What is humidity?
Humidity is the amount of moisture or water vapor 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 vapor to indoor air through routine household activities:
4. Doing laundry
6. And similar to activities
Also, more moisture can enter your home from the surrounding soil through a basement or crawl space.
Diagnosing the Humidity Problem
The easiest way to find out if you have a humidity problem is to purchase a hygrometer(referred to as a humidity sensor or relative humidity indicator). This will 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 to do.
Using Your Hygrometer
Your hygrometer will show the relative humidity (RH) in your house. Although the RH will not be exactly the same throughout your home, one hygrometer per house is usually sufficient. You should place it where the humidity symptoms are most obvious, in the room that you are most concerned about, or where your family spends the most time.
Don’t place your hygrometer near the following items:
2. Heat register
5. Air conditioner
8. Boiling pots of water
9. Direct sunlight
A hygrometer does not produce instant results. It may take up to 3 days to acclimate to its new environment. Also, they respond slowly to dramatic changes and may take up to 2hours to fully adjust.
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.
Ex)When air at a given temperature contains all the water vapor it can hold at that temperature, it has an RH of 100%. If the humidity exceeds 100%, 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%.
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 air does not. For example, as a sample of air cools the RH rises.
Calibration Made Simple
All mechanical hygrometers should be calibrated. Some are not properly set when they leave the factory. Others, even the best models on the market, may experience what is known as drift, which means that they do not hold their accuracy over long periods and need to be re-calibrated.
How Often Should You Calibrate?
Once you have calibrated your hygrometer, you can be confident that you are getting accurate readings. Even so, you should re-calibrate your hygrometer at least once a year to make sure that it continues to work properly.
Humidity: How Much Is Too Much, Or Too Little?
Experts have developed rules of thumb to help homeowners make decisions regarding humidity levels in their houses. 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.
Some rules of thumb to prevent window condensation during the heating season
- Recommended indoor RH: 30% to 50%
- When it is below -10oC/14oFoutdoors, recommended indoor RH: 30 percent