Condensation

Useful Information to Better Understand How Your Windows Operate


Recommended Relative Humidity
The term “moisture” means the amount of water vapour in the air. Water vapour is produced by indoor plants as well as by daily activities such as preparing meals, showering, bathing, doing laundry and dishwashing.

Condensation Inside Windows
Condensation is the biggest moisture problem for windows. Some condensation on a window is not cause for concern because in very cold weather, all windows are prone to it. However, heavy condensation over long periods is a sign of problems. Most problems are caused by frost on the windows that melts quickly into streams of water without having time to evaporate.

Three factors explain the appearance condensation inside windows:

  • The temperature of the window glass facing inside;
  • The relative humidity indoors;
  • The temperature of the outside air.

Condensation on the surface of the sealed unit facing indoors is caused by ambient moisture, which must be controlled with respect to the outside temperature. In early fall, when the heating system is not on all the time, humidity inside the house can rise to around 60%, resulting in fogging on the glass facing inside.

However in winter, the ideal humidity for occupants is between 30 and 50%.

According to medical authorities, humidity below 15% is a respiratory irritant. When the outside temperature is below -10C, the recommended humidity is 30%.

For your convenience and to avoid condensation problems in cold weather, here are the recommended conditions:

30° to 25° C
25° to 18° C
18° to 12° C
12° to 6° C
6° to 0° C
20% maximum
25% maximum
30% maximum
35% maximum
40% maximum

When I got new windows, I noticed moisture collecting at the bottom, while my old windows did not do that. Why is this?
The new PVC windows are very air-tight. In contrast, old windows let strong drafts go through many cracks or fissures. So the air in the room was always changing.

Why Does the Air in a New House Have Such High Relative Humidity?
The woodwork, plaster and other new materials are still moist, and the air of the house absorbs this moisture. Therefore, until the material is completely dried, the humidity remains much higher.

How Can I Understand Energy Efficiency?
First determine your climate zone according to the following table:


In our beautiful province of Quebec, winter is not very generous in terms of hours of sunshine during the day. It is therefore not very useful to try to use solar power to heat our homes. Hence the importance of making the right choice of window glass units.

Our window units are designed to keep more of the heat inside. This leads to savings on the rising costs of heating and air conditioning.