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Relative Humidity and Whole House Dehumidifiers

What is humidity?

As most people already know, humidity is defined as the amount of moisture in the air.  Relative humidity is a way to measure the amount of humidity present based on the maximum amount of humidity the air can hold.

Basics of humidity

The amount of moisture that air can contain is roughly based on its temperature.  Cold air can hold less moisture and warm air can hold more.  In the winter time your house is surrounded by cold air that doesn't hold as much moisture, so the conditions inside your home naturally try to match their surroundings.  This is why your house is typically dry in the winter (unless of course you are using a humidifier to add moisture).  The warmer summer air can hold more moisture, and therefore your house also tends to have much higher humidity levels in the summer time.

How do you calculate relative humidity?

How does this help to determine relative humidity?  Any temperature of air has a maximum amount of moisture it can hold.  The relative humidity is expressed as a percentage of the current moisture level relative to the maximum moisture level for the current temperature.  For example, when the inside temperature of your house is 68 F then 1 cubic meter of air can hold 18 grams of water (called saturation, or 100% relative humidity).  If the air contains 9 grams of water per cubic meter, then the relative humidity is 50% (9 / 18 = 50%).

How does relative humidity affect our comfort level?

Humans rely on moisture evaporating from our skin to help cool our bodies.  When the relative humidity levels are higher, less moisture can be evaporated from our skin, which makes it feel hotter than it really is.  This effect is known as the heat index, which is a simple term used to describe how hot it feels to humans given a certain temperature and humidity level.  For example, if the temperature is 80 F, it will feel like it is 78 F when the relative humidity is 30%, but it will also feel like it is 85 F when the relative humidity is 70%.  2 or 3 degrees may not sound like much, but our bodies are very sensitive to small temperature changes and those 2 or 3 degrees will make the difference between an uncomfortable house and a house that is "just right".

Generally speaking, a relative humidity of 45% - 50% is most desireable inside your house.  At this level of relative humidity the temperature that your body feels is the same as the temperature indicated on your thermostat.  These levels are also high enough that your skin and lungs do not get dried out or irritated.

Why should I use a whole-house dehumidifier to manage my humidity?

In the summer time your air conditioner will naturally remove some humidity from the air as part of its natural operation.  Your air conditioning system does not, however, care what the relative humidity is, only what the temperature is.  Once it reaches the desired temperature it stops running, even if there is still a high relative humidity that makes our bodies feel a higher temperature.  This is where a whole house dehumidifier comes in handy.  With a dehumidifier running and keeping the humidity levels down in a desireable range, you won't have to over-use your cooling system to compensate for high relative humidity.  It is always going to be less expensive to remove humidity from the air than it would be to cool your entire house, which makes adding a dehumidifier a wise economic choice to supplement your air conditioning system.

In addition to making a more comfortable house for yourself, keeping the relative humidity in the 50% range has many other benefits.  Lower humidity levels preven furniture from drying out, and also inhibit mold and fungus growth.  The effects of mold growth in your house is beyond the scope of this article, but needless to say you do not want mold growing in your home.

How can I tell which dehumidifier is right for me?

High quality dehumidifiers are rated for the amount of moisture they can remove at AHAM, which is 80 F with 60% relative humidity.  On our website (and most others) this measurement is stated in Pints Per Day, which indicates how much water will be removed in a 24-hour period at 80 F and 60% relative humidity.  The AHAM rating allows you to compare each model's performance under identical and typical conditions.

Figuring out how much moisture you need to remove is a very scientific process (and one we will not get into here).  To make things easier for you, we have roughly converted the dehumidifying capacity of each model to indicate how many square feet of space it can handle.  When you look at a list of dehumidifiers on our site, you will not only see the capacity at AHAM in pints per day, but you will also see roughly how many square feet that model can handle.  Any model can certainly handle a smaller area than we rate it for (and larger models can dehumidify smaller spaces quicker and more effectively than can smaller models that have a rating closer to the size of your home).