Condensation

Facts about Condensation and what can be done about it.

To provide you with some helpful information regarding condensation listed below are several articles from different manufacturers on the subject.

Article produced by Marvin Windows & Doors(7/10/2000): Humidity is water vapor mixed with air. It is invisible. Condensation is fundmentally humidity made visible. Condensation can be compared to rain. Before rain is formed into droplets it too is water vapor. When it condenses it becomes rain and falls to the earth. When humidity condenses, on windows for instance, it becomes what we call condensation.
Often you will hear humidity referred to as indoor relative humidity. What is it? Air can hold only a limited amount of water vapor, and that abount depends on the air temperature. When air at a certain temperature contains all the vapor it can hold, it is said to have a relative humidity of 100 percent. Thus, when it holds only half of the water vapor it can hold, the relative humidity is 50 percent.
Cooler air is capable of holding less vapor than warmer air. During the winter, as cold dry air enters a house, and warm moist air leaves it, much of the moisture produced through normal household activities is allowed to escape from the home. This exchange of air keeps the relative humidity in the home at acceptable levels.
This is why old, less energy efficient homes which allow more air infiltration are not particularly bothered by moisture buildup.
When the cost of heating began to rise, people became more aware of energy saving techniques, and began caulking, weatherstripping, insulating, and replacing ineffective windows and doors. The result was a substantial reduction in air infultration causing a rise in interior relative humidity. This humidity then became apparent as moisture condensation on windows, walls, and ceilings.
Unfortunately, windows are usually the first place that excess moisture in the home becomes apparent. The temperature of the glass in the window and the air next to it is substantially lower than the temperature of the rest of the home. The relative humidity near the area of the glass will increase as the temperature decreases. When the relative humidity in this area exceeds 100 percent, the moisture in the air condenses on the glass. The same effect can be obtained on a cold water faucet. Open a cold water faucet in your home and allow the water to run for a few minutes. As the water runs, the temperature of the faucet will drop. Within those few minutes the water temperature should be low enough to produce condensation. Condensation on the glas surface of your windows is an indication that the home contains excess moisture.
HOW DOES MOISTURE GET INTO YOUR HOME?
Possible origins of moisture in your home include: cooking, cleaining, bathing, washing clothes and dishes, drying clothes, breathing and perspiring.
HOW CAN YOU CONTROL MOISTURE IN YOUR HOME.
Ventilation is the most effective means for you to remove moisture. Be doing this you will exchange some drier, cooler outside are for warm humid interior air and your moisture levels will be reduced. He are some simple solutions for reducing moisture:
1.) Use a kitchen fan while cooking (it must be vented to reduce moisture)
2.) While showering, keep the bathroom door shut and have an exhaust fan running.
3.) Your clothes dryer must be vented outside.Also do not hang clothes up to dry inside your home during cold weather.
4.) Shut off all humidifying devices.
5.) If you have a fireplace, open the damper occasionally to allow moisture to escape.
6.) All air to circulate. Do not cover hot or cold registers. Leave drapes open to allow air to circulate freely over windows.
7.) Keep all rooms at a minimum of 10 degrees C(50 degrees F) even if unoccupied because condensation will occur in an unheated room.
8.) Run exhaust fans while washing floors because washing floors adds large amounts of moisture to the air.
9.) If you do not have a fresh air intake into the cold air return duct of your heating system, have one installed. Make sure that the intake damper is open and that there are no obstructions to prevent air flow.
10.) Attic ventilation can be provided with inlet vents, along the eaves, and outlet vents, along the ridge and gable ends. Eave vents must not be blocked by ceiling insulation, and ridge vents must not be blocked by snow. Warm air escapes through the ridge vents and cool air enters at the eaves.

Article by Milgard Windows:

COOL AIR JUST CAN'T HANDLE IT. Most of us keep our homes (together with all this moisture) at a warm, comfortable temperature. But when the warm, moist air comes into contact with a cooler surface, this moisture condenses - whether it's on a glass of ice water, a mirror - or a window.The fact is cool air can't hold as much moisture as warm air can. So the moist air around a cool surface will simply turn into tiny water droplets. It's important to understand these surfaces are not - sweating - moisture into the air. The condensation is the result of invisible moisture, or water vapors already in your home. Moisture that builds up between the panes of glass is not condensation - it's a failed insulating unit - and should be fixed immediately. Most companies guarantee their insulated unit for a period of time so check your warranty carefully.

NEW OR OLD, YOUR HOME IS AT RISK: Most older homes were built to be less weather tight than those built today. As a result, they have better ventilation, and water vapor flows more easily through the walls. This actually helps cure some of the problems associated with moisture. However, these same older homes typically have single-glazed windows - which result in cold glass surfaces that cause condensation when ever small amounts of moisture are present. Meanwhole, today's newer homes usually have better performing windows with double-pane insulating glass. The resulting warmer glass surface allows a greater amount of moisture in the home before it condenses. But iodays homes are built so - tight - moisture will continue to build up in the home unless adequate mechanical ventilation is installed. What's worse, this moisture will try to permeate the drywall and insulation in your walls to equalize with outdoor humidity levels. When between the walls, the water vapor cools and condenses, causing potential damage to the structure of your home.

EXTERIOR CONDENSATION: Condensation can also appear on outside surfaces when a higher performing glass type (ie - LowE) is used. This glass can allow the outside surface to reach the dewpoint because it reflects the heat back indoors and off the glass surface. As outside air temperature increases, the outdoor condensation should diminish. You will mainly see this challenge in the morning hours. This is the same phenomenon that is observed on your lawn, outdoor furnishings, or your car windows when left out for the evening.

THE WEATHER INSIDE YOUR HOME: Condensation on the windows of a home has long been a problem of homeowners in all types of climates. Whether you live in the sunny desert of the Southwest or the damp woods of the Pacific Northwest, you're not immune to its effects. That's because the "climate" inside your home has less to do with the weather outside. Fortunately, however, it;s a climate you can control. Chances are you've been annoyed by condensation in the past. But condensation is not only annoying - it's an indication of excess humidity in the home which can cause peeling paint, rotting wood, and damage to the window sill and sheet rock around the window. This moisture can even result in health problems like allergies from molds and mildew. Today's energy efficient windows help fight condensation better that ever, but dependig on your lifestyle, even the best windows will show some signs of condensation. That's because the real problem isn't a window problem - it's a moisture problem.

AIR AND WATER DO MIX: There's a lot of moisture - or humidity in the air inside your home. Your everyday household activities will make sure of that. Things like taking showers, cooking, houseplants, poor ventilation - even breathing - account for most of the moisture in a home. Even the lumber in your new home consists of about 15 - 20% moisture. Consider the fact that just the normal perspiration and breathing of a family of four adds nearly two gallows of water to the air each day. Combined with the normal daily activities of your family (like cleaning laundry and showering) and you'll add over 18 gallons of water a week to the air in your home. That's about two aquariums full floating through the air of your home.

START BY FIXING THE SOURCE OF THE PROBLEM: The first step in reducing excess moisture is to make sure you home is well ventilated. Changing moist indoor air for drier outdoor air will help cut down on indoor humidity dramatically. So for starters, open a few windows or turn on a bathroom fan during or after a shower. If your home is brand new, make sure to open a window on dry days to let the damp lumber dry out a bit. Also make sure your gas burners and clothes dryer are vented to the outdoors. You could also choose to structurally ventilate your home which would mean installing permanent ventilation. As a general guide, you can remember that if the outdoor temperature drops, you should also decerase the humidity level in your home. And, if you lower your room temperature to conserve energy you should also lower the humidity to decrease condensation. Cut the moisture, cut the condensation. It's really that simple.

Technical Bulletin from Cardinal Glass IG:

EXTERIOR CONDENSATION ON HIGH PERFORMANCE GLASS: There have been some field complaints regarding condensation on the exterior glass surface of High Performance Glazing. The conditions when this happen are:
1.) Early Morning
2.) High Dew Point
3.) Clear Night Sky
4.) No Wind
On a clear night, the effective temperature of the night sky may be as low as -40 degrees F (regardless of what season it is). The exterior surface of the HP glass "sees" this cold temperature and loses heat by thermal radiation. The high thermal resistance of the HP glazing does not allow sufficient heat from the building to conduct to the exterior glass. The net effect is that the exterior glass temperature drops. If this temperature drops below the dew point of the outside air, condensation forms on the glass surface. Condensation will disappear when the exterior glass temperature rises above the dew point, allowing the moisture to evaporate back into the air. Increasing the glass temperature requires either a reduction in the thermal radiation loss, an increase in the heat transfer through the glazing, or some combination of both. HP glass has a very low heat transfer rate so the only recourse is to wait for Mother Nature. When the sun rises, or the dew point drops, or the winds picks up, then condensation will evaporate. Condensation has been known to occur on exterior surfaces of a well insulated building. Prior to HP, levels of insulation for glass were not high enough to create this phemomena. Fortunately, the conditions required to cause the condensation can only happen at certain times a year and the evaporation of the moisture is fairly quick as the sunrise warms the air and glass surface.

Additional Sources on Condensation

"Basic Humidity Fundamentals and Related Characteristics": North Dakota Energy Extension Service Program and Cooperative Extension Service

"Facts About Window Condensation and Humidity": Builders New Home Warranty Program, Winnipeg, Manitoba, Canada.