Q–I just discovered that the clothes dryer exhaust in my new home dumps into the attic near a roof vent. There is a large collection of lint in the attic. The builder claims that this is perfectly acceptable. Is he correct?
Is the solid vent piping better than flexible piping? Can you vent a dryer through a roof or a soffit with minimal problems? What about those interior vent kits that claim energy savings? Is that a good option for me?
A–I see inferior dryer vent installations like yours on a monthly basis. Dryers that exhaust into garages and crawl spaces are also potential problems.
Ask your builder if your local building inspector finds his installation “acceptable.” Virtually every model building code addresses clothes dryer exhausting. The codes mandate that dryer exhaust needs to be ducted outdoors. Terminating the exhaust pipe near an attic vent does not meet this requirement, plain and simple.
Clothes dryer exhaust can cause major problems within a house. In your case, there are two imminent hazards. One is a fire hazard from the massive quantities of exposed fabric lint. An open flame could turn your attic into an inferno within seconds. I also suspect that you will have mildew growing up there in short order from the large amount of humid air that the dryer dumps into the attic with each load of laundry.
Interior vent kits do not meet most model building codes and they inject vast quantities of humid air into a home. Condensation on windows, within exterior walls and in attics can result from this method of dryer venting. This trapped moisture can cause wood rot and mildew problems.
Dryer venting is not as simple as it seems. The blower motor within a dryer can push the moist air only so far. If you exceed this limit, the dryer will not dry clothes properly and the vent piping can easily clog with lint. The exhaust hood design, the type of exhaust pipe used (smooth metal vent versus corrugated/flexible metal pipe) and the number of bends in the exhaust piping all affect the ease with which the air flows from your dryer.
Smooth metal vent pipe and exterior exhaust hoods that have openings of 16 square inches or more offer the least resistance to air flow. If there are no bends or turns in the exhaust piping, the dryer can be placed up to 64 feet away from the exhaust hood. The addition of four 90-degree bends reduces the permissible length of straight pipe to 27 feet between the dryer, the bends and the exhaust hood.
Exhaust hoods with narrow mouths often have only 10- to 12-square-inch openings. If you use one of these hoods with flexible piping with four bends in it, you can only have 15 feet of straight piping between the bends, dryer and exhaust hood.
A dryer can be vented through a roof if you use the correct exhaust hood. The best hoods are one piece and contain wide flanges that permit a leak-proof installation under common asphalt shingles.
The hoods include insect screening and a built-in damper that stops outside air, bumble bees or other pests from blowing or flying back into your dryer.
Venting dryers through soffits is not a good idea. Humid air can often find its way into your attic through soffit vents.
Because you live in a cold climate, you need to make sure your builder insulates the metal dryer pipe when he connects it to the new special roof exhaust hood. Without this insulation, the metal pipe will chill the moist air within the pipe and create condensation. This moisture will run down the pipe and possibly leak from the pipe joints or show up as a leak under your dryer. High-quality, reinforced foil duct tape–found at heating and cooling supply houses–is the best material to use to secure the insulation to the metal piping and the insulation backing. Standard duct tape can fail in the extreme temperatures found in many attic spaces.
Check to see how your dryer vent pipe was fastened together. If your builder used screws as fasteners, it was a mistake. The screw shafts inside the piping collect lint and cause additional friction. Manufacturers and building code enforcement officials prefer that the pipes be joined with reinforced foil duct tape, in conjunction with special, large-diameter clamps that squeeze the pipes together.
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Have questions about the remodeling process? Write to Tim Carter, c/o The Chicago Tribune, P.O. Box 36352, Cincinnati, Ohio 45236-0352. Questions will be answered only in the column.
For more information on duct lengths, duct bends, exhaust hoods, roof hood manufacturers and other tips on installing dryer vents, send $2 and your name and address to Tim Carter at the above address. Ask for Builder Bulletin No. 223.
