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Basics
Unheated storage areas
How does a dehumidifier work?
There are four types of dehumidifier sold to the
domestic market in the UK - Compressor (the majority), desiccant,
peltier and silica gel.
A compressor based dehumidifier draws the air in from the room over
a filter and passes it over some cold coils similar to the coils on
a fridge. As the coils
are cold, water condenses and drips into a bucket.
The air is then reheated to room temperature and blown back out
of the dehumidifier.
A desiccant dehumidifier has no coils and
uses a wheel filled with a moisture absorbing desiccant material to
extract the water from the air. The air is then reheated to about
10°C above room temperature and is then blown back into the room.
A peltier dehumidifier basically uses a cold metal
surface to condensate the air on. These should not be used below
15°C and will not control much more than a large wardrobe.
A silica gel based dehumidifier normally comes in a
tub or a rechargeable cassette and should not be used to control more
than a box/draw or wardrobe.
Why does water appear on my windows/cupboards/walls?
It is a basic law of physics that if the surface
is cold enough and if there is enough water vapour in the air then it
will condense. This means
in the case of windows whether they are double-glazed or not that if
the windows are cold enough and there is enough moisture in the air
then condensation will occur.
Where does this water come from?
We all produce water by drying clothes indoors, the boiling of
vegetables, showering, rain, calor gas heating and making cups of tea
all produces moisture. It
is just an on-going process that never stops.
Can I just get rid of it by opening my windows?
This is fine on a nice summers day but in winter
opening your windows will just result in you losing the heat from your
central heating and creating draughts.
This is a waste of money and if it is raining will just let more
moisture in. You might
as well just throw fivers out of the window.
Will a dehumidifier do the whole house?
A dehumidifier creates a volume of dry air in as
large a space as its fan can effect.
After that it will be helped by the fact that damp air will always
migrate to dry places. As
long as you leave all of the internal doors open a correctly sized dehumidifier
will prevent condensation and mould from appearing around the whole house.
What about the black spots of mould on my window
and bathroom sealant?
Mould occurs around 68% humidity, condensation occurs
at 100%. As you can see
from this you can have mould but still have clear windows.
A dehumidifier will prevent the mould from getting any worse
and once you have cleaned the mould away, it will stop it from coming
back.
Do I put it in the worst room?
You can if you like put it in the main problem area
to start with and then move it somewhere more convenient when you feel
that the problem is under control.
If it is just condensation on the windows that you are worried
about a dehumidifier in a central position, at for example the bottom
of the stairs, will cure the problem in the whole house.
Are they expensive to run?
A compressor based dehumidifier costs about 2-3p an hour to run.
You should take into consideration the fact that the dehumidifier
will not run all the time, as it will be controlled via its humidistat.
Secondly it is very expensive to heat a damp house and you will
see a reduction in your central heating bill when you start to use your
dehumidifier.
What is the humidistat?
Just as you have a thermostat that you set on your
central heating you have a humidistat on your dehumidifier. This will allow the dehumidifier to turn off and on as required
without you having to worry about it.
Should I turn the dehumidifier on for just a few
hours a day?
No just let the dehumidifier decide when to come
on using its humidistat.
Will they help with allergies?
A dehumidifier will reduce the relative humidity
in the house, which will prevent dust mites and other pests from breeding.
In this way a dehumidifier can help with allergies.
For more information on allergies and fighting dust mites please click
here.
Unheated
areas
Why do unheated areas get separated out?
A dehumidifier that can be found in your local high
street store is designed for use in your home, which is nice and warm.
In a garage, store, workshop, boat, caravan, holiday home or
a conservatory the temperature will drop a lot lower.
Since a compressor based dehumidifier works by reducing the temperature internally
it can easily reduce down to freezing even if the ambient temperature
is 10°C. What you do not
want is for your dehumidifier to form a block of ice or for you to find
a puddle on the floor.
What happens when the temperature in the room
drops down towards freezing?
Most dehumidifiers designed for use in the home will
just stop working and turn themselves off.
Others will try to work and might well suffer from a build up
of ice. Those with a defrost
system are likely to only extract a tiny amount of water.
What is the correct type of dehumidifier to use
in these applications?
You need a machine with a function called hot gas
defrost or a desiccant based machine. If the dehumidifier
does not have either of these features then do not buy it. Examples of our
current range can be found here.
How does Hot Gas Defrost work?
Hot gas defrost works by reversing the coils and
using the heat from the hot side of the coils to melt the ice to water.
When this is done the heat is returned to the front of the machine
to warm the air before it is blown back out.
So what temperature will a hot gas defrost system
or a desiccant dehumidifier work down to?
Freezing.
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