| 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.
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.
| Dual Pane Window Cut-Away View |
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.
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.
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