All gas clothes dryers have vents to expel the combustion gasses create by the gas burners of the dryer. If a gas dryer vent becomes clogged with lint or other debris, the dryer ceases to move air efficiently, causing unnecessarily long drying times and a resulting waste of energy. A clogged dryer vent can even become a fire hazard, too, when highly combustible lint backs up into the area where the burner could ignite it.
Another problem is that a clogged vent can cause heat to build up in the dryer, which is likely to blow a protective device called a thermal fuse. If this happens, the dryer won’t heat at all and, in some cases, won’t even tumble.
What causes a dryer vent to become clogged with lint? The problem is usually rooted in the length and nature of the run from the dryer to where the vent exits the wall. If a dryer vent is too long or circuitous, moisture in the warm air passing through it condenses on the vent surfaces, attracting lint. Eventually, the lint builds up and a forms a paste, creating resistance. A sure sign of this problem is unusually long drying times or, worse, a dryer vent that collects or drips moisture.
The best dryer duct material is rigid, non-ribbed metal ductwork. Do not use plastic ribbed duct material—it is a fire hazard. And avoid smooth plastic ducting, too—even a few feet of this will extend the drying time for every load of clothes you do. A 4-inch-diameter metal duct is best. Anything smaller is too constricting and anything larger is too voluminous to allow air to be pushed through with some force.
The shorter, straighter, and more level (or downward) a dryer vent’s run to where it exits the house, the better. It’s ideal to place a dryer on an exterior wall where it can vent directly outdoors. The goal is for the vent to have as little resistance and as few places for lint to accumulate as possible. Bends, elbows, turns, and dips will catch lint as it passes by. Screws at duct joints cause the same problem—for this reason, make all connections with aluminum foil tape. By keeping resistance and lint catchers to a minimum, you can extend the life of your dryer and save money by shortening the time needed for drying.
How far can you reasonably run a dryer duct? This is a common question because dryers sometimes must be located a distance from an exterior wall. The answer to this depends on a number of factors, including the size of the duct, the duct material, the number of elbows in the line, and the size of the vent hood that is mounted on the wall where the duct exits. If distance is a concern, definitely use rigid 4-inch-diameter sheet-metal ductwork.
Distance standards are set both nationally and locally; local standards are sometimes different than national ones, but you’re usually better off abiding by the more rigorous codes because they are more likely to ensure good dryer performance. Typically, national codes set a maximum of 14 feet as the allowed length for a solid sheet-metal vent that has two 90-degree elbows (after the elbow at the dryer). Subtract 2 feet for every additional elbow. Local codes may allow 25 feet for a run with two elbows but subtract 8 feet for each additional elbow.
If these numbers are longer than your dryer’s duct run, you have two choices: 1) Reroute the duct to a nearer exit point or 2) attach a dryer vent booster fan to the line. If the first choice is an option, you’ll need to cut-in a new vent hood, patch the old one, and reroute the ductwork. The second choice, a dryer booster fan, is a small inline fan that is installed at least 15 feet from the dryer, where damp lint cannot be lodged in it. These fans are turned on and off by a pressure-sensitive switch that senses air movement in the vent.
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