If your windows are sweating (have condensation forming) then likely you have too much humidity in your house.

Many people find that when they buy a  new home or upgrade their old windows to new ones they get more condensation - That is true. Why?

Why new homes have more window condensation . . .

Most new homes are built very energy efficient. That means they have a sealed combustion furnace and are built very air tight. That also means minimal fresh air from outside coming in to dilute the humidity in the house.

If the house is built energy efficient and air tight you also won't run the furnace as much which is how you get fresh air into the home.  Unless you switch on the principal exhaust fan (located in the hallway near the thermostat) you won't be able to reduce the humidity.

HRV (Heat Recovery Ventilator)

If you have an HRV, that unit will run all the time and bring fresh air in and exhaust stale air out. It keeps the humidity steady and indoor air quality high. Most new homes SHOULD have one, but most homebuyers are not aware of these units and are more interested in granite counter tops than fresh air until the first winter when the windows start sweating.

Here are the maximum humidity levels you can expect to run your home before the windows sweat.



Average Moisture Sources per Week
SourceAdded Moisture – Liters
Average Family of 463
2 Pets                                                                30                  Drying Clothes      12
Gas Range      9
Refrigerator      9
3 Large Houseplants5
Hand Dishwashing   3
Bathing – 8X    3
Showers – 8X 25
Wet Basement       14
New Construction Materials (first 36 months)    5
Seasonal Moisture storage in materials    8
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Copyright Qualistat 2009-2012
OUTDOOR TEMPERATURE   MAXIMUM INDOOR MAXIMUM INDOOR
     RELATIVE HUMIDITY       RELATIVE HUMIDITY
Dual Glaze windowsTriple Glaze Windows
-30 Celsius  and Colder         16% at 21 Celsius 35% at 21 Celsius
-29 Celsius to -24 Celsius       22% at 21 Celsius40% at 21 Celsius
-23 Celsius to -18 Celsius       24% at 21 Celsius45% at 21 Celsius
-17 Celsius to -13 Celsius       28% at 21 Celsius50% at 21 Celsius
-12 Celsius to -6 Celsius        33% at 21 Celsius62% at 21 Celsius
-5 Celsius to +2 Celsius         40% at 21 Celsius68% at 21 Celsius

NOTE 1 - Minor sweating may still occur along bottom edge of window glass depending upon the spacer insulation and window material
NOTE 2 – Wind will have a dramatic effect on the glass temperature and decrease the indoor maximum relative humidity
NOTE 3 – air circulation across the window glass will decrease condensation on the glass as it warms the glass surface
NOTE 4 – Always leave curtains open, leave blinds up 10-12”, do not place furniture in front of windows blocking floor vents

This table was compiled by comparing Canadian Window manufacturers data


WINDOW CONDENSATION

In simple terms, when air cannot hold anymore humidity (vapour) it begins to turn to liquid, or sometimes referred to as "sweating"

Condensation on windows is an indicator of high humidity in a home. There are many sources of humidity that can cause your windows to sweat..
ATTIC CONDENSATION

When air from the house leaks into the attic, it condenses and freezes

That could be caused by

  • Poor construction techniques and workmanship
  • Disconnected Vents - Fans, Dryer, Kitchen Hood, Etc
  • Exterior high humidity entering the attic space through soffiting - IE Front door under large vented soffit area


To stop the build-up you need to prevent the humid air from entering.


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The Video on the right is a result of a false plumbing wall creating a dead space that has no seal to prevent air leakage - See Picture below top left
















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