During the winter season, we at McCallum Aluminum Limited sometime receive calls regarding the problem of water collecting on window surfaces (know as condensation) on their new windows once the furnace begins operating. This is due to moisture that used to escape around their old windows that is now contained within the envelope of their house. Callers recognize that this condensation results in obstructed visibility, reduction in the intensity of natural lighting and most importantly deterioration of interior finishes (rings, stains, peeling paint) and mould growth. Keep reading to learn more.

We have compiled a number of publications from various government agencies (i.e.- Natural Resources Canada, Energy, Mines and Resources Canada), window manufacturers (Gentek Building Products, North Star Manufacturing) and construction industry publications (Ontario Home Builder). We have put together their recommendations and suggestions into what, we hope, is a valuable resource for our customers.

The basic concept to remember is that warm air carries a large amount of moisture. When this air comes into contact with a surface that is cooler than itself, the moisture naturally condenses onto the cooler surface. More simply, the warm air from your furnace hits the cooler glass of your windows & patio doors and collects on the glass. This is especially true if your home has been made so air tight that there is minimal air circulation to the outside. For example, warm air trapped behind heavy draperies during the night cannot circulate and therefore collects on the glass. Opening the draperies usually allows full air circulation so that there is less of a condensation problem. We see this problem more often with newer energy-efficient homes. There are two solutions to either decrease or eliminate this problem: raising the glass surface temperature and/or decreasing the relative humidity of the indoor air. At McCallum Aluminum, we recommend that you first follow the suggestions below, gleamed from the afore mentioned publications, in order to decrease the humidity levels in your home.

  1. Disconnect or turn down any humidifiers connected to your furnace or any individual humidifiers running in rooms in your house.
  2. Do not store wood in the house.
  3. Avoid hang-drying laundry in the house.
  4. Cover any earth floors in basements or crawl spaces with a moisture barrier.
  5. Install a sump pump to remove excess moisture from the soil under the slab.
  6. Fix any water leaks into the basement.
  7. Do not allow any standing water in the house or against the foundation wall.
  8. Make sure that the ground slopes away from the foundation wall and that there are properly functioning eavestroughs around the house.
  9. Ventilate kitchens and bathrooms (by use of a fan or by opening a window a bit) during use.
  10. Move plants away from windows (water vapour is released directly onto glass).
  11. Ensure that clothes dryer & gas appliances are vented properly to the outside.
  12. Although it cannot alone eliminate the problem, install a de-humidifier.
  13. Do not cover windows with heavy curtains as this restricts air flow over glass.
  14. Keep all rooms, even if unoccupied, heated to a minimum of 10C (50F) as condensation will occur in unheated rooms.
  15. Leaving the damper open in a fireplace, or lighting a fire will increase ventilation and assist the rate of air exchange. Opening a window, even a tiny bit, in your basement will increase ventilation during both the day and evening/night hours.
  16. If you have a hot air furnace, install a direct fresh air intake (especially if you have electrical heat or a high efficiency furnace where this is no conventional chimney).
  17. If you have storm windows installed, condensation can occur for two reasons:
    1. The storm window is sealed so tightly that the outside, drier cold air does not circulate in the cavity.
    2. Excessive passage of moist, indoor air into the cavity because the prime window is a loose fit and needs sealing or replacing.

HUMIDITY FACTS: Did you know?

  • It only takes 2.8 litres (5 pints) of moisture to raise the humidity in a 1000 sq. ft. home from 15% to 60%.
  • Unvented cooking for a family of four generates 0.92 litres (1.6 pints) of moisture a day. If a gas stove is used, add 1.24 litres (2.2 pints) a day.
  • Dishwashing for a family of four generates .45 litres (.8 pints) of moisture a day.
  • Washing clothes for a family of four generates 1.96 litres (3.5 pints) of moisture. Clothes drying (unvented) for a family of four can generate 11.97 litres (21.1 pints) of moisture.
  • Mopping a 80 sq. ft. floor generates 1.09 litres (1.9 pints) of moisture.
  • Each bath generates .05 litres (0.1 pints) of moisture.
  • Each shower generates .23 litres (0.4 pints) of moisture.
  • Through normal respiration and skin evaporation a person can generate 4.23 litres (7.6 pints) of moisture a day.
  • House plants can generate .48 litres (0.8 pints) of moisture a day.