top of page
  • Writer's pictureJeremy Cook

Heavy Condensation on Windows? Here is the Answer

Are you concerned about excess moisture buildup on you windows?  Do you feel like your builder has let you down?  Well, let's talk about what causes condensation and how you can help reduce it.

Why Condensation Forms:

     -Warm air holds more moisture than cold air.

     -There is an extreme difference between inside air and outside air temperatures. #yycbrrr

     -Windows are the coldest surface in your home.  

     -Condensation forms when warm moist air inside your home meets with the cold windows and skylights cooling the air thereby turning the water vapour into water droplets that attach to the windows. 

     -The amount of condensation on windows has nothing to do with the home builder and everything to do with how you live in the home.  Condensation on walls or ceilings may indicate an area of missing insulation and that would be something to talk to your builder about.

Condensation is Normal:

     -Calgary is experiencing its coldest temperatures in 2 years!  This means that over the last two years you probably haven't noticed much condensation on your windows because the weather has been warm and much closer to the interior temperature of your home.  Now that the weather has turned on us dipping temperatures down to -28°C we can expect to see excess condensation on windows.

     -Older homes were MORE breathable meaning that air (and moisture) was able to move in and out of the home with relative ease.  Heating costs were higher but condensation was rarely an issue.

     -Newer homes are LESS breathable.  Increased insulation and vapour barrier, reduced air leaks around windows and doors, and sealed combustion appliances like furnaces and hot water tanks reduce breathability.

Types of Windows:

     -Single Pane: Build up with the most condensation and frost on cold days because they are colder. Are typically not functional during winter months.

     -Double pane: Normal buildup.  May or may not be operable depending on your ability to control moisture in your home.

     -Triple Pane:  The least amount of condensation because the windows are warmer, producing less condensation. 

Common Sources of Moisture:

     -You and Your Family.  The more people in the home, the more moisture. 

     -Pets & Fish Tanks

     -House Plants.  House plants create a huge amount of humidity.



     -Dirty laundry.  Piles of dirty laundry increase moisture by first removing it from your skin and then laying around the house drying and sending that moisture into the air.

     -Open Flames from candles and fireplaces.  Burning anything creates CO2 and water vapour.


A Place To Start:

     -Ensure your dryer vent is properly connected and there are no holes in it.  The dryers job is to remove humidity from the home and you want to make sure all of that moisture is leaving the home.

     -Ensure your range hood above your cooktop vents to the exterior of the home.

     -Turn down, or turn off your humidifier.  The water shut off is typically located above the hot water tank if you are experiencing excess humidity.  Humidifiers can get stuck in the ON position creating moisture issues inside the home.  For best results turn the water completely off to rule this out. 

     -Add or improve the weather stripping around the attic access hatch.  You will likely notice signs of condensation (frost, mold) around the interior edge of the hatch opening after you remove the hatch door.  This indicates the weather stripping is insufficient.  

     -Seal air gaps around windows with caulking.  Use a smoke pen to locate air leaks and seal them.

     -Open the heat vents.  Allow warm air to circulate the home.

     -HE Furnaces: Check your furnace exhaust vent for water droplets or loose connections.  Excess moisture can be added to the home this way and it is also a serious health risk.  Cold exterior temperatures is the best time to check as you are more likely to see water dripping. Contact an HVAC specialist immediately if you find water. 

     -Ensure attic hatch doors are insulated and weatherstripped to prevent condensation.  The access into the attic is another common area of condensation.

Consistent Ways To Fight Back Against Increased Humidity Every Day:

     -Run bathroom fans when showering, and for up to 30 minutes after leaving the bathroom.

     -Use the range hood fan when cooking.  Especially true of gas ranges.

     -Avoid hanging clothes to dry.  Use the "air fluff" setting on the dryer to move that moisture outside without shrinking your clothing.

     -Open blinds to allow airflow around the window, warming the window, leaving less condensation. If you have top down blinds, leave a 2" gap at the top and bottom of the window to allow air to circulate. If you have slats, direct the slats upward and open the blinds 2" at the bottom to improve airflow.

     -Open closet doors to closets that share an outside wall.  Clothes and storage inside closets can limit airflow creating a risk of condensation (and eventually mold or mildew) on the outside wall.

     -Clean away excess condensation using a towel to avoid damage to the wood trim around the window.  This will also help in that it will prevent the condensed moisture from becoming airborne again as outside temperatures warm.

     -Turning up the temperature at the thermostat a couple of degrees will warm the house air increasing the amount of moisture it can hold.  This can help evaporate built up moisture from windows.

-and Pray for a Chinook!

Ventilation Options:

 -These systems are installed in new homes to help exhaust excess moisture common to new construction methods. The use of these systems will help get rid of moisture only if you are also following the tips above to reduce moisture levels in the home at the same time. Some of these venting methods can increase heating costs as described below. It's basically like opening a window without actually opening a window (except the HRV). 

     -HRV (Heat Recovery Ventilator) is the best option.  This box mounted near the furnace exchanges air bringing in dry air from outside and exhausting moist interior air.  The best part is that it uses the outgoing air to warm up incoming air allowing you to exchange more air efficiently. I have an HRV in my home and I use it 24/7/365. You get fresh air from outdoors which is typically healthier air than inside air, and it removes moisture to whatever extent you like using an adjustable control panel. 

     -Most homes in Calgary built in the last 15 years have a primary fan, of one type or another, that is used to help remove moisture. Principal exhaust fan controls are typically mounted near the thermostat.  This switch can be set up in a few different ways by the builder.  Depending on the method, you may want to limit your use of this ventilation method as it can remove between 40 and 80 cubic feet per minute of warm house air (you have already paid to heat) and can create negative pressure causing issues with natural gas appliance venting.

          a) Switch turns on the highest bathroom fan in the home. This helps pull air up and out of the house.

          b) Switch turns on the furnace fan. This moves air around the house without heat. It can cost additional money to run such a large fan continuously and can make the home feel draughty as it moves unheated air.

          c) Switch turns on both the furnace fan and upper bathroom fan.

          d) Switch turns on a small fan near the furnace drawing in cold outside air into the furnace for heating before distributing through the home. I would not recommend running this fan in colder temperatures as you will incur increased heating costs associated with drawing in that cold Alberta air. I would recommend running it on warmer days.

The Bottom Line:

-Some humidity on windows is normal and unavoidable on cold days.

     -If you live in a home built in the last 15 years, you may need to adjust your lifestyle around reducing moisture levels in the home.

When should I Be Concerned?

If moisture and condensation are affecting interior finishes like drywall or if there is moisture between the panes of glass contact a professional for further evaluation. 

2,292 views0 comments

Recent Posts

See All

10 Things To Check Before Going On Vacation

What you need to do depends on how long you are planning to be gone.  If you're just leaving for the weekend, I suggest leaving things as is and simply turn off the main water supply in the basement i


bottom of page