![]() ![]() SPIDA and SMACNA jointly sponsored and funded a study, performed at Tennessee Tech University, titled “Determine the Maximum Negative Operating and Collapse Pressure of Stocked Spiral Duct With and Without Corrugations.” This study focused on the limited range of “stock” spiral duct being produced by SPIDA members with diameters up to 42”. As a further question, has much of the toilet exhaust, ducted return and general exhaust in commercial HVAC construction been designed and installed as rectangular duct because a heavier (and more expensive) spiral duct has been required? SPIDA finds this highly questionable since positive pressure product has undoubtedly been used for negative pressure applications with good results. Yet, if you look at the SMACNA negative pressure tables, there is only a very small range at which you can use this stock spiral duct.Īs this table shows, stock spiral duct should only be used in sizes up to 16” diameter at a maximum -2” WG and only to 10” diameter (12” diameter if you have minimum 26 gauge stock) at a maximum -4” WG. No doubt, plenty of stock positive pressure spiral duct has been used for toilet exhaust systems with no adverse consequences. The nature of “stock” is that material is taken for use without control by the manufacturer on where and how it is used. For those, the SMACNA HVAC Duct Construction Standard has separate tables, Tables 3-10 and 3-11, for minimum gauges. These systems are seldom designed for negative pressures greater than -2” WG or tested at greater than -4” WG. Commercial HVAC systems often have toilet exhaust, ducted return air and general exhaust systems. Those are generally higher negative pressures and their construction is covered by the Industrial Ventilation Manual and the SMACNA Round Industrial Duct Construction Standards. This round stock can be used for virtually all commercial HVAC supply, outside and makeup air systems.īut what about negative pressure applications? We’re not talking about fume hoods, dust collectors and industrial exhaust. The use of 28 gauge material is allowed through 14” diameter per this standard, though most SPIDA members use 26 gauge in those sizes because of material availability, durability of product and some local codes mandating a minimum 26 gauge for commercial construction. This gives not only the advantage of lower cost from duct produced more efficiently, it also greatly reduces lead time by using products that can literally be acquired “same-day.”Ī survey of SPIDA members indicates that stock spiral duct is usually made in accordance with gauges for up to 10” WG positive pressure in accordance with the Sheet Metal and Air Conditioning Contractors' National Association (SMACNA) HVAC Duct Construction Standards. A high percentage of an HVAC duct system could be installed using “stock” rather than cut-to-length or custom duct. Fabricating “stock” is highly efficient and results in minimal waste. These are fabricated not only for their own use, but may also be inventory for reps, secondary distributors or contractors. US Duct offers more duct types and connection options than any other industrial duct manufacturer.Spiral Duct Manufacturers Association (SPIDA) members often fabricate an inventory of standard lengths of round spiral ducts. are simply constructed to accommodate the spiral pipe. The connection ends of branches, elbows, gates, etc. ![]() Most of the non-pipe components used in conjunction with spiral pipe are constructed using the same methods (sheet metal manufacturing) as those used with flanged duct, airtight tubing, and clamp together duct. Pipe sections can be joined together by using inset-off-set with barrel clamp, standard spiral pipe connectors, sheet metal screws, or special angle rings. Typically, spiral duct is available in any length and although longer lengths of pipe do reduce the number of connections that need to be made during installation, the cost of shipping such long sections may make it more expensive to deliver. It has a relatively smooth interior for low friction loss with the grooved seam entirely on the outside. Where most other types of ducting are formed from sheet metal, spiral duct pipe is formed from a coil of metal into a rigid steel tube with a 4-ply spiral lock seam. Ducting Options from US Duct Clamp Together Duct, Flange Ducting, US Tubing, and Spiral Duct ![]()
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