Winter humidity levels
In the winter, we can also have too little moisture in the house. Because the cold outside winter air is so dry, it affects the indoor relative humidity when it enters our homes.
During the heating season, when the outside air temperature is below 15º, the relative humidity should not exceed 30% and in very cold weather, the humidity will need to fall below 30% to prevent condensation or frost on windows.
The University of Minnesota has developed guidelines for the minimum recommended humidity levels for houses. Based on a 70ºF interior room temperature, engineering studies established the following guidelines:
Outside Temperature Inside Humidity
20º to 40ºF Not over 40%
10º to 20ºF Not over 35%
0º to 10ºF Not over 30%>
-10º to 0ºF Not over 25%
-20º to –10ºF Not over 20%
-20ºF or below Not over 15%
These guidelines do not guarantee that condensation will not appear on mirrors or windows. Factors such as closed blinds or drapes may require you to decrease the relative humidity in your house below these guidelines.
A good rule of thumb for controlling relative humidity in the winter: if frost or condensation forms on your windows, the humidity is too high and you should turn down the humidistat. If your hardwood floors start to separate, the humidity is too dry and you should turn up your humidistat. You may need to regularly adjust the humidistat setting and the HRV setting to properly control the humidity in your house.
Typically you should not need to use a humidifier in the winter because of the amount of moisture that is generated during your daily activities. However, if you find that the humidity is too low, you may need to resort to using your humidifier.
Summer humidity levels
In the summer the relative humidity should not exceed 55% in the main level of the house with proper dehumidification and air conditioning. You should not operate the humidifier during the summer months. If your hardwood floors show cupping or buckling, the humidity may be too high. This might also be due to a water leak in your house. You should close windows to keep warm humid outside air from entering the house. Using a dehumidifier or the air conditioner to help dry out the house may be necessary.
RELATED LINKS AND FILES
Home Moisture (Acrobat - 487K)