The humidity level in your home affects your health and comfort. Too much or too little humidity can cause a number of concerns.  Some of these are only nuisance symptoms, but others could be far more serious. Many Canadians are familiar with the effects of relative humidity during the winter when we heat our homes and keep the windows closed, reducing indoor air circulation and ventilation. 

Common symptoms of too little humidity are chapped skin and lips, scratchy nose and throat, breathing problems, static and sparks, and problems with electronic equipment. Long term effects of too little humidity are continued discomfort and damage to furniture and other items. 

Conversely, too much humidity is indicated by condensation on your windows, musty smells, wet stains on walls and ceiling, and mold in bathrooms. Over time, this excess moisture can damage the home and its contents and contribute to several health problems.

If you suspect that there may be a humidity issue in your home the first step in the diagnosis is to determine the relative humidity (RH) of the air circulating in your home. Simply put, RH is a measure of actual amount of moisture or water vapor contained in a given volume at given temperature relative to the maximum, expressed as a percentage. Warm air has the capacity to contain more moisture than cold air. RH is said to be 100% if the air contains the maximum possible amount of water vapor at a given temperature.

So, what is the appropriate amount of moisture contained within the air in your home? The experts say that a relative humidity between 30 and 50% is a good rule of thumb. The actual number does fluctuate season to season, home to home, and even room to room. However, within this range you can improve not only the health of your home but your own personal health as well.

A small, inexpensive and easy-to-use instrument called a hygrometer (sometimes referred to as a humidity sensor or relative humidity indicator) can measure the humidity level in your house and confirm whether the house has too much or too little humidity. They are available in mechanical and electronic versions. The mechanical hygrometer will cost you between $7 and $10 with the electronic models being a little more expensive, running between $15 and $60.

Hygrometers are available at hardware stores, department stores, building supply stores and even electronics stores. Hygrometers are usually sold wherever you would buy a room thermometer. Hygrometers and room thermometers are often combined into a single piece of equipment. Once you have determined your home’s RH you can decide the appropriate course of action.

In winter when our homes are sealed up against the cold, proper ventilation is often an issue. This lack of fresh air movement and low exterior temperatures can make RH issues more prevalent than in summer.

Low RH can be caused by cold dry air leaking in around windows and doors. Taking measures to seal up the offending areas will generally improve humidity, with the added bonus of lowering your heating costs. However, if you continue to get sparks off the cat despite undertaking draft management measures you may have to install a humidifier.

Humidifiers can either be stand alone or attached to your furnace. Ensure that they are installed and maintained properly as they have the potential of contributing to mold problems.

Conversely, if your home is too damp you should initially look for possible sources of moisture. The usual suspects are leaky roofs, leaky plumbing, damp basements, and too many plants. A natural gas range and hang drying laundry also contribute to humidity. If you have satisfied yourself in the management of these sources of excess humidity, then you may need to add exhaust fans in bathrooms or a heat recovery ventilator (HRV).

To sum up, your home can either be too damp or too dry. Either one of these conditions brings with it a different host of problems. The good news is that once you have used your hygrometer to diagnose the problem you can take action to solve the problem.  The reward will be a healthier, more comfortable home for you and your family.

 --source: CMHC / Canada Mortgage and Housing Corporation

Back to top

Previous | Next: VOC's and Off-Gassing

Articles