PCD Installation Guide – Underground Ducts Install Above Water Table The PCD duct system is not designed to be waterproof. Installation must be made safely above the water table.
Ducts should not be placed where water infiltration may occur. Depth The top of the duct can extend into the cement, leaving a minimum of 2 ½” of cement above the top, or the duct can be placed well below the cement. However, the duct should not be placed so deep that the weight on it will exceed the load capabilities. Trenching and Backfill After the excavation has been made, no special bedding need be used for PCD Duct.
It can rest right on the ground, or be set in sand or light aggregate. Pea gravel or sand (or the material taken from the trench, if equivalent) can be used to backfill.
Spread the backfill material evenly around the duct making sure there are no gaps, and tamping in place is a recommended practice. No cement is needed to fill in around the duct, since the tamped fill holds the duct in place and the plastic coating prevents ground corrosion of the galvanized steel.
This plastic coating is resistant to any minerals or salts that may be in the backfill soil. PCD Duct will not “float” when backfilled to within 2” of the top of the duct. Concrete is then poured so that all “tie-down” work is eliminated. CAUTION: When backfilling or grading, care should be taken not to dump or push heavy loads directly on the duct, nor should heavy equipment be allowed to run over the duct.
It can be crushed under thoughtless abuse. Large Diameter Ducts Special care should be taken with large diameter ducts. Backfilling and tamping should be done without damage to the ducts. Temporary bracing can be used inside the ducts or angle rings can be permanently installed on the ducts to provide strength and rigidity.
Rings should be primed and coated with PCD paint. Polyvinyl Coated Ductwork Load Specifications #1 Standard 4” – 8” 400 lbs./Linear Ft.
10” – 12” 600 lbs./Linear Ft. #2 Corrugated 14” – 36” 1800lbs./Linear Ft.All ducts 14” or more in diameter are corrugated for extra strength. Where deeper burial or heavier loading is required duct gauges can be increased. Also angle rings and/or special bracing can be used.
I've written a lot about duct problems, especially those in flex duct because they're so abundant. A couple of years ago, I even wrote an article about whether or not. My answer was no but that we need better quality control. When I updated and reposted the article recently at, Jack Lagershausen, the executive director of the, sent me a letter. Unlike 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 of their installation guide,.
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 encourage every HVAC company installing flex duct to invest the $15 and get a copy. Then use it to train your installers. A few tidbits from the ADC standards 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. Basically, what they tell you is not to do all those things I've shown here in this blog and how to install flex ducts properly. They also refer to standards from other organizations (ACCA, ASHRAE, ASTM.) because this is an installation guide, not a complete reference work. For duct sizing, they refer you to ACCA's Manual D, for example. One interesting bit of info that many installers need to understand is that flex ducts need to have the inner liner pulled tight. If it's not tight, the friction rate jumps significantly, and that means the air flow takes a hit.
The diagram below shows that if a flex duct has even 15% longitudinal compression, the friction rate doubles. With 30% longitudinal compression, the friction rate quadruples. 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 an equal size duct inside the turn as shown below, they say you're OK. 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' per foot of length between supports. The supports need to be at the manufacturer's recommended spacing, but no longer than 4' maximum. The straps that hold up the flex duct need to be no less than 1.5' wide. 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. One more little note about those connections: The first method they show is to connect the inner liner mechanically with a metal clamp, the kind shown at right. I've never seen one of these in the field, except on a couple of my own installations.
They also show how to attach the inner liner with sheet metal screws. The fastener that's used most often, plastic zip ties, is only mentioned in the footnotes: 'Nonmetallic clamps shall be listed and labeled in accordance with standard UL 181B and marked '181B-C'.' How to get even better performance with flex duct The ADC standards provide good guidance for duct installers. If someone follows them perfectly and the system is commissioned properly, it should work just fine.
The problem, though, is quality control, and one way to help with that is to make it a little harder to do sloppy work., 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, at least follow the. 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 just posted an article about, 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 buck. Of course, Robert's Canadian, so you'll have to convert using the current exchange rate if you're here in the US.;) You really should because Mr.
Bean is one of the most knowledgeable HVAC guys around. Check out the rest of his website, too. There's a wealth of information there.
The bottom line in all this is that you get what you pay for. Related Articles. A few comments: 1)Mike McFarland is absolutely right, whether you intend to do a turn in the flexduct in the manner ideally described in the manual, it will never turn out that way. Everytime you have to do from a straight bend of over 20 degrees, use a metal elbow. You can't do both streach out the ducts and get good radius bends at the same time. 2) If the ducts run through the attic DON'T HANG THEM They need to lay on the ceiling joist or bottom cord, streached out and insulation heaped over them. Remember they really should have more insulation than the ceiling.
3) Don't use temporary tape (also called duct tape) to connect the flex duct inner liner to the metal takeoff, elbow, or register boot. 4) Use mastic at every joint, metal to metal and metal to plastic. John Poole: Well.well.he IS Mr. Bean.;) Now did you finish applying the Canadian-to-US exchange rate to his table? John Proctor: Great advice. There's one caveat to your attic suggestion, however. Heaping insulation over the ducts is fine in dry climates but can cause condensation on the duct insulation jacket in humid climates.
The DOE's Building America program recommends BEDs - buried, encapsulated ducts. By spraying closed cell foam on the ducts before burying them in attic insulation, you prevent the condensation problem. Great post Alison! While we prefer sheet metal, especially for trunk lines, large duct systems can be exorbitantly expensive if done in all metal. There are times where flex duct (or sections of it) can help to reduce costs. In our retrofit work, we'd rather see a customer with a well design and installed duct system where flex is used appropriately, then have the homeowner keep a poorly designed and installed duct system because they can't afford the cost to replace it with sheet metal.
The 'zip ties' you referred to work very well IF they are tightened behind the first rib of the duct (with mastic applied to the sheet metal connection). Hand tightening of nylon ties won't do the job. The only way to secure them consistently is to use a tensioning tool. These use a ratcheting mechanism to fully tighten the tie, and then cut it flush. No slipping - ever. They are required tools for all of our installers (required to have them AND to use them). As long as flex duct is sized right (Manual D and a flex duct calculator), and installed right - less than 1/2' sag, long radius bends (if any), and tight, sealed connections - it can work well.
I salute you sir, Over the years, I have seen remarkable things on construction sites.major load carrying wood beams cut nearly in half to accommodate ductwork and my favorite.the ductwork seems to be the easiest place to throw trash, construction waste and even concrete. If you are a brave soul, if you ever get the chance, use one of the television camera snakes to explore what is in the ductwork of many homes and commercial buildings. As was once said: 'We have met the enemy and they is us!' Living in a hot humid climate, I see the issues caused by lying duct on insulation on attic floor. Hanging flex with mininum sag with 3' duct wrap is easier said than done. I've always watched closely the guys who do it well and learned from them.
Always -2 people to run flex. Just to open the bag of flex & streach the inner liner is impossible for 1 person to do alone. Always- mastic.paint on mastic or mastic tape. Always -3' duct strap.wider width trumps narrow width and when properly suspended the 3' will not cause the duct to compress reducing air flow. Always- 90 degree ells at supply boxes. Always- test duct for air leakage.
Having killed the kracken & replaced it with ductwork that both performs & moves proper cfm of air, takes time, experience & the want to do it right. Most hvac companies have low man on the job installing ductwork. No room in the bid for the time to do it right. I stumbled into ductwork repair/change out,by testing before and after ducts were sealed by hvac companies. Some cases duct leakage & air flow were worse than before the work was done. So, I learned.
Once the homeowner understands that the 30% duct leakage is air they pay to heat and cool that simply isn't making into the living area.they understand. Next areas to address are oversized supply box pentrations, supply boxes that lift off the attic floor when supply grill is installed, and return air leakage. If testing of ducts/returns was code this would be a step in the right direction.
As difficult to achieve as getting hvac companies to actually train their workers how to install ducts. But in that perfect world.duct & return systems would be sealed tightly and the sham of duct cleaning, uv lights, and air purification systems would die out. Good article.thanks. When the latest (3rd) edition of Manual D was in development, there was a lot of discussion about friction rates of poorly installed flex. Texas A&M;, having studied this, provided data from its research for inclusion in the manual, the idea being to give designers an idea of real-world friction rates, and hopefully persuade diligent contractors to follow recommended installation practice.
I should point out that the ADC lobbied heavily to keep this data out of the book, but in the end, the data was included as Appendix 17. Adam G.: Yes, if you're using zip ties, you absolutely have to have the tensioning tool. Even with pliers, you just can't get it tight enough. David R.: Yeah, it's amazing the kind of stuff that finds its way into ducts.
See the photo I recently shared on. Debbie: Good advice. I agree with you about wider support straps being better. As with most minimum standards, they're the least you should do. Going above and beyond usually works better. Stan: Yeah, I think nylon zip ties do have a shorter life in hot attics. I don't know what their estimated life is, but the first thing to do is try to get ductwork into conditioned space.
Ryan S.: Yeah, I don't think I'd want to hold flex duct to a connector with those screws either, now that I think of it. Now that I think about it, I don't think I've seen it done in the field, either. David B.: Thanks for the inside info. It's nice to know that the data made it into the manual, despite their lobbying against it.
Technical standards and manuals developed by SMACNA members have worldwide acceptance by the construction and code community, as well as local and national government agencies. ANSI, the American National Standards Institute, has accredited SMACNA as a standards-setting organization. SMACNA standards and manuals address all facets of the sheet metal and HVAC industry – including duct construction and installation, indoor air quality, energy recovery, roofing and architectural sheet metal, welding, and commissioning. Technical Inquiry SMACNA develops and publishes more than 30 technical documents with more being added to the library each year and several in review and revision cycles. In accordance with SMACNA Policy, a formal interpretation of the literal text of SMACNA's technical manuals, guides or standards is available but only on the basis of written request or inquiry.
The request must pertain to a specifically identified portion of a SMACNA technical document that does not involve published text which already provides the requested information. In considering such requests, SMACNA will not review or judge products or components as being in compliance with the document or publication. FILTER. News Patrick J. Brooks, MBA, PE, new senior project manager with SMACNA’s Technical Resources Department, brings more than 30 years of industry experience to SMACNA National. With his extensive knowledge, Brooks is an exceptional resource for SMACNA members and staff.
News SMACNA contractors actively engaged in hands-on learning about SMACNA’s most prominent standards during SMACNA’s two-day Technical University held in April at the Sheet Metal Contractors Association of Philadelphia and Vicinity’s new chapter headquarters in Warminster, Pennsylvania. News In addition to developing and issuing highly regarded industry standards, SMACNA’s Technical Services Department continuously fields questions about technical aspects of sheet metal construction and the application of specific SMACNA standards. News SMACNA technical staff presented sessions about two technical manuals at the 2018 AHR Expo, in Chicago in January.
News Approximately 50 Bay Area SMACNA contractors learned about key SMACNA standards and the latest technical apps during SMACNA’s recent Technical University at the Bay Area Training Center in Oakland, Calif. News One of the most frequently asked architectural questions SMACNA receives is on sizing gutters and downspouts. In response, SMACNA’s Technical Resources Department has created a free Downspout and Gutter Sizing Calculator. News The second edition of SMACNA's “Thermoset FRP Duct Construction Manual” is now available. The 228-page book is an authoritative resource that design engineers, industrial engineering departments, pollution control authorities, FRP manufacturers, and installation contractors can use for the proper selection, manufacture, and installation of FRP duct systems.
News The revised “Round Industrial Duct Construction Standards,” 3rd edition, 2013, an American National Standard, ANSI/SMACNA 005-2013, is now available. SMACNA members will receive an email shortly with instructions on how to receive their gratis copy. Technical Paper SMACNA’s Technical Resources Committee completed wind uplift testing on custom-fabricated fascia and coping architectural elements constructed in accordance with the SMACNA Architectural Sheet Metal Manual. News SMACNA’s first edition of the “Phenolic Duct Construction Standard” provides basic phenolic duct fabrication and installation standards that sheet metal contractors, code officials and design engineers will find useful.
It is a new American National Standard. News Round industrial duct construction calculations just got a whole lot easier for SMACNA members. News Now there’s an app for SMACNA’s “Round Industrial Duct Construction Standard” (RIDCS). This powerful app, available today, is actually Web-based. Best of all it is free to SMACNA members.
Click here to access the App. Scroll to “SMACNA’s Round Duct Construction App.” Login to your member’s only account and you will automatically arrive on the App landing page. News With the long-term rising cost of fossil fuels, reducing the energy consumption of HVAC systems is increasingly important.
ACTEX Exam P Study Manual, 2016 Edition ACTEX Exam P Study Manual, 2015 Edition ACTEX Exam P/1 Study Manual, 2012 Edition, 1st Printing. Actex p 1 study manual 2016 edition.
News TU-DSC00584-200Approximately 50 participants from SMACNA member contractors learned about SMACNA’s most prominent standards at SMACNA’s Technical University in Milwaukee, Wis., on Sept. Technical Paper Achieving uniqueness in building construction should start at the top. When choosing a roofing style, many architects choose custom fabricated metal roofs. SMACNA's Custom Fabricated Sheet Metal Roof Test Report describes the performance of the double lock standing seam and batten seam metal roof conforming to the SMACNA Architectural Sheet Metal Manual.
Webinars SMACNA and the National Energy Management Institute (NEMI) are presenting a webinar on the NEMI HVAC Fire Life Safety certifications exclusively for SMACNA members only on Jan. 26 at 11:00 a.m. Webinars Event Objectives Gain solid understanding of how to construct duct in a resource efficient and sustainable manner that is compliant with SMACNA’s HVAC Duct Construction Standard. This is the final session in a three part series. Webinars Event Objectives Gain solid understanding of how to construct duct in a resource efficient and sustainable manner that is compliant with SMACNA’s HVAC Duct Construction Standard.
This is the second session in a three part series. Webinars This presentation will cover the following (with respect to rectangular duct): - Basic definitions used to properly describe rectangular duct - Limits and proper application of various joints and seams - Use of the manual to determine proper construction options - and more. Webinars Session highlights the considerations in specifying and installing fire dampers, smoke dampers, combination fire and smoke dampers and ceiling dampers in HVAC systems.
Webinars Session highlights the SMACNA Seismic Restraint Manual – Guidelines For Mechanical Systems 3rd Edition (ANSI) means and methods for seismically bracing ducts and pipes to meet the requirements of the regionally appropriate seismic hazard levels so that ducts/pipes are more likely to maintain their integrity and remain attached to the building’s structure during a seismic event. Webinars This webinar presentation on duct air leakage will define what duct air leakage is and how it relates to equipment air leakage, accessory air leakage, and HVAC system air leakage. Webinars This webinar will demonstrate how to use SMACNA's Third Edition of the HVAC Duct Construction Standards to determine the proper range of construction options of rectangular duct used in today's commercial market. Technical Paper The Master Index provides contractors, design professionals, and code officials with a centralized resource of SMACNA technical documents. The index includes key words or phrases from all SMACNA technical standards, manuals and guides. Technical Paper As an organization with contributing members on the National CAD Standard (NCS) Committee, SMACNA is committed to improving electronic communication between members of the architect/engineer/contractor (AEC) community, and the overall quality of construction. Technical Paper SMACNA is being increasingly advised that contractors are being required to provide elements of fire damper and combination fire/smoke damper installations which are both unnecessary and not allowed.
Specifically we refer to requirements to seal the retaining angles to the wall/floor fire rated assembly and to other directives to fill the expansion space with materials such as mineral wool, ceramic fiber or firestopping caulks. Technical Paper This technical paper contains ERRATA for the Guide for Steel Stack Construction, Second Edition 1996. Please download and include this listing of changes/corrections with your copy of the manual and reference it as needed. Technical Paper This technical paper reviews the Model Building Code process of the International Code Council (ICC) and National Fire Protection Association (NFPA) Building 5000 Code and addresses SMACNA National's position with regards to the efforts of the code community to develop a single set of comprehensive and coordinated national codes.
4×1 PVS for Underground Duct Systems Polyvinyl Duct (PVS) Sheet Metal Connectors, Inc. PVS spiral pipe is formed from a coil of metal into a rigid PVC tube with a 4-ply spiral lockseam. It has smooth interior for low friction loss with the grooved seam entirely on the outside. This pipe has a resistance to crushing approximately 2 1/2 times that of longitudinal lockseam. Optional corrugations are available which increase the rigidity of the pipe by approximately 300%. Pipe sections can be joined together by an E-Z Flange with Barrel Clamp, E-Z Flange Jr. With Barrel Clamp, or Standard Spiral Pipe Connector.
Single-Wall Materials General The use of PVS Ductwork eliminates the need for encasing in concrete. Because no additional concrete is required, savings can be considerable. By combining the strength of steel and the chemical inertness of plastic, PVS Ductwork is lightweight as well as corrosion and weather resistant.
PVS ductwork will not rust, chip, crack, peel, corrode or produce odors. Although light in weight,PVS Ductwork is strong enough to walk on and will not collapse under concrete. PVS Ductwork is specified by more engineers and architects than any other underground HVAC duct system.
Durability PVS ductwork is a rugged, durable material that will take ordinary shipping and handling without damage. PVS ductwork needs no protection in earth from sand, concrete or plaster. It is not affected by the minerals and salts found in normal backfilling materials. PVS ductwork has also passed thousands of accelerated salt spray and humidity cabinet tests with no loss of adhesion or corrosion resistance. It can be cut and formed with regular sheet metal equipment and tools with no harm to the coating. Even the largest diameter ducts are easily cut with portable metal-cutting saber saws or circular saws. Connections E-Z Flange Jr.
With Barrel Clamp – 6” to 24” Diameter The E-Z flange jr. Is a 5/8” flange turned out 90° on each end of the spiral pipe and fittings. The installer applies a gasket on one flange, mates the two flanges together, and attaches the barrel clamp.
For field cuts a 5/8” flanged sleeve is available, cut the spiral pipe to the measured length and apply the sleeve.For dimensional data please refer to the E-Z Flange Specification Manual. E-Z Flange with Barrel Clamp – 26” to 96” Diameter The E-Z flange with barrel clamp can be factory installed or shipped loose for field installation. A set consists of two E-Z flanges and one barrel clamp. For field installation the installer attaches the E-Z flange to the pipe and fittings.
Next the installer applies the gasket to one flange,mates the two flanges together and attaches the barrel clamp. SMC also installs E-Z flanges.
Flanges are fastened and internally sealed on all ends of the spiral pipe and fittings.For dimensional data please refer to the E-Z Flange Specification Manual. Standard Spiral Pipe Connector Pipe to Pipe connections are made by using a fitting size coupling that slips inside the mating pipe sections, as shown. A stop bead runs around the middle of the coupling to center the coupling in the connection.
Secure the connection by installing sheet metal screws through the outer shell of the duct, 1/2 inch from the stop bead. PVC Underground Fittings Sheet Metal Connectors, Inc. PVC fittings and connections are fabricated in 1 x 4 or 4 x 4 material to protect against corrosion from soil. SMC PVC fittings are manufactured with an elbow lock seam or standing seam. SMC fabricates PVC fittings in most sizes and configurations using our state of the art equipment.
All joints and connections should be sealed in accordance with SMC’s recommendations to assure an air tight system.The PVC fitting dimensional data listed in the PVC Specification Manual is for slip fit type connections only. For E-Z Flange PVC fitting dimensional data refer to the E-Z Flange Specification Manual.
All PVC fittings can be manufactured with: E-Z Flange with Barrel Clamp – 26” to 96” Diameter E-Z Flange Jr. With Barrel Clamp – 6” to 24” Diameter Standard Spiral Slip Connector Sealing Spiral pipe and fitting slip connector joints must be sealed to prevent air leakage and to keep dirt and sand out of the duct system. PVC Tape is recommended as it is ideal for this usage. It has superior adhesive qualities, even in extremely hot or extremely cold weather. Also as an insurance factor, PVC Duct Sealer No.
8 is available. This is a flexible and self-curing air pressure sealant.
This can be applied from one-gallon cans by brush application. It provides a positive sealing of joints and screw holes. PVC Duct Sealer No. 8 may also be obtained in a cartridge package.
Sheet Metal Installation Instructions
Approximate coverage is 375 linear feet per gallon at a 1/4” bead.PVC tape is not required for the PVC Spiral Pipe System.