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What the EPA Does Not Tell You About Indoor Humidity Levels

The EPA relative humidity guidelines for comfortable humidity levels in your home’s living space recommends maintaining 30%-50% RH.  Some EPA mold resources  recommend the higher end of acceptable relative humidity as high as 60%, but this is not true for your crawlspace.  And since this is a reputable government resource, many other industries and associations have based their standards and practices on these recommendations.  Unfortunately, this is very limited information and has been used as a guideline in more than what is applicable.  In fact, many industries have been misled and developed ineffective and sometimes harmful products and procedures that we all use in our homes.

For example.  AHAM, the Association of Home Appliance Manufacturers is the recognized trade association that sets standards to which most available home appliances will adhere.  They give a baseline for comparing performance of appliances.  For dehumidifiers, the baseline is Pints per day of water removal at 80°F and 60% Relative Humidity.  Yes, that does give a common point for comparing one unit to another, but who keeps their home at 80°F?  And 60% relative humidity is barely acceptable for healthy conditions.  Unfortunately for the consumer, manufacturers focus on optimizing their equipment to compare with competitors only at this level of operation.  So what ends up happening, we have a lot of dehumidifiers that look like this picture, which all compete to be energy efficient and effective at the AHAM level of 80°F and 60% relative humidity.  This relative humidity is just at the edge of guidelines suggested by the EPA government agency (Ever eat minimum quality government cheese?) and it’s an unrealistic temperature.  These are the same guidelines adapted by Energy Star as well as most building codes.


Coincidentally, around the same time period, technology and practices evolved for building air tight, well insulated homes.  The result is that today, we are seeing increased cases of allergies and asthma triggered by poor indoor air quality.  As a reaction, consumers are educating themselves and finding solutions for their indoor air quality.  Now let’s take it to the next level, beyond what you can find on a government website!

Keeping comfortable humidity levels in the living space of your home is dependent on relative humidity, the percent of water (which by the way, you can feel) in the air before the air becomes 100% saturated and rains, snows or condenses.  But that 60% relative humidity is the bare minimum for the living spaces only.

To keep infestations, dust mite and mold populations down you need to be aware of Absolute Humidity and Dew Point.  Relative humidity will tell you if you feel humid.  Absolute Humidity is found by weight, how much water is actually in the air regardless of temperature or relative humidity.  (Dew point is measured in grains of water per pound of air.  A grain is 1/7000 of a pound.  This tells you the mass of water found in a sample of air.)  Dew Point, directly related to absolute humidity, is the temperature at which water vapor will condense.

When humid outside air enters your home, its dew point does not change.  Even as the air warms or cools inside your home, the Absolute Humidity and Dew Point remain constant.  Usually what happens inside your home is a change in temperature which changes relative humidity.  As cool winter  air warms, relative humidity drops.  As warm summer air cools, relative humidity rises… but dew point stays the same.

If dew point is 60°F (which is pretty common), a 40°F glass of cold water will form dew on the outside as water vapor from the air condenses.

Now let’s move to your crawlspace.  Dew point is still 60°F, but the water pipes are 55°F and the walls are 60°F.  The pipes and the walls will be covered with condensation.  It may feel dry in your living areas, but in the cooler area under your home moisture will accumulate.  Moisture from the ground will also enter your crawlspace via capillary action.  This is when water naturally seeps from a moist area to a dry area through your crawlspace walls.  This moisture from the walls and ground will evaporate into the air inside your crawlspace.  And humid air, like warm air, always rises.  It will rise up from your crawlspace and circulate throughout your home.


Appliance dehumidifiers, like the unit above were built according to EPA criteria and only work in the warmer, less humid areas of your home.  EPA and Energy Star do not have hard numbers or specific guidance for crawlspace humidity.  And many homes, built to code, use ineffective techniques for adequately controlling humidity.  A handful of forward thinking local and regional agencies are just recently starting to form recommendations and practices on truly effective crawlspace construction techniques as well as dehumidification equipment.

OscarAir is one of these forward thinking organizations.  We have performed our own testing and research.  We have developed an easy to follow FREE REPORT on Crawl Space Dehumidifier Selection that includes 7 things you should know before buying any crawlspace dehumidifer.  Furthermore, we have developed efficient and effective crawlspace dehumidifiers with a performance guarantee.  Sign up to receive the FREE REPORT and call OscarAir to have a specialist calculate and specify the correct size and number of dehumidifiers to use in your crawlspace.

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