| Fogged Thermal Windows |
| Brady Home Inspection Eureka, CA 707 444-9922 |
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Fogged Windows
by Ralph Brady
Thermal windows have two and sometimes three glass panes with a space between
the glass that is typically filled with argon or has a vacuum. A vacuum provides one of
the best forms of thermal insulation, but it is harder to maintain. A properly functioning
thermal window is sealed at the edges and will not allow the gas inside to escape or let
outside air to enter the space between the panes.
Over time the window seal and frame materials can start to deteriorate, due to exposure
to sunlight and air. Also, with changes in temperature the window components (glass,
framing, seals) expand and contract at different rates. This, combined with the
differences in air pressure between the space inside the window and the outside air can
cause the seal between the window panes to fail and leak. The 'failed seal' can now
allow air to move in and out of the space between the windows. This exchange of air is
what results in fogging. Often times if you have a fogged window, it is referred to as
having a failed seal. This does not imply that the window will leak water into the house.
When the seal between the panes of glass has failed, changing air pressure due to
changes in temperature or climate conditions can cause air to be forced out from
between the panes when the pressure is higher inside the window (for example when
the sun is shining on the window, the air between the panes heats up and expands,
creating a higher pressure). As the air cools down it contracts resulting in lower
pressure and outside air enters the space between the window panes. This new air
being drawn into the window cavity has moisture in it. When the window surface cools
down the water vapor in the air can condense on the inside of the window (just like the
on the outside of a glass of ice water). The condensation that forms is water but it also
has salts, minerals and other contaminants which can be left behind when the water
evaporates. This cycle can be repeated multiple times every day. Eventually the salts
and minerals will create a film and powder can even build up near the bottom of the
window. If enough air moves in and out of the space between the windows due to the
leaking seal the condensation can get so bad that water will accumulate and run down
the inside of the window. Between condensation itself and the film left behind from the
salts and minerals, the window can become unsightly and even hard to see through.
Most windows, if properly manufactured and installed, should last 10 to 20 years before
the first signs of fogging begin to show up. It can take years between the time the first
hints of fogging show up and the window becomes unsightly. Larger windows and
windows exposed to direct sunlight are more likely to experience failed seals sooner.
The fogging and condensation is mostly a cosmetic issue. The loss of the vacuum or
argon gas that was originally between the window panes will decrease the thermal
properties of the window, however as long as the seal between the panes is mostly
intact, the double panes will still provide significantly better thermal insulation verses a
single pane window.
Most window frames can be taken apart and a new dual pane assembly installed, which
should be much cheaper than replacing the entire window. However if the windows
frames are worn or if you want to change from aluminum framed to vinyl or wood framed,
then you can change the entire window assembly. Some companies offer a "window a
month" plan, where they just replace one or two windows every month or so to make it
more affordable.
by Ralph Brady
Thermal windows have two and sometimes three glass panes with a space between
the glass that is typically filled with argon or has a vacuum. A vacuum provides one of
the best forms of thermal insulation, but it is harder to maintain. A properly functioning
thermal window is sealed at the edges and will not allow the gas inside to escape or let
outside air to enter the space between the panes.
Over time the window seal and frame materials can start to deteriorate, due to exposure
to sunlight and air. Also, with changes in temperature the window components (glass,
framing, seals) expand and contract at different rates. This, combined with the
differences in air pressure between the space inside the window and the outside air can
cause the seal between the window panes to fail and leak. The 'failed seal' can now
allow air to move in and out of the space between the windows. This exchange of air is
what results in fogging. Often times if you have a fogged window, it is referred to as
having a failed seal. This does not imply that the window will leak water into the house.
When the seal between the panes of glass has failed, changing air pressure due to
changes in temperature or climate conditions can cause air to be forced out from
between the panes when the pressure is higher inside the window (for example when
the sun is shining on the window, the air between the panes heats up and expands,
creating a higher pressure). As the air cools down it contracts resulting in lower
pressure and outside air enters the space between the window panes. This new air
being drawn into the window cavity has moisture in it. When the window surface cools
down the water vapor in the air can condense on the inside of the window (just like the
on the outside of a glass of ice water). The condensation that forms is water but it also
has salts, minerals and other contaminants which can be left behind when the water
evaporates. This cycle can be repeated multiple times every day. Eventually the salts
and minerals will create a film and powder can even build up near the bottom of the
window. If enough air moves in and out of the space between the windows due to the
leaking seal the condensation can get so bad that water will accumulate and run down
the inside of the window. Between condensation itself and the film left behind from the
salts and minerals, the window can become unsightly and even hard to see through.
Most windows, if properly manufactured and installed, should last 10 to 20 years before
the first signs of fogging begin to show up. It can take years between the time the first
hints of fogging show up and the window becomes unsightly. Larger windows and
windows exposed to direct sunlight are more likely to experience failed seals sooner.
The fogging and condensation is mostly a cosmetic issue. The loss of the vacuum or
argon gas that was originally between the window panes will decrease the thermal
properties of the window, however as long as the seal between the panes is mostly
intact, the double panes will still provide significantly better thermal insulation verses a
single pane window.
Most window frames can be taken apart and a new dual pane assembly installed, which
should be much cheaper than replacing the entire window. However if the windows
frames are worn or if you want to change from aluminum framed to vinyl or wood framed,
then you can change the entire window assembly. Some companies offer a "window a
month" plan, where they just replace one or two windows every month or so to make it
more affordable.
| Dual Pane Window Cut-Away View |
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