The Latest from the Energy Vanguard Blog

An older house with ducts located in the third worst place you can put them
Posted by Allison Bailes on August 14, 2019
Ah, so many choices.  If you want to design and install a duct system to create problems, the possibilities are endless.  I've certainly written about a lot of them (as well as how to do it properly).  Today, though, let's focus on one particularly bad place to put a duct.  In fact, I think it's...
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What's the best velocity for moving air through ducts?
Posted by Allison Bailes on June 26, 2019
The first thing to know about the velocity of air moving through ducts is that the slower you get the air moving, the better it is for air flow.  That was the main point of my last article.  In fact, the title asked the question, "Is Low Velocity Bad for Air Flow in Ducts?”  And the answer was that...
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What is the best velocity for air moving in ducts?
Posted by Allison Bailes on June 12, 2019
It's obvious that moving air too quickly through ducts can be a problem.  Faster air means more turbulence, more resistance, and more noise.  But I run into people who think that low velocity also can be a problem in ducts.  Just recently I heard someone talking about how low velocity causes "...
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What criteria should you use to determine when is the best time to change the filter in your HVAC system?
Posted by Allison Bailes on May 20, 2019
One of the topics I've hammered on for years is the inadequacy of using rules of thumb for sizing air conditioners.  The standard one ton of air conditioning capacity for each 400 to 600 square feet of conditioned floor area just doesn't work.  We know that a load calculation based on how a...
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Using a high-MERV filter doesn't have to result in a large pressure drop
Posted by Allison Bailes on April 23, 2019
Last August I began a series of articles on filtration and indoor air quality.  You can find the list of them at the bottom of this article but let's do a quick review here:  We spend a lot of our time in buildings.  A lot of indoor pollutants are generated in the kitchen and not removed by the...
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Aprilaire high-MERV filter with carbon
Posted by Allison Bailes on November 9, 2018
What is a hair's breadth?  A strand of the finest human hair is about 20 micrometers (also called microns) in diameter.  Take a piece and slice it in half.  Then take one of those halves and slice it in half again...and then one more time.  Now you've got a sliver of hair that's 2.5 microns wide. ...
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What happens to the air flow in ducts when the size changes?
Posted by Allison Bailes on October 29, 2018
As we continue our study of indoor air quality and filtration, we now come back to duct design.  Today's lesson is on an interesting bit of physics that applies to anything that flows.  It could be heat or particles or electromagnetic energy.  In our case, it's air, a fluid, and the physics we're...
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Filter bypass because of incorrectly installed filter
Posted by Allison Bailes on October 24, 2018
Indoor air quality (IAQ) researchers have established that little bitty invisible pieces of stuff that float around in the air are bad for human health.  Of course, being scientists, they don't call it little bitty invisible pieces of stuff.  They call it particulate matter (PM) or particulates. ...
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Friction rate is the wronge name
Posted by Allison Bailes on October 12, 2018
Last year I wrote some articles on duct design and one of the topics I covered was this thing called friction rate.  At the end of that article, I discussed "How to think about friction rate."  It confuses a lot of people because it's the wrong name.  First I'll tell you why and then I'll tell you...
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HVAC School logo
Posted by Allison Bailes on August 24, 2018
I love to share good resources and here's one you need to know about if you're interested in the nitty gritty of HVAC systems.  I'm talking about HVAC School, with their various channels like their daily Tech Tips email, YouTube videos, quizzes, and a podcast.  It's all free. Bryan Orr (shown below...
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