Measuring Humidity in Your Home

Humidity is the amount of water vapor in the air. Indoor air increases in humidity as we go about daily living. We add water vapor to indoor air through routine household activities such as showering, cooking, dishwashing and breathing.

We need a certain amount of humidity for comfort and health. However too much humidity often can be seen in the wintertime when homes are closed up and ventilation is limited. Usually it is seen as condensation on windows, musty smells, and mold growth. Low humidity can cause static sparks, dry skin and scratchy nose and throat.  High or low humidity levels can also damage wood furniture and flooring.

Using a Hygrometer.

In order to control humidity in your home, it is first necessary to measure it. This is done using an inexpensive instrument called a hygrometer available at most large hardware stores or garden centres. These instruments measure relative humidity (RH).  What that means is they measure the amount of moisture in the air relative to the maximum amount of moisture that the air could hold at that temperature. RH is expressed as a percentage.  For example if the air temperature is 70 degF and the air contains all the moisture it can hold at that temperature, then the RH is 100%. If the same air contains only half the amount of moisture, then the relative humidity is 50%. RH changes with temperature. Warm air is capable of holding more moisture than cold air.

There are two types of hygrometer, mechanical or electronic and either type is suitable. Hygrometers are relatively inexpensive and not particularly accurate devices so variations of plus or minus 2% can be expected. This is quite accurate enough for most indoor applications. Follow manufacturer’s directions for calibration of the units if necessary.

At any particular time the RH in a home will vary from floor to floor or room to room. Choose the area you wish to measure and leave the hygrometer in that location for a couple of hours before taking a reading.  When moving to other locations always allow a couple of hours for the unit to stabilize.

What should the humidity be in my home?

There are no strict rules for humidity levels. Some people are more comfortable at lower humidity levels than others. However, the experts generally agree that maintaining a level of 30% to 50% during the heating season is advisable. This will prevent moisture condensation on most double glazed windows and protect wood furniture and flooring. Generally the lower the temperature outside, the lower the indoor RH should be. When outdoor temperature is 14degF (-10 degC) or below then recommended RH is 30 %.

How do I adjust the humidity in my home?

Ideal humidity should be between 30% and 50%.

In summer time humidity can be controlled by using a dehumidifier or running an air conditioner.  Either unit will reduce the moisture content in the air. Dehumifiers are not as efficient as central air conditioners and are more suitable for smaller areas or a specific room.

In winter time, high humidity must be controlled by ventilation, increased  air flow and reduced moisture generation. If condensation is visible on windows then it is likely that condensation is occurring in other cold areas as well. Warm, moist air travels through the building structure and will condense when it reaches its dew point (a cold surface). Excess moisture plus a food source encourages mold growth.

  1. To minimize moisture generation. Always operate ventilation fans when cooking , bathing or showering. Bathroom fans are relatively low flow and should continue to run for a minimum of 20 minutes after showering.
  2. Deal with any problems such as a damp basement, roof leaks, excessive plants, excessive aquariums and any other sources of moisture.
  3. If you have a humidifier on your furnace. Turn it off or turn the humidistat down to add less moisture to the recirculating air.

If low humidity is the problem:

  1. Air tighten the house. Seal all air gaps where cold outside air can enter the home. This includes vents dryer ducts, electrical outlets
  2. Install a humidifier. Humidifiers, both stand alone and furnace mounted will increase indoor RH levels. Be aware that they can also be sources of excess moisture and mold in your home so adjustment and ongoing maintenance will be necessary.
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