Technical Condensation Information
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> Controlling Humidity
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> What Can Effect the Performance of Windows?
> Condensation on the Outside of Windows
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Condensation is the word used to describe what occurs when water vapour in the air is changed into liquid water on a cool surface. Air can hold only a certain amount of water vapour at any given temperature. If the temperature of the air is lowered by a surface, which is cooler than the air's maximum water-vapour holding capacity, condensation will occur.
When condensation appears on our windows, the immediate thought is that the window performance is inadequate. In reality the culprit is not improperly installed or leaky windows at all. Your new windows are warning you of a possible excess of humidity in your home. If this problem is ignored, it can become far worse than the condensation, and possibly form on your windows.
Interior surface condensation can appear on many different cool surfaces in your home, such as toilet tanks, cold water pipes, door hinges, windows and poorly insulated walls. The lower the level of humidity in your home the more likely you will be able to reduce costly damages.
Table 1 shows the maximum recommended relative humidity's for different outside temperatures. The chart shows that as the outside temperature drops, the relative humidity must also drop to minimize condensation. Improved ventilation will assist in reducing the amount of condensation, by increasing the temperature of the cold surface.
| Outside Air Temperature in Degrees C | Relative Humidity With Inside Air Temperature of 20 Degrees C |
|---|---|
| -30 or below | Not over 15% |
| -30 to -24 | Not over 20% |
| -18 to -12 | Not over 25% |
| -12 to -6 | Not over 30% |
| -6 to 0 | Not over 40% |
Sources of Moisture
The principle sources of moisture in a typical home are household activities, which vary with the living habits of the family. Some idea of the quantities of moisture released by these act ivies in a family of 4 is given in Table 2.
These figures show that approximately 7 - 9 litres of moisture per day may be introduced into a house with 4 occupants under normal living conditions. This level can increase to as much as 18 - 23 litres per day on washdays. An efficient humidifier may also increase this considerably. Moreover, when gas from a kitchen stove is burning a dishwasher is in use, moisture will be added to the air.
NOTE: Watering a large number of household Plants can also create a lot of moisture in the air.
Moisture Produced by Various Household Activities for a Family of Four
| Activity | Moisture Produced - in Litres |
|---|---|
| Cooking (3 meals per day) | 0.9 |
| Dishwashing (3 meals per day) | 0.5 |
| Bathing - Showers | 0.2 |
| Bathing - Tubs | 0.1 |
| Clothes Wash (per week) | 1.8 |
| Clothes Drying (per week) - indoors | 11.8 |
| Clothes Drying (per week) - With unvented dryer | 11.8 |
| Floor Mopping (per 10m sq.) | 1.4 |
| Occupants (family of four per day) | 5.5 |
When high relative humidity is a problem, steps should be taken to control the moisture sources. Although there is usually little that a householder can do to alter the normal cooking and bathing habits of the family, the weekly laundry should be dried outside or in a well ventilated space inside the house. Automatic dryers and gas ranges should be provided with an exhaust vent to the outside, and humidifiers should be disconnected.
Several cases of condensation have occurred in buildings constructed over an improperly drained or unprotected crawl space. As much as 45 litres of water per day may be evaporated from exposed soil beneath the building when the ground is wet and the surface is not covered with a water resistant membrane.
In new homes, considerable quantities of moisture averaging 2,200 litres may be released for the various construction materials. This will add considerably to the total moisture load during the initial 18-24 months of occupancy.
How to Control and Improve Ventilation
- Leave blinds and/or drapes open as wide as possible at night and open all window coverings during the day. This will increase the warm air circulation over the cool surface and increase temperature of the glass.
- Check the furnace filter and replace it if dirty. A dirty furnace filter will reduce the output of the furnace fan. A clean filter will ensure maximum flow.
- Turn your humidifier off during the winter and anytime the temperature falls below 0 degrees C.
- Always turn on the bathroom fan when bathing or showering. The best results are achieved when the fan is ducted directly to the outside. Humidistat controlled fans, which automatically turn on when the humidity exceeds the setting on the switch are also available. Running the fan will also help reduce the fogging of bathroom mirrors.
- Always turn on the stove fan when cooking. For best results, make certain the fan is ducted directly to the outside.
- Ensure your clothes dryer is properly ducted to the outside, no air leakage is present in the duct, and the duct is free of all blockages. Avoid hanging clothes indoors to dry.
- Ensure the fresh air intake for the furnace is free of all blockages. If your house has no fresh air intake to the furnace, have one installed.
- Ensure all hot and cold air registers are clear of any obstruction as this could affect maximum air circulation. Avoid the use of air deflectors. Air deflectors directed towards the room will result in ineffective circulation over the window area. Air deflectors directed towards the window can result in thermal cracks in the glass.
- Install ceiling fans in locations where heat registers are not located close to the windows. The increase in airflow will definitely help reduce condensation on these windows. Ceiling fans should be run continuously in houses where the relative humidity is above recommended levels.
- Floors wet from mopping can add large amounts of moisture. Run exhaust fans while floors are wet and avoid washing floors on extremely cold days.
- Wipe up any excess snow or moisture tracked into the house. The evaporation of this moisture will result in an increase in the relative humidity level.
- Run your furnace fan continuously. Most furnaces are equipped with a switch, which allows the furnace fan to operate even when the furnace is not producing heat. If your furnace is not equipped with this type of switch, have one installed.
- Open doors and windows periodically to allow the dry outside air to replace the moist inside air.
- Ensure there are no leaks in the water pipes or drains.
- Ensure window and door frames are caulked where they meet the exterior finish of the house. This reduces the possibility of cold air infiltration which may lower the inside temperature of the window or door.
- Remove interior screens in the winter to allow better ventilation over the window surface. Screens will hamper the flow of air over the interior surface
Condensation can be an early visible warning that the relative humidity in your house is too high. Following the above steps should ensure that the humidity level is balance to provide comfort for the occupants, as well as reducing the risk of moisture damage to the house, and condensation on the windows.
