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Venting About Dryers

There is more to know about cleaning laundry than separating whites and colors. While it is easy to overlook what goes on behind the scenes, a ‘hands off’ approach to laundry functions can lead to higher operating costs and safety concerns.

Dryer exhaust systems function to remove irritating and potentially harmful moisture, odors, and exhaust gases. A typical residential dryer can remove up to one gallon of water from a single load of laundry. Without exhaust systems, high concentrations of moisture in laundry rooms would promote mold and mildew growth, leading to health and possibly structural problems.

“Signs of dryer exhaust problems include longer-than-normal drying times, linens coming out exceptionally hot, and the dryer feeling hotter than normal.”

A good laundry system starts with a collaborative design process involving the facility owners, the architects, and the engineers. One critical planning aspect for both new and replacement installations is a dryer’s physical location. Code listed limitations on maximum dryer exhaust duct length can seriously impact practical dryer location options. Typical code requirements state that dryer exhaust ducts be no longer than 25 feet, minus allowances for duct bends. Fortunately, there is a code exception that allows for greater duct lengths when listed by the dryer manufacturer and when approved by a local code official. This exception provides the opportunity for greater flexibility within most floor plans.

Occasionally, circumstances do not allow for a dryer to be installed and still meet code and manufacturer duct length requirements. Increasing the duct size is generally not an option because dryer manufacturers’ performance data and listings are established with 4” round ductwork. Using larger ductwork will normally void the manufacturer’s warranty and would require approval by a local code official. One possible solution, however, is to incorporate a dryer booster fan into the exhaust duct. While most booster fans are UL listed for this application, dryer manufacturers have not explicitly tested their dryers with booster fans. Consequently, using such a fan requires special approval from the manufacturer.

Neglecting to maintain dryer exhaust systems can be just as detrimental as poor design and installation. Over time, any dryer exhaust system will suffer from the abuse of exposure to extreme moisture, heat, and lint. Lint build-up containing high levels of moisture can pose problems including premature duct corrosion. Once dried out, accumulated lint poses an even greater threat as a potential fire hazard. Studies published by the U.S. Fire Administration indicate that failure to clean dryer exhaust systems is the primary cause of laundry fires. Signs of dryer exhaust problems include longer-than-normal drying times, linens coming out exceptionally hot, and the dryer feeling hotter than normal. Implementing a preventative maintenance program and providing adequate maintenance access around dryers, fans, and duct clean-outs for system inspection is essential to successful operation.

Properly designed and maintained clothes dryer venting systems are a wise use of resources. Operating savings of 10-30% over poorly maintained systems can be expected. Other benefits include less strain on equipment, less energy waste, and shorter drying times.

– Samuel M. Snyder, PE, LEED AP

Sam is a Licensed Mechanical Engineer and LEED Accredited Professional. Please feel free to contact Sam for further details regarding the above information.