10/5/2023 0 Comments Spiral duct ventsLocate the exhaust terminal at least 3 feet from any door or window and away from the fresh air intake of a high-efficiency furnace, water heater, or any other HVAC intake.The ducts should be joined with clamps or foil tape, not screws or similar fasteners that can protrude into the inside of the duct and trap lint. Short, direct, semi-rigid metal transition duct is preferred. The transition duct should be UL-2158A listed and should be no longer than 8 feet. At the interior wall, connect the exhaust duct to a transition duct that connects directly to the dryer.Support the duct at least every 12 feet, and at all joints.Any joints should be installed in the direction of air flow. This length should be decreased by 2.5 feet for every 45-degree bend the duct makes and 5 feet for every 90-degree bend the duct makes. The exhaust duct should be rigid metal 4 inches in diameter and no more than 35 feet in length or as specified by the duct manufacturer. Install a rigid metal (aluminum or galvanized steel) exhaust duct connecting the transition duct to the exhaust duct outlet terminal.There are several commercially available products or this inset can be constructed on site with 2x4 blocking, drywall, and tape and mud to air seal the seams ( Bailes 2010). This inset allows the connecting duct to be straight and not be crushed or looped behind the dryer in ways that severely restrict air flow and can cause a fire hazard from trapped lint. When installing the interior duct terminus in the laundry area inside the home, consider using a telescoping rigid metal transition duct or installing an inset box in the wall where the dryer will be located to allow space in the wall cavity for the connecting duct to come up from the floor to the port on the back of the dryer. When the clothes dryer is not installed at the time of occupancy, the exhaust duct opening inside the home should be capped or plugged and marked as “dryer duct, future use.” If the dryer duct is run through walls where nails or screws from finish carpentry or other work are likely to penetrate the ducting then protective steel sheet metal plates (≥ 1.6mm) should be installed on the finished face of framing members where there is less than 1.25 inches between the duct and the finished face of the framing (2009-2018 IRC M1502). No screen should be installed in the duct terminus (IRC M1502.3, see Compliance tab). ![]() A louvered damper is more effective than a single hinged door. The duct termination should be fitted with a closeable gravity or automatic damper. ![]() The exhaust duct should terminate outside the building at least 3 feet from any building opening and at least 10 feet from an AC or heat pump condenser. Screws or similar fasteners that can protrude into the inside of the duct and catch lint must not be used. The ducts should be joined with clamps or foil tape. The transition duct (the visible piece of duct connecting the dryer to the wall) can be up to 8 feet and should be listed in accordance with UL 2158A there are some semi-rigid metal transition duct products that are UL listed. ![]() See the IRC for calculating duct length, taking into account duct diameter and bends in the duct. The duct should be secured in place and supported at 12-foot intervals. Or, follow the duct length recommendations specified by the manufacturer (2009-2018 IRC M1502, see Compliance tab). The duct length from the wall to the outlet terminal should be no more than 35 feet, including equivalent length for any fittings. Runs should be horizontal with a slight downward angle if at all possible to allow any condensation from water vapor in the exhaust air to drain. Short, straight, horizontal duct runs are the most effective. Per the requirements of the International Residential Code, Section M1502 (2009-2021 IRC), the clothes dryer exhaust duct should be a rigid or semi-rigid metal duct made of galvanized steel or galvanized aluminum with a smooth interior finish and a duct diameter of 4 inches. The use of PVC pipe for dryer exhaust ducts is also not allowed per all standards and specifications. Not only is a poorly exhausting dryer less efficient, it can also be a fire hazard due to the flammability of the collected lint ( NFPA 2013). These spiral duct designs often trap lint, which can clog the duct, requiring the dryer to work harder and longer to dry clothes and also causing it to increase dryer temperature. Vinyl, nylon, and foil ducts are not recommended and if used will void the warranty of most dryers ( Cranor 2005). Clothes dryers must vent directly to the outside using approved exhaust duct. If this vent empties into a crawlspace, attic, or other building cavity, the potential for moisture-related damage is significant (see the Training tab). Clothes dryers vent about a gallon of water for each typical load of laundry.
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