Patrick from Richmond BC is complaining of condensation in his bedroom windows. Why is it that our bedroom windows seem to fog up more often than any other windows in the house?
Condensation is caused by a combination of low temperatures and high humidity. We tend to keep our bedrooms cooler than other rooms in the house, and we tend to keep them closed up as well, trapping more humidity that an actively used room. Also, breathing all night is a moisture producing activity. All of this added together can just make that small difference that tips the balance between dry or wet windows.
Unless there is a cold air return directly in the bedroom, your bedroom door should have a space under it of about an inch. If it sits tightly on a shag rug, the furnace cannot bring much warm air into the room and hence will not force a change of air in that room. Also make sure that nothing is blocking the flow of air from the floor register up onto the window as this movement of air will also help to remove moisture and warm up the window, two actions that reduce condensation.
When all of that doesn't work, and especially if there are condensation problems on other windows in the house, then you need to exhaust more air out of the house, either through exhaust fans, or whole house air change systems. This will reduce the relative humidity in the house as a whole, something important on the Wet Coast of BC. Look up HRV in the Nuts & Bolts to get more details on ventilation systems.