Air exchangers are used to exhaust excess of humidity during winter season. Consequently, it is normal to experience vapours and ice build up on windows during cold weather. Many factors may cause this situation: Poor insulation, quality of windows, heating temperature, obstruction in front of windows (e.g.: blinds, curtains, etc.), prevailing winds, drastic changes in outside temperature.
Do not close your blinds or curtains completely, because that will prevent the heat from reaching your windows, which fosters condensation. Remove interior window screens if you can.
Do not delay turning on the heat in your home, especially in the basement. This will remove the humidity that has accumulated over the summer months.