Condensation – The Silent Home W

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					             Condensation – The Silent Home Wrecker

A certain amount of moisture in the air is essential for comfort, however excess
condensation can cause major problems in a home. Condensation can trigger
structural damage such as rot in window frames as well as damage to your
heating systems and chimneys. It is also responsible for causing mould and
fungal growth on walls and ceilings and in extreme cases if not dealt with, can
damage health.

What exactly is condensation?

All air contains water vapour. The quantity of water vapour contained in the air
depends on the air temperature. Hot air carries much more moisture than cold
air, so as the air temperature rises, it expands and attracts a greater volume of
vapour. Once the air is saturated it hits a dew point and can carry no more
moisture. If the temperature drops at this point, vapour is released.

Condensation Facts

   o   Ireland has the highest humidity in Europe and the West has a higher
       humidity average than the East
   o   Condensation can cause mould and rot damage to your home and chimney
   o   Respiratory problems due to condensation have increased dramatically in
       recent years – due in part to dust mite who only live in moist
       environments and cause Asthma

Where does Water vapour come from?

   o   One shower produces around 1/2 pint of water vapour
   o   Cooking and dish washing produce 1 pint of water vapour per meal
   o   One person’s breathing produces 3 pints of water vapour per day
   o   One house plant produces 1 pint of water vapour per day

Image of house looking saturated.

How does condensation affect my home?

Condensation on the inside of windows has become an increasingly common
problem in newer homes. While old homes were often draughty and expensive to
heat, all that air movement removed excess moisture produced from cooking and
bathing from the house. New homes are tightly sealed so more water vapour
becomes trapped inside the home where it can condense on windows in cold
weather. This can cause serious damage when the water runs down the window,
into the wall and floor.

Reducing the amount of moisture produced in the home is the first defence
against moisture problems. This involves locating the major sources of moisture
and where possible, decreasing their intensity.

Effects of Condensation

The first signs of condensation are usually seen on clothes in a wardrobe, in
particular leather products such as shoes and belts. It could mean that excessive
indoor humidity is causing damage elsewhere such as your walls, ceilings, floors,
chimneybreast or attic. Condensation can even cause blistering and peeling
paint, warping and rotting wood, as well as formation of mildew.

Flues and Chimneys

When chimney or flue problems occur it is important to find out exactly what the
cause is. Our experience at Waterford Stanley is that people spend a lot of time
and money testing various methods, such as fitting cowls, when the problem is
often much simpler to solve.

Condensation can occur all over the house. Poor fuels or a chimney not heating
up fast enough can directly cause condensation in your chimney. Poor fuels
contain too much moisture and are the result of inadequately dried timber or
peat. Without realising the damage created, people load fuel onto a fire and close
off the primary air entry. This of course creates a smouldering effect and deprives
the chimney of air.

During the building stage, a chimney and in particular a chimney serving closed
appliances should be insulated throughout its length. This will help to control
condensation by maintaining a constant temperature. It will also reduce the risk
of plaster cracks on the chimneybreast by preventing too high a heat transfer
from an un-insulated liner.

Gas or Oil Appliances

Appliances of higher efficiency (gas or oil) often have flue gas temperatures that
can be a much as 200ºF cooler than older, less efficient appliances. These lower
flue gas temperatures when introduced into an oversized or masonry chimney will
cause a condition called ‘flue gas condensation’. Liquid appears in the chimney as
a result of burning fossil fuels such as natural gas, propane gas, or fuel oil. It is
easy to blame the new, efficient appliance for the deterioration of a chimney but
it is often the chimney that is unable to manage these increased efficiency levels
due to earlier deterioration.

             How can I control the moisture in my home?

Recommendations for Flues and Chimney

When replacing appliances with higher efficiency models, thought must be given
to chimney design, size and configuration. Many chimneys require relining, which
in effect means installing a new smaller chimney inside the older larger one. This
new chimney lining will reduce the chimney size and create an insulating barrier
between the flue gases and the older chimney, dramatically reducing or
eliminating flue gas condensation.

Check Ventilation and air changes
In older houses a lot of ventilation occurs through fireplace flues and draughty
windows. In modern flats and houses sufficient ventilation does not occur unless
a window or ventilator is open for a reasonable amount of time each day and
while a room is in use. Too much ventilation in cold weather is uncomfortable and
wastes heat so a very slightly opened window or ventilator is sufficient.

How airtight a home is depends on how many air changes take place. The
national average of air change rates for existing homes, is between one and two
per hour, and is dropping due to tighter building practices and stringent building

Try to avoid the use of portable oil or flueless gas heaters if possible. Each litre of
oil used produces the equivalent of about a litre of water vapour. If these heaters
must be used, make sure the room they are in is well ventilated. If condensation
occurs in a room, which has a gas, oil, or solid fuel-heating appliance with a flue,
the heating installation should be checked, as the condensation may have
appeared because of a blocked flue.

Building Regulations
Where heating system appliances are installed, the ventilation and combustion air
requirements must adhere to relevant building regulations. Standard homes built
today usually have air change rates from .5 to 1.0 per hour. Newly constructed
homes can achieve air change rates of .35 or less but most homes with such low
air change rates have some form of mechanical ventilation to bring in fresh
outside air.

Heating to prevent condensation

Ensure all rooms are at least partially heated. The warmer a room is, the lower its
relative humidity. Condensation most often occurs in unheated bedrooms. To
prevent condensation, the heat has to keep room surfaces reasonably warm. It
takes a long time for a cold building structure to warm up, so it is better to have
a small amount of heat for a long time than a lot of heat for a short time.


Insulation is as important as good ventilation at controlling condensation and
humidity inside the home. As outdoor temperatures drop, the surface of the
outside of your home cools and indoor humidity must be lowered to prevent
condensation. The same principle applies to windows. Energy-efficient windows
stay warmer than standard windows and allow higher indoor humidity.

Use a Dehumidifier

Dehumidifiers are effective at removing moisture from the air. Air is drawn into
the unit by a fan, cooled down and excess moisture is safely collected in the
dehumidifier’s removable water container. Excess moisture can aggravate
conditions such as arthritis and rheumatism while recent research indicates that
high humidity causes more house dust-mite activity, which increases the risk of
asthma. So a de-humidifier is a wise investment!


Any sign of mould growth indicates the presence of moisture and if caused by
condensation gives warning that heating, structural insulation, ventilation or all
three may require improvement. Condensation may be a temporary problem in a
new home, however should always be checked out.

This article was brought to you by Waterford Stanley Ltd, proud manufactures of
Cast-Iron Solid fuel, Gas and Oil Cookers and Stoves since 1935. For further
information on controlling your heating system effectively and cost efficiently, log
on to or contact Seamus Brennan or
Jimmy Rushe on 051 302 300.

Irish Energy Website,