I have been so frustrated this month with the amount on condensation on my EXPENSIVE bedroom windows. I know it's because we don't have adequate ventilation - and because my new pleated shades are very energy efficient. Every morning I am wiping excess condensation from around the edges of my windows so the wood doesn't stain. Bedrooms are susceptible to high humidity because you breathe (or snore) heavily all night....or take a shower at bedtime...then the room inside is humid, and the night air is cold. Perfect conditions for condensation on the windows.

The warmer the air, the more water vapor it is able to hold. Cold surfaces cause condensation, and the air immediately adjacent to the glass is chilled by the outdoor temperature. Where is the coldest surface in a house during the winter? Usually, windows have the coldest surface, which expalines why condensation - in the form of fogging or forst - is common on cold days. Cold surfaces can also occur at thermal bridges, which are locaitons where there is very little insulation or where structural members extend through theinsulation from insdie to outside. Examples of thermal breidges include exterior corners and wall/ceiling intersections, according to the Canadian Office of Energy Efficiency.

You may be surprised to learn that condensation caused by cold surfaces can also be a problem in the summer. Usually, in late spring or early summer the ground has not fully waarmed up from the previous winter. On warm, humid days condensation can occur on basement walls and floors that are in contact with the ground.

There are many moisure sources that can contribute to elevated humidity levels in winter: Occupants - 34=40 liters a week for a family of 4
Summer moisture absorbed by house and released in fall (20-40 liters /week for about 4 weeks)
Drying of construction materials in new construction (25-35 liters/week for the first 18 months)
Household activities such as showering, cooking, bathing, washing (15-20 liters/week)
Damp basement, craw space or sump pit (15-20 liters/week)
Drying clothes indoors (10-15 liters/week)
Humidifiers
Indoor pools, hot tubs, greenhouses, house plants and aquariums.

Indoor humidity levels are also influenced by air exchange, which has the effect of replacing moist indoor air with drier outdoor air during winter.

I'd love to hear your solutions for minimizing early winter condensation indoors!