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NORA Advanced Air Flow

furnace manufacturer’s specifications, choose a furnace that gives a 50º–70ºF rise with a 65,000 Btuh rating. Using a 60ºF rise (which is in the middle of the manufacturer’s specifications), the formula looks like this: CFM = 61,000 CFM = 61,000 1.08 x 60 64.8 CFM =941.35 The duct system would need to have a minimum capacity of 941cfm to meet the heating requirements of the building. Air ducts can be made from many different materials. The most common are galvanized sheet metal, fiberglass ductboard and flex duct. Galvanized Sheet Metal For many years, galvanized sheet metal had been used exclusively. Sheet metal duct can be Galvanized Sheet Metal Flex Duct round, square or rectangular. All three types are often used in a single duct system. Because of its smooth interior surfaces, sheet metal offers the least amount of resistance to airflow of any duct material and sheet metal ducts are also the most durable. Because of the cost of the material and labor to install sheet metal ducts, other types of materials have become popular. 12 National Oilheat Research Alliance Fiberglass Ductboard The inside of surface of fiberglass ductboard is coated with plastic or a similar coating to Fiberglass ductboard prevent the release of the duct fibers into the airflow. This creates a rough surface resulting in friction loss greater than found in sheet metal ducts. Fiberglass ductboard is quieter than sheet metal duct because the ductboard absorbs blower and air noises better. Flex Duct Flexible round duct comes in sizes up to 24″ in diameter. Flex duct is typically used in spaces where obstructions make rigid duct difficult or impossible. Flex duct is popular because it is competitively priced and easy to install. Unfortunately, it is often installed incorrectly. Common difficulties found with flex duct installation include: tight radius turns, improper support, improperly stretched runs and compressed runs. Flex duct is quiet because its soft sides absorb sound. However, the soft


NORA Advanced Air Flow
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