I continually run into confusion from home owners and Realtors regarding what the proper venting material should be for clothes dryers. Statistics from the Consumer Product Safety Commission (CPSC) show that over 24,000 house fires and nearly $100 Million in property damage annually are related to faulty clothes dryer vent installations. House fires related to clothes dryer vents are more common than most people believe but, luckily, are relatively easy to prevent. The photo below illustrates how dirty many dryer ducts are and most people would have no idea until they either (1.) have a fire, or (2.) decide to finally clean out their clothes dryer vent.
During a normal drying cycle, up to a gallon of water may be drawn out of the clothes in the form of water vapor. The purpose of the dryer vent system is to transport this water vapor, and the lint that accompanies it, to a safe location outside the home. The most commonly seen improper type of dryer vent is flexible vinyl tubing. Vinyl is a type of plastic and it can easily melt and lead to a house fire. This material, most often white and ribbed, tends to allow for lint to readily accumulate inside of it. Lint is very flammable and all it takes is a small spark to ignite it leading to a house fire. The more lint that fills a clothes dryer vent, the more energy the clothes dryer consumes to try to dry the clothes as air won’t freely flow through the clogged vent material. This, in turn, causes the drying cycle to be much longer (possibly hours more) than normal and raises utility bills. The photo below shows vinyl tubing.
Another improper dryer vent material that I routinely see installed is mylar foil tubing (see photo below). It is a flexible ribbed shiny tubing that many home owners and contractors have installed and they wrongly assume that it is metal because it is shiny. Mylar foil tubing is not approved for use as a clothes dryer vent material and should not be used for this application. The photo below shows an installation of mylar foil tubing which actually runs behind a fixed wall covering. A few manufacturers of mylar foil tubing have been able to obtain a UL listing (UL 2158A); these products specifically should be used as the transition duct ONLY between the dryer and the actual rigid metal dryer vent (not the full dryer vent!). If the mylar transition duct is UL approved, it will have a UL sticker on it stating "UL 2158A". If it has no sticker, then it should be assumed it is not UL listed and should be replaced with a proper rigid metal dryer vent material. The transition duct should be as short as possible to connect the dryer to the metal vent (no longer than 8'). The transition duct must not run within a wall, floor, or ceiling covering since it will not be able to be visually inspected and can't easily be cleaned.
Mylar tubing may melt leading to a house fire
I also occasionally find mylar tubing venting a clothes dryer into the basement with a plastic container (see photo below). First, the tubing is incorrect if it is installed for more than 8'. Second, venting the clothes dryer into the basement takes the moisture out of the clothes that the dryer is drying and discharges that back into the home. This creates an environment that is a fire-hazard (lint) and a mold-hazard (moisture). This type of vent also tends to get crumpled and therefore blocked. I've also seen the below pictured installation discharging into a garage; the same above hazards pertain but, with the vent terminating in a garage, carbon monoxide or a garage fire can readily enter the home via the vent.
In the above photo, this seller has their dryer vent discharging into the basement (likely leading to excessive basement moisture or mold) plus the gas-fired water heater's combustion air intake and burner are within 2' of the dryer vent termination. The excessive moisture can allow for corrosion of the gas burner plus, since lint is flammable, it also presents a fire hazard.
Something that I’ve been running across more often lately in homes built within the past 20 years is some builders installing 4” PVC drain pipe as the clothes dryer duct. At one recent home inspection, I even found black corrugated plastic drain pipe (normally used to run an exterior downspout away from the home) being used as the home’s dryer vent. While PVC is meant for plumbing and venting applications, PVC is not approved for venting a clothes dryer and should not be used for this application. PVC pipe is plastic and can allow a static charge to build up; this static charge can ignite dryer lint leading to a fire. The photo below from a recent home inspection shows vinyl tubing (left side) connected to PVC pipe (right side) with cloth duct tape. All 3 items are wrong (the vinyl tubing, the duct tape, and the PVC pipe). Whoever installed this is batting 0-for-3.
The IRC (International Residential Code) section M1501 requires that clothes dryer vents be constructed of at least 0.016" thick rigid metal, have smooth interior surfaces, and shall not have sheet metal screws extending into the duct. The clothes dryer vent should meet the UL 2158A standard. Sheet metal screws penetrating into the material allow lint to get caught on the screws and possibly clog the vent over time (see the 2nd photo below). Keep in mind, that a home inspection is not a code compliance inspection and that the AHJ (authority having jurisdiction) is the responsible party for determining/verifying code compliance. The home inspector is using these standards, however, as a reference to help protect his client from possible future hazards, such as a house fire. The first photo below shows the proper rigid metal duct material. Notice how this rigid metal duct looks nothing like the mylar foil material. This material can't easily be bent.
These photos show rigid metal dryer vent. The vent pieces should only be secured to each other with
foil tape, never use screws. Using screws (seen in the bottom photo) will allow lint to easily clog the vent's interior.
Dryer ventilation systems should only terminate to the home’s exterior and have a proper dampered exterior cover to help prevent water, birds, insects, etc. from entering the duct. The exterior cover should not have a screen since it will cause lint build up and block the vent over time. Venting a clothes dryer into a garage, basement, attic, or anywhere else inside the home can lead to excessively high humidity levels, mold, as well as an increased fire risk. Also, a clothes dryer ventilation line should terminate to an area of the home’s exterior where it can not be blocked by vegetation, snow, dirt, etc. and be at least 3 feet from doors and windows. The vent also should not terminate near an air conditioning compressor as the dryer lint can accumulate on the A/C compressor which can prevent proper operation of the A/C system. If your area receives a high amount of snow, also ensure that the dryer vent termination point is kept free of snow, otherwise, the risk of fire or carbon monoxide accumulation is increased.
Screens should not be used as they catch lint and will block the dryer vent.
The dryer vent's exterior termination should have only a louvered or dampered cover.
Clothes dryer vents should not discharge into attics. This puts a considerable amount of lint (flammable) and moisture (can lead to mold) into the attic.
Flexible rigid metal ducting (this specific material is only slightly bendable) is recommended where the rigid metal duct material connects to the clothes dryer. The photo below shows flexible rigid metal ducting. Notice how different this rigid metal material below looks compared to the mylar foil ducting shown in the 3rd photo from the top of this article. If the clothes dryer and exterior vent are in close proximity, a single piece of flexible rigid metal duct (as seen below) can often be safely used as the sole duct, assuming it does not pass behind a wall, floor, or ceiling covering.
I also sometimes find dryer vents that far exceed 40 feet in length. In this case, I recommend that the vent system be modified to terminate to an alternate exterior location closer to the laundry appliances to allow a shorter run. Most standards call for clothes dryer vents to be no more than 25 feet in length, have few bends, and no kinks. Gas dryers, though, are permitted to have vents up to 35 feet in length. The more bends in the vent that exist, the shorter the overall length should be. For every 90 degree bend, the vent should be shortened by 5 feet; for every 45 degree bend, the vent should be shortened by 2.5 feet. An exception exists if the clothes dryer’s manufacturer specifically permits a longer vent but, in most cases, the inspector does not have this documentation from the clothes dryer’s manufacturer.
As part of a home inspection, the inspector should report whether the clothes dryer vent is visible, its apparent condition, and recommend modification if the vent terminates in an improper location. If the vent is not visible (such as passing through walls/ceilings or insulation), the home buyer should verify that a proper rigid metal vent is installed and find out from the seller when it was last cleaned.
With every home inspection, I always recommend that the clothes dryer vent system be thoroughly cleaned at least twice per year as preventative maintenance. In most cases, the home owner can take apart and clean the dryer vent’s interior; this is made easier with a vacuum cleaner with a long hose attachment. Some HVAC professionals and chimney sweeps also offer dryer vent cleaning as a service and there are a few companies that specifically clean clothes dryer vents as their main business.
During a home inspection, the inspector will try to determine the type of clothes dryer vent material(s) installed. In some homes, only part of the clothes dryer vent system may be visible. Often, socks or other clothing have fallen behind the laundry appliances against the wall and these items can block sight of the dryer vent where it passes into a wall or floor. Installed insulation, ceilings, or walls as well as other nearby stored items can block visual access to the dryer vent material. Of course, home inspectors do not move insulation, disassemble walls/ceilings, or move appliances to perform the inspection so visual or physical access to the dryer vent is sometimes limited.
House fires related to improper or blocked dryer vents are easily prevented and a little bit of preventive maintenance can help save lives. When was the last time you inspected and cleaned your clothes dryer vent? Your family's safety may depend on it.
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© 2015 Matthew Steger
Matthew Steger, owner/inspector of WIN Home Inspection, is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), an electrical engineer, and a US Dept. of Energy Home Energy Score Assessor. He can be reached at: 717-361-9467 or firstname.lastname@example.org.
WIN Home Inspection has provided a wide array of home inspection services in the Lancaster, PA area since 2002. This article was authored by Matthew Steger, ACI - owner of WIN Home Inspection in Lancaster, PA. No article, or portion thereof, may be reproduced or copied without prior written consent of Matthew Steger.