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 of air.
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 dryer.
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 quickly fails.
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 outside
wall.
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 venting fires”.
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 long.
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
Don’t be surprised by the true equivalent length of your
venting. In modern homes it can be substantially longer than
the manufacturers suggested maximum.
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 to block.
·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
Summing up
“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 simply love to build
nests inside the vent cap.
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
than sorry".
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. For more information about appliances including FAQ, Stain guide, Recycling, and Newsletter visit http://www.mgservices.ca