This summer's plus 30 Celsius temperatures have taught a lot of Canadians about humidity -- the great compounder of heat discomfort. But did you know that high humidity can also make things uncomfortable for your home?

When moisture builds up to levels that encourage mold, air quality problems arise. Molds grow on paper, drywall, wood, paint and wallpaper, caulking and many other moist surfaces releasing spores, toxins and unpleasant odours. Air that is "too damp" can cause itchy skin and nasal passages, dust mite growth, ongoing condensation on windows, water damage to materials and even rot of wood materials within walls and elsewhere in your home.

In hot, muggy weather, resist the urge to throw open windows. When humidity levels are high, you'll increase interior moisture levels without gaining much relief from the heat. Wait until there is a dry spell to air out your home or cottage, then there's less chance of moisture problems. Air conditioners that remove water from incoming air as they cool are an asset.

Moisture cannot be escaped. It is continually released into your home by daily activities like cooking, showering and running the dishwasher or washing machine. Even human activities like breathing and perspiring are significant sources.

The amount of moisture in the air is normally measured as relative humidity -- the percentage of the maximum amount of moisture the air could hold at a specific temperature. When the relative humidity is greater than 100 per cent, moisture will condense. Warm air holds more moisture than cool.

According to the Canada Mortgage and Housing Corporation (CMHC), the "right" relative humidity in your home is less than 50 per cent -- below the point at which mold growth is likely. For instance, humidity levels in bedrooms should be 40 per cent or less to discourage dust mites that irritate those with allergies and asthma. If there is condensation on your windows in cold weather, the relative humidity should be lowered to 30 per cent.

Caution: Upgraded, energy efficient windows can support a higher than recommended level of relative humidity before tell-tale condensation occurs. When concerned, measure relative humidity using a hygrometer, available at local hardware stores. Mechanical hygrometers are relatively inexpensive while electronic versions are usually priced under C$80.

Here are a few tips for reducing interior moisture levels and, therefore, pollutants in your home or cottage:

  • Locate the moisture source before buying a dehumidifier or undergoing renovations.
  • Deal with leaks or floods as quickly as possible before they cause serious problems. For example, grade soil away from the building and repair or replace eaves troughs so they function properly.
  • Ensure your home has adequate air exchange with the outdoors, good air circulation and proper heat levels during winter.
  • Vent clothes dryers outside and use bathroom fans to remove moisture.
  • Select paint and decorating materials based on their ability to relieve moisture accumulation and reduce mold growth.
  • Use a dehumidifier to prevent or reduce moisture problems.

Dehumidifiers use a heat pump, similar to that in an air conditioner, to remove moisture from the air. CMHC suggests that, when buying a dehumidifier, consider more than the price:

  1. The manufacturer's suggested size required for the home's square footage.
  2. Noise levels at low and high speed.
  3. The Energy Efficiency Factor, which is a guide to a dehumidifier's operating cost.
  4. How the unit is emptied, i.e. manual versus self-draining.
  5. Whether it has an automatic defrost feature.

A dehumidifier alone may not solve severe moisture problems. Take the necessary steps to reduce the amount of moisture in your home. Stop water issues before they arise.

When it comes to moisture in your home, an ounce of prevention is worth volumes.

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