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Fire Hazard Alert - Is Your Dryer Ready to Ignite
In recent years there has been many stories about dryers catching on fire.
Should we be concerned? Yes of course. We should take seriously anything
that may put our family at risk.
Was the problem the dryer? Rarely. After investigating it is usually determined
to have been the venting within the home catching on fire, and not the dryer.
Obviously appliance manufacturers are concerned about the possibility of
any dryer related fires. They have made it a policy to advise both service
companies and consumers that the use of plastic venting is prohibited. They
have also begun issuing cautions not to exceed suggested maximums for venting
length. Let me try to explain the details of this problem.
The drying process
When clothes are being dried inside your family dryer there are two processes
happening. Firstly, heat is applied to the air inside the dryer drum as it
turns. This raises its internal temperature to approximately 175 Fahrenheit
causing moisture to be driven out of the clothes by evaporation. Secondly,
large amounts of air is passed through the clothes. Surprisingly, the real
trick to efficiently dry clothes is not the heat, but rather this vast volume
Ever wonder why the clothes on the clothesline dry so fast on a windy day?
The hero is the wind. Well, the same process takes place inside your family
To make them dry faster air is constantly blown through the clothes during
the drying cycle. The tumbling action of the drum further exposes the clothing
to the hot air flow. While they tumble the air picks up moisture from the
clothes, carries it down the venting, and dumps it outside the home. Most
people think the venting is to push the lint outside. Actually, its primary
purpose is to dump the moisture outside the home.
It is a process that works efficiently. That is, as long as nothing is allowed
to interfere with it. Impede, slow down, or stop the airflow and the process
In the past homeowners who wanted to vent their dryers did it using rigid
sections of venting. The sections were secured together (using screws or
duct tape), and elbows were added if necessary, to connect the dryer and
venting to the wall outlet. Although time consuming to install, straight
venting sections were durable and would often outlive the dryer. This was
in the era when laundry equipment always sat in the basement, against an
Then along came flexible plastic venting. It made installations easier. It
turned an hour installation into a ten minute job. The flex though tended
to become brittle and break easily. Also it was prone to blockage and needed
to be replaced every few years. But since plastic venting was more convenient
we continued with its use.
Then came a change in lifestyle. As both parents went off to work the household
dryer was moved to accommodate our faster paced lifestyle. To save us time
it was moved from the basement to a ground floor laundry room. Although moved
to the working level of the home, it was still close to an outside wall.
So you are saying, I know all this, but what does it have to do with
I answer, Have patience, we are almost there.
Taking this desire for easy access still further the dryer was moved again.
The laundry room is now often located near the centre of the home, close
to the family room or kitchen. If located upstairs it is often centrally
located between the bedrooms, allowing faster access to where most dirty
laundry is produced. Easier for the homeowner that is, but no longer near
an outside wall. The distance from the dryer to an outside wall of the home
is now substantially farther than it used to be.
Presto, we have come to the crux of our problem. The venting is too darned
Physics and the venting pipe
It is a lot more difficult to push air down a long venting pipe than a short
one. This is because air inside the pipe has weight and volume. Obviously,
the air inside a longer pipe would weigh more than a shorter one.
After about twenty feet of venting pipe the dryer begins having difficulty
pushing against all this weight. The average dryer motor does not have enough
strength to overcome the weight of the air inside the pipe. The result is
that the air in the pipe begins to slow down.
Since the air slows down the moisture accumulates in the venting rather than
being carried outside. This causes the venting interior to become wet and
lint traveling through the pipe will cling to this wetness.
This starts a vicious cycle within the venting pipe. It goes something like
this: The more lint in the venting, the more blockage; More blockage means
slower air flow; Slower air flow means more moisture in the venting; More
moisture in the venting means more lint.
I think you understand the scenario now.
Taken to extremes the lint can block the venting closed. When this happens
it can cause the dryer to overheat. The normal drum temperature of 175 Fahrenheit
can quickly shoot up to 300 Fahrenheit or higher. It may even get hot enough
to allow lint in the venting to ignite. If a fire of this type starts within
flexible plastic venting it can quickly burn through the venting and allow
the fire to spread.
Therefore, remove any flexible plastic venting and replace with rigid, straight
sections. If the total length is less than fifteen feet, flexible metal
venting is acceptable.
Calculating true venting length
So lets look at how we can determine if a venting problem is in our future.
Manufacturers generally suggest a venting length of 15 feet (and two elbows)
to be the maximum. But the true venting length can be deceptive.
So how do I know if my venting is too long?
The true length of your venting is determined as follows:
1. Measure all the straight lengths and add them together
2. Count all the turns or elbows and multiply this number by 4
3. Add up the totals
Example Since an elbow or turn is equivalent to an additional 4 feet of pipe
20 feet of venting with 4 turns would actually be:
20 feet + 4X4 feet = 36 feet
Dont be surprised by the true equivalent length of your venting. In
modern homes it can be substantially longer than the manufacturers suggested
If the blockage becomes critical the dryer will stop doing its job properly.
As a homeowner watch for the following signs that the venting may be starting
· Clothes coming out wet
· Excess lint left on clothes at cycle end
· Inside of dryer feels wet
· Taking too long to dry a load
· Clothes very hot at end of cycle
· Electrical consumption greatly increased
So who is to blame for this problem?
I say there is no culprit in this scenario. If you want to blame anything,
blame our fast paced lifestyle. Gone are the times when laundry day was a
full days work. We all want instant gratification and instantaneous results
- even with our laundry chores.
So as a consumer what can you do to alleviate this problem? Well you certainly
can't move the laundry room. The best thing you can do is to be aware that
the problem exists. Consider taking down the venting and cleaning out the
lint buildup during your annual spring cleaning. Also, regularly walk outside
and check the vent cap where it exits your house. Remove any lint buildup
and make sure the flap moves freely. If you see a lot of activity from birds
in you backyard check it immediately. They love to build nests inside the
Other than the previous suggestions a little common sense might avert a tragedy.
Do not operate your dryer while asleep, out of the house, or next door at
the neighbours. And always remember the old saying that states "better safe
About the Author
Copyright 2004 by Donald Grummett - All right reserved.
Donald Grummett is an appliance service manager in Ottawa, Canada. In the
trade over 30 years as both a technician, business owner, and technical trainer.
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