project in sheet metal and lost out to a flex duct bid. I can tell you this: I have designed over two thousand residential HVAC systems. They were almost all production homes. Not only did we design the systems, but we tested them after they were installed. They tested out great and we had no design-related complaints. Many are still going strong 30 years later.

      People will say that sheet metal flows better. Size for size, sure, but not a lot better. A 7″ flex duct will flow better than a 6″ sheet metal, so it’s hardly an argument against flex. In my opinion the only knock against flex is that flex duct is more prone to poor installation (crimping, crushing, excessive length, etc.), but that’s not the fault of the material. You have to wonder how much of that is because the owner of the install company allowed very inexperienced techs to install the ducts because they know flex duct is easier to install. Also, you see a lot of people posting pictures of flex systems that look terrible, but no one actually tested them. I’ve tested sheet metal ducts that looked spectacular, but tested out terrible. As I’ve said before, a well designed flex system is very forgiving to airflow and can handle some crimping and crushing. The key is a good Manual D design. (That’s rare for any kind of duct material.) As long as it has good airflow, is tight, and well insulated, I don’t care how it looks behind the sheet rock. It can be tied in knots for all I care. I hope you’ll give flex a chance. I would love to see two identical houses side by side. One flex and one sheet metal. A lot of people would automatically say the sheet metal house was better, but until they actually test it, they are just guessing. Forming a strong opinion based on guesswork doesn’t reflect well on someone’s knowledge of a topic. Thanks again for you comments!



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