Windows do not cause condensation.
Excess interior humidity is the source.
Everything you need to know about condensation.
A little fog on the corners of your glass
shouldn’t bother you. And it probably doesn’t. But “problem” condensation, fog or frost
that covers whole windows, definitely bothers you. And it should. The visible effects are just the tip of the
iceberg. What is happening elsewhere in your home? Take your attic. Excess moisture may be
freezing in the insulation where it will later melt and damage your plaster. Or perhaps it’s forcing its way out
through your siding, where it will form blisters under the exterior, or it may be promoting mildew in your home.
The culprit is too much water vapor.
Not the window, not the insulation, not the paint. The only answer is to get rid of excess water vapor. Water
vapor, or humidity, is one of the invisible components of air. This humidity tries to flow toward drier air, since
this air has a lower vapor pressure. In other words, the higher vapor pressure in moister air forces the moisture to
areas which are drier.
In cold weather, the air outside is generally drier than within a warm house. What happens, then, is that the moisture
is forced to the outdoors. The most obvious indication of this is condensation on your windows: the moisture comes
in contact with the cold surface of the glass. It therefore condenses to form either frost or water (depending on whether
the temperature of the glass surface is below or above 32°.
construction of modern homes traps the moisture in many ways. Certain varnishes, tiles, plastics and acrylics—which
are increasingly used in construction—do not allow moisture penetration. Thus the moisture created by kitchens,
laundries, bathing and human bodies (as well as cat, dog and other pet bodies) can’t flow easily to the outside.
Insulation and construction materials that are designed to keep cold air outside also keep moisture inside, further increasing
the moisture level in your home.
Forced hot air system return vents, especially located
on the floor below a window, will draw warm, moist air across the interior surface of the window glass. Condensation
may occur if this air is too humid and the glass temperature is cool enough to create a dew point. Condensation
can occur on any window in any room, even rooms where several other windows are installed and they remain unaffected. Reduce
the occurrence of condensation by:
- Diverting the return air to a different register away from the window
- Close off the return, thereby shifting the return air to a different register
- Install a dehumidifier in the suspect room
- Turn off or lower the humidistat on your furnace
A room can actually have a "convection current", whereby warm air rising out of
the heating device below the window crosses the window above. This window amy be cool enough to chill the air which then causes
the cooled air to drop. As the air is heated again and rises, it again crosses the plane of the window where it again is cooled
and drops downward. This"draft" is not a "draft, it is physics. Warm air rises, cool air drops.
Divert the warm air register to keep warm, moist air from directly
or indirectly striking the inside glass surface. Warm air holds more moisture than cold air.
A single vent pointed at a window may cause condensation to occur on that window without affecting other windows in
the same room.
Order windows with
the Super-Plus+E or the Premium Plus+E Home
Comfort Energy Packages and what happens: the glass is warmer in the wintertime, cooler in the summer. By raising the glass temperature,
the dew point is changed. There is an upfront cost up for either glass package, but the rewards are many.
Less fuel use, less risk of conductive draft and a reduction in the risk of condensation occurring on the glass.
In simplest terms, condensation
is simply moisture build-up on a material that is below the dew point temperature of the surrounding air. If the glass goes
below that temp - you have condensation. If it doesn't then you don't.
- Clearing the Air About Condensation, Tom Feiza, Home Tips
- Home Moisture, Home Energy Guide, Minnesota Department of Commerce
Energy Information Center
- Indoor Air Quality – Temperature and Humidity, Environmental Health & Safety, Bowling Green State
Notes on Moisture Control, University of Illinois Small Homes Council, Building Research Council
How to further decrease the chance of condensation occurring on the interior
of your window
Ask for ENERGY STAR!
Star rated energy efficient windows will further cut down the creation of moisture on the glass by raising the interior
glass surface temperature in wintertime. However, if a home continues to have excess
humidity, new windows will not eliminate the humidity; only diminish the possibility of condensation occurring on the glass.
ENERGY STAR qualified windows, doors, and skylights save you energy and money, increase
the comfort of your home, and protect your valuable possessions from sun damage. They are also better for the environment
because lowering your energy use means less air pollution from power plants.
Save money and energy. Replacing single-paned windows with ENERGY STAR qualified windows or
choosing ENERGY STAR over the typical clear-glass double-paned alternative can save a significant amount of money on your
goodbye to winter drafts,reduce the risk of sweating and lower the inside temperature of the glass in the summer sun.
Thanks to a host of new technologies including Super Spacer, ENERGY STAR qualified
windows, doors, and skylights keep your home cooler in the summer and warmer in the winter, making you more comfortable year round.
Protect your home's interior. Many ENERGY STAR qualified windows, doors, and skylights
act like sunscreen for your house, protecting your photographs, artwork, furniture,
carpets, and wood floors from sun damage.
with confidence. Every ENERGY STAR qualified window, door, and skylight is independently
certified to perform at levels that meet or exceed strict energy efficiency
guidelines set by the U.S. Department of Energy.
Ask for ENERGY STAR. To purchase the most efficient window for your home, ask for products
that are ENERGY STAR qualified in your Climate Zone. To learn more, see the window purchasing
tips on the following website:www.energystar.gov.
and insulate with Home Sealing. Sealing your home's envelope is one of the
most cost-effective ways to lower your home's energy bills and improve your comfort.
What's in a pane - or two - or
All energy efficient windows have at least two panes, but
not all double-paned windows are energy efficient. Twenty years ago, double-paned meant energy efficient; today, advanced
technologies have enabled the development of triple glazed windows that are much more efficient than traditional clear-glass
double-paned windows. For maximum energy savings, count on ENERGY STAR.