My A ccount | Free 10-day GBA Pro Trial | Sign out My GBA Glossary Store Contact Us Ducting Supplies BudgetHeating.com Budget Priced DuctWork Wholesale Prices To The Public How to Install Flex Duct Properly He lpful? 0 + - Following the Air Diffusion Council's standards would lead to better installations PO STED O N MAR 13 2013 BY A LLISON A . BA ILES III, PHD, GBA A DVISOR www.EcoCleanMechanical.com 100% Customer Satisfaction Call- Free Estimate 720-299-7782 (especially those in flex duct) because they're so abundant. A couple of years ago, I even wrote an article in the Energy Vanguard Blog about whether or not flex duct should be Subscribe to the Building Science RSS feed: Plain RSS . My answer was no — but that we need better quality control. myYahoo recently here at Green Building Advisor, Jack Google Our Blogs Lagershausen, the executive director of the Air BUILDING SCIENCE Diffusion Council , sent me a letter. Image 1 of 5 Unlike a certain, very large company that a while back, the Air Diffusion Council was smart about it. He admitted that the problems I wrote about are "far too common," and sent me a complimentary copy BUSINESS ADVISOR Many flex duct installations leave a lot to be desired. By following the installation standards ENERGY SOLUTIONS of the Air Diffusion C ouncil, you'll ge t be tte r re sults. You can still do be tte r, though. of the Council's installation guide, Flexible Duct Performance and Installation Standards myA OL Bloglines After I updated and reposted the article threatened me www.HomeAdvisor.com Find Top-Rated Pros In Your Area. Enter Your Zip & Get 4 Free Bids! Air Duct Cleaning Denver I've written a lot about duct problems banned Local Furnace Experts . Today, with the hope that some readers will act on this information, I'll give you a bit of an overview of this guide, and will encourage HVAC companies looking to do a better job of installing flex duct to invest the $15 and get a copy. Then use it to train your installers. GREEN BUILDING NEWS GREEN ARCHITECTS' LOUNGE GREEN BUILDING BLOG GREEN BUILDING CURMUDGEON GUEST BLOGS A few tidbits from the ADC standards MUSINGS OF AN ENERGY NERD The 25-page guide begins with a description of the classifications and characteristics of flex duct, then discusses how they're tested, listed, reported, and certified. Chapter 4 is where the meat of the manual is — the installation details — and that's the part I'll talk about here. NEIGHBORHOODS/COMMUNITIES Q&A SPOTLIGHT Basically, what the Council tells you is not to do all those things I've shown in my articles, and how to install flex RELATED ARTICLES ducts more or less properly. They also refer to standards from other organizations (ACCA, ASHRAE, ASTM...) because this is an installation guide, not a complete Should Flex Duct Be Banned? reference work. For duct sizing, they refer you to ACCA's Manual D, for example. Raining, Dripping, Crying Duct Boots Keeping Ducts Indoors Pe te r Yost is the Dire ctor of R e side ntial Se rvice s for BuildingGre e n, LLC in Brattle boro, Ve rm ont. He has be e n building, re se arching, Pull the inner liner tight One interesting bit of info that many installers need to Why Don’t More HVAC understand is that flex ducts need to have the inner liner Contractors Own Duct Leakage pulled tight. If it's not tight, the friction rate jumps Testers? significantly, and that means the air flow takes a hit. The Duct Leakage Testing About the Authors diagram below shows that if a flex duct has even 15% longitudinal compression, the friction rate doubles. With te aching, writing, and consulting on high pe rform ance hom e s for m ore than twe nty ye ars. R e ad m ore ... Sealing Ducts: What’s Better, Tape or Mastic? 30% longitudinal compression, the friction rate Jose ph Lstibure k is a principal of quadruples. Building Scie nce C orporation An interesting side note to this part of their standard is inve stigate s building failure s that when Manual D was being revised for the third and is inte rnationally re cognize d . He is a fore nsic e ngine e r who edition, the ACCA Manual D group wanted to include information about how poorly installed flex duct affected friction rates, using data from Texas A&M’s research on the topic. According to David Butler, “the ADC lobbied heavily to keep this as an authority on m oisture re late d building proble m s and indoor air quality. R e ad m ore ... data out of the book.” ACCA overrode their lobbying, however, and included the data as John Straube , Ph.D., P.Eng., is a Appendix 17. principal of Building Scie nce C orporation and a profe ssor of building scie nce in the C ivil Engine e ring De partm e nt and Don't make sharp bends Another problem that I see frequently is bends that are too sharp. The ADC standards say, "Keep bends greater than or equal to one (1) duct diameter bend radius." The language is a bit clunky, but the diagram below shows what they mean. If you can put School of Archite cture at the Unive rsity of W ate rloo, C anada. Dr. Straube has acte d as an e ducator, re se arche r, consultant and e x pe rt witne ss on e ne rgy e fficie ncy, durability and IAQ . C urre nt inte re sts include the optim al syste m an equal size duct inside the turn, as shown below, they say you're OK. (You can see my de sign of buildings, sustainable buildings, and thoughts on this below.) m oisture proble m avoidance . Allison Baile s III has a PhD in Use proper supports to prevent sagging physics. He is also a R ESNET- Another biggie that I see all the time is sagging ducts. The official recommendation from the ADC is that flex ducts should sag no more than 1/2 inch per foot of length between supports. The supports need to be at the manufacturer's recommended spacing, but no longer than 4 accre dite d e ne rgy consultant, traine r, and the principal of Ene rgy Vanguard , a consulting firm in De catur, Ge orgia. feet. The straps that hold up the flex duct need to be no less than 1.5 inch wide. How to make connections Related Content The ADC standards give a lot of other details about installation, including one of the most important aspects: the connections. The skinny on that is to make sure you get a good, solid connection between the inner liner and the connector, seal it with mastic or tape, and then bring the insulation and outer jacket over the connection and seal it, too. From around the site HVAC Equipment Can Overpower Wind and Stack Effect IN GR EEN BASIC S How to Install Flex Duct Properly One more little note about those connections: The first method they show is to connect the IN BLO GS | MAR 13, 2013 inner liner mechanically with a metal clamp. These are the ones you see holding the rubber How to Choose the Right Mechanical System hoses onto their connectors in engines, with a screw that you turn to make them tighter. I've never seen one of these in the field, except on a couple of my own small retrofit installations. IN BLO GS | FEB 28, 2013 Good Ducts, Bad Ducts They also show how to attach the inner liner with sheet metal screws, but I wouldn't do that IN BLO GS | FEB 26, 2013 with flex. The 7 Biggest Opportunities for HVAC Contractors Interestingly, the fastener that's used most often, plastic zip ties, is only mentioned in the IN BLO GS | FEB 6, 2013 footnotes: "Nonmetallic clamps shall be listed and labeled in accordance with standard UL A Buyer's Guide to Bath Fans 181B and marked '181B-C'." IN FINE HO MEBUILDING Cheaper Hot Water IN FINE HO MEBUILDING Water Heaters: Tank or Tankless? How to get even better performance with flex duct IN FINE HO MEBUILDING The ADC standards provide good guidance for most duct installers. If someone follows them perfectly and the system is commissioned properly, it will probably work fine. The problem, Home Remedies for Energy Nosebleeds IN FINE HO MEBUILDING though, is quality control, and one way to help with that is to make it a little harder to do sloppy work. Mike MacFarland , a home performance contractor in California, wrote what may be the best advice ever given in a comment here in the Energy Vanguard Blog: The trick to getting these installations right is to use rigid ductwork for all "deviations from straight," then pull the ductwork taut between the two ends which now point towards each other. The big advantage over a full rigid installation is sound control — the installations are quieter than fully rigid ones. There you have it. Use flex duct for the straight runs and hardpipe everywhere else. If you really can't bring yourself to buy those sheet metal elbows Council standards , at least follow the Air Diffusion . A word about cost The main reason we see so many bad installations is expense. It costs more use the right methods. It costs more to train employees to do it right. It costs more to use materials that are harder to mess up. It costs more to do proper design and commissioning. The truth is that there are costs associated with doing it wrong, too. It's just that the homeowner usually bears those costs. My friend Robert Bean recently posted an article about the cost of HVAC systems , which he prefers to call indoor climate systems. The chart below is from that article and gives you a feel for how much bang you're getting for your Join our Facebook Posse! buck. Of course, Robert's Canadian, so you'll have to convert using the current exchange rate if you're not in the Great White North. ;~) You really should go read his article Find us on Facebook GreenBuildingAdvisor.com because Mr. Bean is one of the most knowledgeable Like HVAC guys around. Check out the rest of his website, too. There's a wealth of information there. 4,054 people like GreenBuildingAdvisor.com. The bottom line in all this is that you get what you pay for. Allison Bailes of Decatur, Georgia, is a speaker, writer, energy consultant, RESNET-certified trainer, and the author of the Energy Vanguard Blog . You can follow him on Twitter at @EnergyVanguard . F acebook social plugin News TAGS: A IR DIFFUSION COUNCIL, DUCT, DUCT INSTA LLA TION, DUCT LEA KA GE, DUCT TIGHTNESS, DUCTWORK, FLEX DUCT, HVA C, MA NUA L D New England Will Get Two New HighPerformance Housing C ommunities Walgreens Plans a Net-Zero Store ‘Active House’ Makes U.S. Debut Market for Green Building Materials to Grow Passive House Training Streamlined Southface Energy Institute Hosts the Greenprints C onference Passive House NW C onference is C oming Soon Image Credits: Energy Vanguard Air Diffusion C ouncil Building Green Robert Bean Erik North: Energy Auditing Blog PRINTER-FRIENDLY Like SHARE Marc Rosenbaum: Thriving On Low Carbon EMAIL THIS PAGE Marcus de la Fleur: Reshaping Our Footprint 7 people like this. Sign Up to see what your friends like. Eco Build Trends Almost Passive House Up Hill House 1 Texas Sustainabliity Blogspot COMMENTS Engineering a Better World Blog greenbridge.wordpress.com 1. SUN, 03/24/2013 04:05 flex duct installation riles-files.blogspot.com by Brian Nelson We install a lot of HVAC systems on Martha's Vineyard, ranging from mini-splits to fully ducted. On the ducted projects, we use turninghoustongreen.com He lpful? 0 + - flex for the branch runs to the supply boxes. We keep those flex runs short - on the order of 5 to 15 feet. It is critical to remove the flex from its box, extend it to its full length of 25', and ensure that the inside and outside shells are fully extended together. As the flex is fully compressed in the box and shipped cross-country, invariably the inner shell gets bunched up and misaligned with the outer shell. If the installer doesn't fully extend the flex assembly first, it is common to get too much inner shell in the first half of the flex, leading to air flow issues. Connecting the inner shell to the supply box and the supply takeoff using the large zip ties is essential, then foil taping the inner shell, then pulling the outer shell over the supply take off and taping this with foil tape. This process takes a bit more time but the consistent air flow results are worth it. In my house, I used no flex (a bit nuts - turning vanes on all rectangular changes of direction, rigid duct to all supply boxes) and it is noisier than systems we install with flex - with no substantial loss in air flow at supply outlets. Brian Nelson, M.S.M.E. Nelson Mechanical Design, www.nmdgreen.com Edit C om m e nt ehaugsjaa.wordpress.com kitchen-exchange.blogspot.com greenbuildingindenver.blogspot.com thegreenspotlight.com TimEian.com nbsuperinsulatedhouse.blogspot.com Musings & Mutterings of a VT Architect Trillium Architects' blog Post new comment Colonial Green Products Your name: Brian Nelson Colonialgreenproduct… Spray foam Insulation experts Experts at saving energy for life Subject: HERS Raters of MA Comment: * greaterbostongreen.c… RESNET Certified Builder Approved! Stretch Energy Code Consulting Discussion policy: The editorial staff at GreenBuildingAdvisor.com does review user submissions. Please be respectful of others. Inappropriate content will be removed. Filtered words will be replaced with the filtered version of the word. Web page addresses and e-mail addresses turn into links automatically. 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