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How to reduce condensation on your windows?

  1. If your furnace is equipped with a humidifier or you run a separate humidifier unit, turn it off until the amount of condensation is reduced. Make sure that the humidifier and the setting switch are really working;
  2. Run kitchen and bathroom exhaust fans longer that your normally would;
  3. Make sure you clothes dryer is vented to the outside to keep the hot air and moisture from building up;
  4. Avoid hunging wet clothes inside to dry;
  5. If you have a fireplace, open the damper;
  6. The free circulation of air around windows is important. Leave drapes and blinds open as much as possible;
  7. Leave the furnace fan running rather than set on automatic.

If condensation is still a problem

Remember that windows don't cause condensation but a high humidity level can. If the above 7 Simple Steps don't solve the problem you might want to consult with an expert. Ask your heating contractor to check the airflow in the house and your humidifier.

What is condensation?

Stained ceilings, water streaming from windows and mold on trim and walls are all the common result of excessive water vapour in the air.

If we could only see the water vapour in our homes we would have a better chance of controlling it. We can't see water vapour, but we can see it's effects. The most common is condensation on the inside surface of your new windows. The fog, or in severe cases, the frost that forms on the glass is a sure tell-tale sign that the humidity level in your house is too high.

Condensation problems arise because air can hold only a limited amount of water vapour at any given temperature. Cold air can hold less water than warm air.

When air at a given temperature contains all the water vapour it can hold, it is said to have a relative humidity level of 100%. If it contains only half the water vapour it can hold at that temperature, then the relative humidity is 50%. If the temperature changes but no water vapour is added or removed, then the relative humidity will also change. It will increase as the temperature falls and decrease as the temperture rises. Relative humidity will rise as the temperature falls until the "DEW POINT" is reached, that is, the temperature at which the air can hold no more water vapour. Any further decrease in temperature will cause some of the vapour to condense as fog when the temperature is above freezing or as frost when it is below freezing.

It should be pointed out that a little fogging at the lower corners of the insulating glass units is nothing to be concerned about. Heavy fogging or worse, ice formation on the glass surfaces is a cause for concern. It is symptomatic of invisible moisture damage that could be happening in other parts of your home. Household humidity is a modern problem. More and more of us are living in "air tight" homes, they are more economical to heat and cool and easier to keep clean but we have created another problem and that is lack of air exchange and moisture traps.

Sources of moisture

The principal sources of water vapour in today's homes vary with lifestyles but the following is just a small list of normal daily activities and the water vapour they introduce per day.

Cooking (three meals a day) 3-4 lbs
Dishwashing 1-2 lbs
Shower or Bath 1-2 lbs
Weekly Laundry 30 lbs
Occupancy (family of four) 12 - 15 lbs


How much is enough

As stated before, we need some humidity in our homes to be comfortable. A house that is too dry is just as bad as a house that is too humid. Symptoms of a dry house are sore throats, itchy eyes, nosebleeds, and dry skin to name a few. Other, not so obvious symptoms are static electricity, cracked and dried out furniture and a constant feeling that the house is colder than it really is. Your new windows are a great barometer of just where your humidity level should be. "NOT ENOUGH TO FOG THE GLASS BUT JUST ENOUGH TO FEEL COMFORTABLE."

There are naturally more sophisticated means to check the humidity levels in your home from simple, inexpensive hygrometers to more complicated "wet and dry" bulb hygrometers. There are even inexpensive digital units that will measure temperature and humidity levels available at most hardware stores.

In the following chart are the recommended safe humidity levels based on outside temperatures for an interior household temperature of 70 degrees F.

-20 Deg. F. or below not over 15%
-20 Deg. F. to -10 not over 20%
-10 Deg. F. to 0 not over 25%
0 Deg. F. to 10 not over 30%
10 Deg. F. to 20 not over 35%
20 Deg. F. to 40 not over 40%