What is Relative Humidity (RH)?

Relative humidity is defined as the ratio of the water vapor pressure or water vapor content to the saturation vapor pressure or the maximum vapor content at the temperature of the air or gas. The saturation vapor pressure in the air varies with air temperature: the higher the temperature, the more water vapor it can hold. When saturated the relative humidity in the air is 100% RH.

According to the EPA, the relative humidity recommended for houses is between 30% and 50%. This level of humidity is not always easy to maintain, especially in certain problem areas of the home. A dehumidifier is often needed in basements and crawlspaces where humidity can be very high. However, in the winter months, the use of the furnace may contribute to most parts of your home suffering from the opposite problems: a lack of humidity. Therefore, monitoring RH levels in your home will allow you to maintain all areas it at the recommended levels and deal properly with seasonal variations.

Examples of How Relative Humidity Changes Occur

On a 30 degree F day with an outdoor RH of 60%, the relative humidity indoors can drop to levels as low as 15% when the air is heated to 70 degrees F (as the air is heated it expands giving it the capacity to hold more moisture. If moisture is not added to the air as it is heated the RH level may drop considerably). If the outdoor temperature is 10 degrees F, the indoor relative humidity may fall to 8% or less. These are extreme levels of dryness. As a comparison, the average relative humidity in the Sahara Desert is 25%.

Since warm air can hold more water vapor than cold air, the relative humidity of the air can be changed by simply changing its temperature. If in the winter, outside air at 20 degrees F and 65% RH is drawn inside and heated to 70F without humidification, its RH drops to about 10%. In summer, outside air at 70F and 60% RH flows into a basement at 60F causing an increase in RH up to 82%. In Phoenix Az, Mesa Az, Tempe Az, Scottsdale Az, Chandler Az, Peoria Az, Glendale Az, Avondale Az, Queen Creek Az, Cave Creek Az, Carefree Az, and Gilbert Az the temperatures are very warm so this can have a direct effect on the relative humidity.

You can see from the above examples why it is important to measure and control relative humidity levels throughout the entire home or building, since the humidity levels in the air may change drastically through the heating and cooling processes. These processes can then lead to extreme highs or lows in the relative humidity levels indoors. Humidity is an important factor when it comes to mold growth. If you believe you have a mold growth problem contact F N F Restoration for an inspection. We will be able to determine if you need mold remediation or mold removal services. If you need either mold removal or mold remediation services it is recommended that we conduct a mold test to determine the full extent of the mold damage we will be working with.

If you suspect unhealthy conditions in your home due to humidity being too high or too low, it is prudent to utilize a tool known as a digital thermo-hygrometer (a.k.a. moisture meter or humidity sensor). This handy instrument digitally calculates temperature and measures indoor relative humidity levels. It can store the minimum and maximum temperature and relative humidity as well as provide up-to-date readings of the present conditions. Using a thermo-hygrometer is the best way to learn about and understand your indoor environment. This unit allows you to evaluated the RH levels in your home and understand the RH patterns, such as highs and lows, that exist.

If you do have excessive humidity, and see evidence of a mold problem (Signs of a Mold Problem), then you may need an air purifier to remove mold spores from the air.

Ionizers are typically better than air filters, since they can remove smaller particles from the air, and do not rely on particulate passing through them in order to remove them from the air.