Measuring Humidity in Your Home

Straight Facts About Humidity

Many of our customers ask about humidity in their home.  Problems may occur when there is too little or too much moisture in the environment you live in.  Too much can lead to health problems, and mold/mildew accumulation in your home and potentially cause damage due to rot.  Too little can cause natural materials (wood products) to shrink and distort, causing cracks and squeaks in the home.  We found this article from the CMHC website that is very useful;

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. More moisture can enter your home from the surrounding soil through a basement or crawl space.

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 of the problems are no more than nuisances; others could be far more serious. Many are familiar to Canadians. They often occur during the heating season when our windows are closed, and indoor air circulation and ventilation are reduced.

Diagnosing the Humidity Problem

Instead of guessing whether or not you have a humidity problem inside your house, 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 relative humidity indicator) can measure the humidity level in your house and confirm whether the house has too much or too little humidity. Once you know for sure, you can decide whether any action is required and, if so, what action.

Relative Humidity

Humidity is normally measured as relative humidity (RH). RH 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 at a given temperature 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 that the RH of a sample of air will change as the temperature changes, even though the actual amount of moisture in the sample air does not. For example, as a sample of air cools the RH rises.

Humidity: How Much Is Too Much, How Much is Too Little?

Experts have developed rules of thumb to help homeowners make decisions regarding humidity levels in their house. The limits should be used as guides only. Acceptable or comfortable humidity levels will actually vary from season to season, from house to house, and even between rooms in the same house.

Rules of Thumb

To prevent window condensation during the heating season, the recommended indoor RH is 30 per cent to 50 per cent. When it is below -10°C (14°F) outdoors, recommended indoor RH is 30 per cent.

Taking Action

Humidity can be controlled. If the relative humidity in your home is too high, you can reduce it; if it is too low, you can increase it.

In summer, you can reduce house humidity levels by the use of a dehumidifier (see  Choosing a Dehumidifier) or by running an air conditioner.

In winter, a house that is too wet usually has some high moisture sources (for example, a damp basement, roof leaks, many plants). Deal with these problems first. If high humidity persists, you may need to make simple changes in your family’s habits, such as remembering to open or close doors or windows. Or, you can install equipment, such as exhaust fans in bathrooms or a heat recovery ventilator (HRV), to remove excess humidity.

Very low indoor RH levels in the winter may result from cold, dry air leaking in from outside. In this case, sealing up the house by weather-stripping and caulking will improve humidity conditions indoors and may reduce your heating bills at the same time.

If low humidity problems persist, despite air-tightening the house, consider the use of a humidifier. Humidifiers — both stand-alone humidifiers and humidifiers attached to your furnace — will increase indoor RH levels. But if they are not installed, used and maintained properly, they can also be sources of excess moisture and mold in your home.

Final Analysis

Humidity levels in your home can be too high or too low. In either case, problems can result.

A hygrometer can provide the information you need to determine whether you have a humidity problem — but it must be accurate to be useful.

If you have a humidity problem, it can usually be controlled.

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