Keep High Humidity In Check - June 27th 2011


Keep High Humidity In Check


I have now covered how to select the proper furnace for your home, how to finish your basement, and what to use to insulate your home. All of these upgrades affect how your home works as a system, one of the changes can be a difference in the relative humidity or moisture level in your home.

Condensation on windows is the most noticeable sign that you have excessive humidity levels in your home. A little condensation, now and then is to be expected but high humidity often causes consistently foggy windows that should be addressed.

Condensation is a natural occurrence which can happen on all surfaces in the home when moisture levels are too high. Inefficient windows (i.e. single pane with aluminum frames) or inadequate ventilation can result in condensation, frost, or pools of water on windows and sills. When water vapor comes in contact with a surface which has a cooler temperature (this is called dew point), such as windows, the vapor turns into visible droplets of moisture, which can be seen on the glass. This water vapor also adheres to the walls, which can be a more serious problem because it can penetrate walls and constant excess moisture can lead to mold, mildew, and deterioration of your drywall.

Humidity in your home comes from everyday living; steamy showers, boiling water, dishwashers, washing machines, dryers, wet and snowy boots and clothing, and many other sources. Poorly insulated crawl spaces can increase the humidity in your home often resulting in a musty odour.

It is important to remember that there is no such thing as a condensation free window and windows themselves do not cause condensation, they simply prevent moisture from escaping to the outside. Seeing condensation build-up on your window signals that steps need to be taken to reduce the moisture in the air inside your home:

- Regularly use ventilation fans in kitchens, bathrooms and laundry rooms to circulate the air.

- Squeegee your tub surround and shower enclosure, then use your towel to dry off the excess moisture and leave your bathroom ventilation fan on for at least 1 hour after every shower.

- Open interior doors and windows to circulate airflow.

- If you have a humidifier or dehumidistat set them to the correct outside temperature settings.

- Make sure you have adequate ventilation through your soffits, roof ridge, basement and crawl space.

- Install energy efficient windows.

Always think of your house as a system keeping in mind that one reason you are seeing these changes in your home after your upgrades is your new high efficient heating system operates differently than your old furnace.

Exhaust ventilation has to be provided to accommodate increased relative humidity in the home otherwise high humidity may be the outcome.

Relative Humidity Settings

Moisture levels must be controlled within the home. The following settings are recommended:

Relative humidity should be as follows:

Outside Temperature / Relative Humidity (Inside Home)

Above 0oC / 50% to 60%

0 to - 12oC / 40%

-12 to - 18oC / 35%

-19 to - 24oC / 25%

-25 to - 30oC / 20%

-31oC or below / 15%

NOTE: Digital Humidity indicators (Hygrometers) are available from most local hardware stores.

Heat Recovery Ventilators (HRV) and exhaust ventilation extract moist, stale air from the home allowing fresh air to come back into the home through make-up air vents. An additional benefit of an HRV is that it will bring fresh air from outside into the home, and while that process is occurring the fresh air is being warmed or cooled depending on the time of year within the HRV.