![]() The main way that air is lost in rectangular ductwork is through the seams and joints. That’s a 50% reduction over the best outcome you can expect with rectangular ducts! Because it is practically airtight, and with many options for coupling and sealing the end-to-end joints, spiral ducts can often have as little as 1 to 2 percent overall air leakage. But through meta analysis in the HVAC industry, the spiral-seamed duct came into being. With some improved methods for connections, a rectangular system might have as little as 3 to 4 percent leakage. For many years, it was difficult to obtain less than 10 percent leakage in rectangular ductwork. The second efficiency advantage of spiral ductwork over rectangular is that air loss is much less with spiral. Smaller surface area means less resistance to air flow and less strain on the air handler. Screws are kept to a minimum due to fewer and better sealing joints. The seams are on the outside and there are no square corners or creases, providing a smoother surface for the air to travel. ![]() Why Spiral is Better: In a spiral duct, there is no internal seam to restrict air flow. When that happens, efficiency goes down, and the life expectancy of the components is also decreased. Yes, but it makes the air handler – or fan – that is pushing the air work harder. These all increase the static pressure inside your HVAC system. So here are at least four types of restriction that meets the air flowing through rectangular ducts: seams, creases, screws and greater surface area. Even if all else were equal – which it is not – the surface area of rectangular duct is more than in an oval or round spiral. In comparison, the perimeter of a spiral round duct of equal volume is only 41 inches, or about 15 percent less. A 12 X 12-inch rectangular duct has a perimeter of 48 inches. These factors all add resistance to the air flowing through rectangular ducts.ĭo the Math: A final way that resistance to air flow is found in the rectangular duct is by the fact that there is more surface area in a rectangle than a circle having the same area. Also, a rectangular duct usually has shallow diagonal creases in each of the sides to stiffen the duct and prevent it from flexing when the air turns on and off. When the duct is assembled, the seam is often secured by the use of screws. Rectangular ducts are often transported to the job site unassembled as flat stock because it is easier to load them in a truck and they take up less space. Depending on how it was made, it might even have two seams in opposite corners running along its length. Seams, Screws and Creases, Oh My: A rectangular duct has a seam that runs its entire length. Static pressure refers to the resistance that faces both the air flowing through the system and the components of the system itself. Here is one area where spiral ductwork is superior to rectangular because it minimizes static pressure. Just as blood flowing through our vascular system can be restricted by various kinds of blockages, so can the air in our HVAC system be restricted by features inside it. Whether we’re talking summer or winter, cooling or heating – we want air to flow through the ductwork smoothly and efficiently. In your HAC system, air flowing through the ductwork with as little hindrance is what it’s all about. ![]() There are several reasons spiral ducts are better. Here is our reasoning and the conclusion we’ve made in the rectangular ductwork vs spiral ductwork debate. We wouldn’t make a statement we can’t back up. ![]()
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