The Next Best Thing Since Sliced Bread!!!!

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Or not.  I stumbled upon this little ad when I was looking for a good price on the foam I use to build Duc-Blocs.  I’m sure that the good folks who spent many tens of thousand of dollars developing this product and brining it to market understand the concepts of Manual D and Manual T (not to mention S, RS, H, P, – oh, yes – and J).  Hopefully they weren’t just pandering to granny’s and uncle Joe’s desire to muck with the airflows in each and every room of the house.  Ay, caramba.  My next post will be a discussion of the “Four Schools of Thought on Where to Stick a Supply Register in a Room”.  Until then, can you guess what they are?

Here’s a little quiz question to dwell on: What’s better for heating a room, floor registers or ceiling registers, and why?



Conditioned Crawlspaces



This is NOT a good way to condition your crawlspace.

There is a lot of confusion out there about the purpose of conditioning crawlspaces.  In other words, why would you want to?  From my (biased) perspective, the MOST IMPORTANT reason to do this would be to get your ducts inside the conditioned space.  If the ducts are not in the crawlspace, all the other reasons make it a tough sell.

So, this got me to thinking.  What would the ultimate conditioned crawlspace look like?  First, I would start with a single story home with really tall, super-insulated walls, say ten feet, and an insulated slab on grade floor.  Then I would install all of the supply ducts right along the concrete floor. Once they were all in, I would install a removable metal grid floor so that it just clears the largest diameter duct.  Granted, this would look strange, but the point is that now any losses from the ducts would certainly benefit the conditioned space.

You would still want the ducts to be properly sized, well sealed, and reasonably insulated.  If the ducts leaked, the air would not be going to the register where the air was intended to reach.  This is not so much an energy issue as it is a comfort issue.  The BTU’s are still inside the conditioned shell, it’s just that they are not where they are supposed to be when they are supposed to be there.  This may result in very small temperature variations between rooms.  If you think about it, though, when is the airflow ever perfect?  NEVER!  Even if you balanced the system down to the exact CFM at every register.  There is no single set of room-by-room airflows that is perfect.  The ACTUAL room by room loads on a house vary as the sun moves through the sky, as people move around a house, as lighting and appliances are turned on, and as doors and windows are opened and closed.

So, condition that crawlspace, make sure it is clean and well insulated, let it communicate with the house, don’t freak out over sealing (or insulating) the ducts, and size those ducts right!

Happy Trails,


Bubba’s Cooling Units

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I’ve decided that I need a new unit to help me teach air conditioning concepts.  Everyone knows what a BTU is, right?  British Thermal Unit.  Those snobby, sophisticated little units of heat that are about the same as a wooden kitchen match.

So, what happens when you take a stream of cold air and blow it into a warm room?  Are you “adding coldness” to it?  No!  Any good BTU Geek will tell you that you are displacing BTU’s in the room air by diluting them with air that has less BTU’s, at a rate determined by the heat capacity of air and the volumetric flow rate of the entering air, blah, blah, blah.  I lost you already, didn’t I?

What does an air conditioner really do?  They are rated in BTU’s, units of heat, not units of coldness.  Well, yes, they extract heat from the air, but how is that really different than adding coldness? Who’s to say that we aren’t adding coldness to the room?  Who made that law?

So, to better understand air conditioning and cooling, I’m proposing a new unit.  I call it a BCU, which is short for “Bubba’s cooling unit”.  I call it that because it is not sophisticated, but it gets the job done.  From now on if someone asks me how much cooling something needs, I’m going to tell them in BCU’s.  When I teach people about cooling, I’m going to explain it in terms of adding BCU’s.

Wish me luck with that.


Welcome to My New Blog

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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.

Stay tuned!


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