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Clothes dryer vent totally blocked with water (C) Daniel Friedman Clothes Dryer Lint Trap Safety Warnings
Add-on dryer lint traps may increase the risk of a building fire

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Clothes dryer lint trap safety:

This article describes the fire hazards associated with add-on lint traps installed on clothes dryer exhaust vent ducts. The lint trap that is integral with your clothes dryer should be inspected and cleaned at each dryer cycle - use. Experts advise that you should not use add-on dryer lint traps that can cause blockage in the dryer vent, overheating, and a clothes dryer fire.

This article series describes good practices for clothes dryer vent installation, lint traps, wall vents, filters, and screens. We include a list of clothes dryer fire safety hazards and other clothes dryer installation or maintenance mistakes that are either unsafe or that interfere with effective, economical dryer operation. We discuss types of dryer vent ducting and dryer vent doors or opening protection devices.



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Clothes Dryer Lint Trap Fire & Safety Hazards

Warnings About Auxiliary Lint Filters for Clothes Dryers

Lint Trap

Watch out: Clothes Dryer Lint Traps: like the unit illustrated above and sold a variety of manufacturers and online stores are intended to be installed somewhere between the clothes dryer outlet and the dryer vent outlet - these are are also not recommended in some dryer installation manuals, are prohibited by some building codes, and can similarly cause overheating and fires.

Question: Secondary gas clothes dryer interior lint trap choices

My exterior vent for my gas clothes dryer clogs up with lint on a plastic screen with every load. I rarely bother to go outside and clear it unless I'm gardening in that area.

Can you suggest a better exterior vent? I've seen a 'floating' clothes dryer vent on Amazon. Under pressure from the blowing dryer the plastic lid lifts to expel air and some lint. When the dryer stops blowing, the lid drops shut to keep out insects and small animals. There is no screen. All the reviews are excellent. [1]

I'm also interested in putting in a secondary lint trap, secondary to the one built into the dryer, inside where I can easily open it and clean it out between loads. Several sites say never put a secondary lint trap on a gas clothes dryer because of the danger of combustion fumes escaping inside. Below is a model I found, and when I emailed them they responded that it would be safe.

I have a rigid vent pipe for my dryer exhaust, and there is probably 5 feet of venting between the dryer and the outside portal. Thank you for your time. - Beth Clemensen

Reply:

Clothes dryer safety tips - US CPSC

[Click to enlarge any image]

The clothes dryer safety sketch at left (US CPSC [2]) illustrates a typical clothes dryer installation and outlines a number of fire and safety recommendations. You'll notice that the illustration does not include a secondary lint filter.

The US CPSC reported in 2000 that the lint trap was the second most common source of clothes dryer fires, and that fires in the lint trap, ducts, and dryer vents were responsible for 1/3 of all 79 dryer fires that the study investigated. Interestingly, fires at other locations such as electric motors, thermostats, and wiring may have also been related to clogged ducts and lint traps that led to overheating of those components as well. [3]

We agree that the dryer vent closures you describe offer an attractive alternative for terminating the clothes dryer vent duct line - in cases where there is no secondary lint trap to risk clogging as we make clear below.

But we also agree emphatically with advice from clothes dryer manufacturers that a secondary lint trap on a dryer vent line can lead to dangerous overheating of the system as well as increased dryer time if that device actually traps lint and restricts airflow.

We purchased a dryer vent termination product similar to the ones you describe and examined it carefully as we plan to install it on a Minnesota home where frequent checking of the dryer vent termination outside is inconvenient. The model we examined (not one of those you list) does not call itself a lint trap and it does not appear to trap any lint whatsoever. It's chief advantage is that it blows all dryer exhaust, including lint, into the outdoor air.

Other models such as the Fantech Dryer Booster Lint Trap - Fantech Model DBLT 4 and the Lint Trap by Direct Fans include a removable lint screen that can indeed clog with lint and add restriction to the dryer exhaust air flow - something that the manufacturers do not recommend.

Quoting from the US CPSC:

The U.S. Consumer Product Safety Commission estimates that in 1998, clothes dryers were associated with 15,600 fires, which resulted in 20 deaths and 370 injuries. Fires can occur when lint builds up in the dryer or in the exhaust duct. Lint can block the flow of air, cause excessive heat build-up, and result in a fire in some dryers. [2]

I would stick with the clothes dryer manufacturer's recommendations including their recommendation for metal transition ductwork, cleaning the lint screen at every dryer use cycle, and any prohibition about secondary lint filters.

Your own clothes dryer installation has the significant advantage of a very short run from the dryer to the outside of your home. If you select an outside dryer termination and animal/insect screen that does not trap lint (does not include a lint filter screen) and that opens and closes reliably operated by the dryer vent airflow, that device should be not only in compliance with the manufacturer's recommendations (as it does not include a lint trap screen), it is also (in our OPINION) safer than a vent termination insect or animal screen that becomes clogged with lint.

Follow-Up: what about unsafe blocking of combustion gases from blocked clothes dryer vents

One point, I noticed that in addressing my question about a secondary filter you didn't respond to the point about the possible dangers of blocking combustion gasses inside the house.

Reply: More on CO Carbon monoxide hazards and fire hazards from clothes dryers - carbon monoxide hazards from gas fired clothes dryer

Beth you raise a good safety point that a blocked clothes dryer vent may not only be a fire hazard but might also result in dangerous venting of combustion gases into the building. In particular, if combustion air inflow is blocked because of blocked combustion gas exhaust, the result from a gas fired appliance is likely to be the dangerous production of carbon monoxide.

We have seen that placing a smoke detector or a CO (carbon monoxide) detector too close to a clothes dryer can give off false alarms from at least some detector units, probably because of moist lint and debris becoming airborne. In our OPINION, for safety it makes sense to include a CO detector at a suitable location (not so close as to give false alarms but close enough to protect the building occupants).

It was interesting to note, when reading the clothes dryer fire research articles (cited below) that while some clothes dryers include as a safety feature devices that detect lint blockage, exhaust blockage, and excessive temperatures, those devices have been excluded from clothes dryer safety standards. [3] [4] [5] [6]

We have found references to indoor air quality hazards from un-vented clothes dryers, specifically citing "Produces excessive moisture and dust. Moisture encourages biological pollutants." It is interesting that those authors did not include carbon monoxide from un vented clothes dryers (gas fired) even though in the same article they do cite un-vented gas ranges and ovens as "A source of carbon monoxide and combustion by-products. "

It would be plausible to argue that a vented gas fired clothes dryer whose vent becomes blocked is therefore both a fire hazard and a carbon monoxide hazard. [7]

Readers needing depth in design theory and product recommendations for kitchen and bath ventilation systems should also see our BATH & KITCHEN DESIGN GUIDE and BATHROOM VENTILATION DESIGN and KITCHEN VENTILATION DESIGN or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Clothes Dryer Venting, Insect Pests, & Building Moisture: relationships

See CLOTHES DRYER FIRE RESEARCH

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