Humidity is the amount of moisture or water vapour in the air. You, your family and your pets produce moisture when you breathe or perspire. Even your indoor plants produce moisture. We add water vapour to indoor air through routine household activities: cooking, showering, bathing, doing laundry and dishwashing. And more moisture can enter your home from the surrounding soil through the basement or crawlspace.
When Is Humidity a Problem?
We need humidity for our comfort and health. But too much or too little humidity can produce a host of difficulties for householders. Some problems are no more than nuisances; others can be far more serious. Many are familiar to Canadians, often occurring during the heating season, when it is very cold outside, our windows are closed and indoor air circulation and ventilation are reduced.
Diagnosing Humidity Problems
Instead of guessing whether you have a humidity problem, why not find out for sure? A small, inexpensive and easy-to-use instrument called a hygrometer (sometimes referred to as a humidity sensor or a relative humidity indicator) can measure the humidity level in your house and confirm whether there’s too much or too little. Once you know for sure, you can decide what, if any, action is required. The two types most suitable for household use are mechanical hygrometers and electronic hygrometers. For most households, either type will perform satisfactorily if properly used and calibrated. Hardware and department stores, building supply and electronics stores often carry hygrometers. In fact, they’re usually sold wherever you’d buy a room thermometer, and the two devices are often combined in a single piece of equipment.
Using Your Hygrometer
Your hygrometer shows the relative humidity (RH) in your house. While the RH won’t be exactly the same in every room, one hygrometer per house is usually sufficient. You should place it where the humidity symptoms are most obvious, in the room you’re most concerned about or where your family spends the most time. Because they’re small, they can be moved around in your house from time to time. Don’t place your hygrometer near a radiator, a heat register, a chimney or in any other location where it could be affected by direct heat. A hygrometer doesn’t produce instant results. It may take up to two hours to give a stable reading in a new location or adjust to changes in relative humidity. Relative humidity is a percentage that indicates the amount of moisture in the air relative to the maximum amount the air can hold at that temperature. For instance, when air contains all the water vapour it can hold at that temperature, it has a RH of 100 per cent. If the humidity exceeds 100 per cent, moisture will begin to condense from the air. If the air contains only half the water it can hold at that temperature, the RH is 50 per cent. Warm air can hold more moisture than cool air, so the RH of a sample of air will change as the temperature changes, even though the actual amount of moisture in the sample does not. As a sample of air cools, the RH rises; when it warms, the RH falls.
How Much Is Too Much, Or Too Little?
Experts have developed rules of thumb to help homeowners make decisions about humidity levels. These should be used as guides only. Acceptable or comfortable humidity levels will actually vary from season to season, from house to house and between rooms in the same house. Some rules of thumb to prevent window condensation during the heating season:
> Normal recommended indoor RH: 30 to 50 percent
> When the temperature is -10 degrees C outdoors: 30 per cent
Humidity can be controlled. If the relative humidity in your home is too high, you can reduce it; if it’s too low, you can increase it. This may mean simple changes in your family’s habits, such as remembering to open or close doors or windows. Or you may need to install exhaust fans in bathrooms or kitchens to remove excess humidity. Very low indoor RH levels in winter may be due to cold, dry air leaking in from outside. Sealing up the house by weatherstripping and caulking will improve conditions indoors and may reduce your heating bills at the same time. Humidifiers – both stand-alone appliances and devices attached to your furnace – can be useful for increasing indoor RH levels. But remember that if they’re not installed, used and maintained properly, humidifiers can also be sources of excessive moisture and mould.
The Final Analysis
Humidity levels in your home can be too high or too low. In either case, problems can result.
A hygrometer will provide the information you need to determine whether you have a humidity problem. If you do have a problem, it can usually be controlled.
This article was supplied by CMHC (the Canada Mortgage & Housing Corporation). Go to www.cmhc-schl.gc.ca for other articles.