The Latest from the Energy Vanguard Blog

Insulation on flex duct (Photo by Mike MacFarland, used with permission)
Posted by Allison Bailes on February 13, 2018
If you know a little building science, you've no doubt seen a lot of problems that occur with air distribution systems. Ducts just don't get anywhere near the attention they deserve in most homes, partly because they're hidden from view. I've written about ducts quite a bit here and have shown...
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Are door undercuts sufficient as return air pathways?
Posted by Allison Bailes on October 23, 2017
Most people don't know that simply closing a door in their home can make them sick, increase their energy bills, or reduce their comfort. We live in this invisible stuff called air. We pull many pounds of it into our lungs each day. A typical air conditioner, heat pump, or furnace easily moves 20...
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Perfect Balance in-door return air pathway
Posted by Allison Bailes on October 17, 2017
Your bedroom really doesn't aspire to be a balloon. Yet, because of the way your heating and air conditioning system was installed, it may be acting like one. At least to an extent. It doesn't expand the way a balloon does, but it does get blown up. Think about it. If your bedroom has a supply vent...
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Making third-party HVAC design work
Posted by Allison Bailes on September 28, 2017
What if a builder refused to build from plans drawn by an architect? What if a tile installer refused to implement designs handed to them and instead did their own thing? What if an HVAC contractor told a potential client they wouldn't install a system designed by a third party to ACCA protocols?...
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Flex duct presentation intro, 2017 Buildng Science Summer Camp
Posted by Allison Bailes on August 8, 2017
One week ago I spoke at the Westford Symposium on Building Science. You may know it better as Building Science Summer Camp, since that's what everyone calls it. I wrote up a little summary of the whole conference last week but didn't say a lot about my presentation. Today I'll fill you in on what...
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Duct design schematic diagram showing vents and air flow
Posted by Allison Bailes on June 9, 2017
To this point in our little series on duct design, we've been calculating intermediate quantitites: available static pressure, total effective length, and friction rate. Today we use all that to find out how big the ducts need to be. We're following the Manual D protocol for duct design, a standard...
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UL and Intertek partner with home builders in new home energy rating program for Florida
Posted by Allison Bailes on June 8, 2017
In case you didn't see the announcement out of Florida, two big well-known names have entered the market for home energy ratings and energy code compliance. Underwriters Laboratories (UL) and Intertek are working with the Florida Home Builders Association (FHBA) certify home energy ratings, blower...
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Friction rate can be used in a duct calculator to size ducts
Posted by Allison Bailes on June 1, 2017
Today's installment in the duct design series is a simple one. It's just a straightforward calculation that gives us the design friction rate from the two quantities I discussed in my last two articles. In part 2, I told you about available static pressure (ASP). In part 3, I covered total...
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Length and equivalent length in duct design
Posted by Allison Bailes on May 30, 2017
Today we move another step down the road of duct design. I started the series with a look at the basic physics of air moving through ducts. The short version is that friction and turbulence in ducts results in pressure drops. Then in part 2 I covered available static pressure. The blower gives us a...
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Static pressure measured with a magnehelic pressure gauge
Posted by Allison Bailes on May 26, 2017
In part 1 of this duct design series, I discussed the basic physics of moving air in ducts. Now we're going to take that and use it to figure out how to make all the parts work together properly. First we choose a blower that will give us the total air flow we need. Then we design a duct system...
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