Relative Humidity and Why It Matters

You can control a key variable associated with proper air quality in your home by maintaining relative humidity levels.  

Anyone who has watched the Weather ChannelEverybody’s heard the weather report and grasp the concept that excess humidity is muggy and low humidity is dry. New Englander’s know that basements should have a dehumidifier to lower the humidity. Physicians recommend humidifiers to increase humidity in the winter when its’ dry or to relieve coughing and congestion. So what’s the big deal with humidity in the home and what’s the ideal range? For indoor air quality purposes the ideal range is between 35-45% relative humidity.

Let me try to clear the air regarding some of the basic terms which are not interchangeable.

Relative humidity is a ratio of the amount of water in the air compared with the amount of water the air can hold at a given temperature. Air’s capacity to hold water vapor increases with increasing temperature. Warmer air can hold more vapor than colder air. This is why 60% relative humidity at a temperature of 95F feels muggier than 60% humidity at a temperature of 40F.

Dew point is an absolute measure of the amount of water in the air. It is the temperature at which the air, at the current amount of water vapor, will be 100% saturated. Reduce the temperature any further and water will condense out and form dew or fog, hence the dew point. In fact, you'll often see fog forming even before you reach that point.

Mold spores and dust mites will increase exponentially when the relative humidity exceeds 60% for a sustained period of time. A typical basement without a dehumidifier will read between 65-75% relative humidity during summer months and between 45-60% during winter months.

Most people will know when it’s dry or below 20% RH or muggy when above 70%. However while the average person will notice a five degree change in temperature they are not able to notice changes between 20-70% relative humidity. This is why monitoring the relative humidity in your home or basement is so important, yet few people do. 

Relative humidity is measured using a hygrometer. You will want to set your dehumidifier to around 35% or continuous mode to ensure the relative humidity at the opposite end does not exceed 55%. Don’t rely soley on the relative humidity reading on your dehumidifier. These displays are notorious for being inaccurate. We recommend a quality digital hygrometer like the Extech brand sold through Professional Equipment for around $45. 

Ten Things You Can Do On A Weekend To Improve The Air Quality In Your Home

1) Cap your sump pit. A properly capped sump pit will reduce radon gas, which is the second leading  cause of lung cancer in the United States. An added bonus: you deter the mice and rats from an unnecessary watering hole.

2) Change your air filters. Clean air filters will reduce the amount of harmful debris and particulates in the air.

3) HEPA Vac your house. Vacuuming your home with a functional HEPA filter vacuum containing a bag that is no more than halfway full will reduce organic matter (skin cells, dust, dirt, debris) leading to mold growth and dust mites. Make sure to use the correct vacuum attachment for your flooring. If you outsource your home cleaning, provide your housekeeper with a HEPA vacuum only to be used in your home to prevent unnecessary cross contamination of unwanted allergens.

4) Disinfect your bathroom. A proper disinfectant will kill off the nasty bacteria, viruses and fungi which thrive in your damp, moisture-rich bathroom. Let the solution sit for an appropriate dwell time of at least 5 minutes.

5) Run your dehumidifier and measure its effectiveness (especially in the basement). The typical dehumidifier at the hardware store typically lasts for 3-5 years. You can monitor the effectiveness of a dehumidifier with a hygrometer. The ideal range for humidity in the basement is below 45% (a warning: this is is tough to achieve unless your basement is drained with a sump pump or existing plumbing line). Newer dehumidifiers have a convenient hygrometer already built in so you can set the appliance to 40%; when the moisture in the air rises above 40%, the dehumidifier kicks on and consequently turns off when the air saturation dips below 40%.

6) Safely dispose of unwanted paint cans and other volatiles. The pyramid of toxic fumes in your garage or basement can off gas into living areas and contaminate the air quality with excess volatile organic compounds (VOCs). When in doubt, safely throw it out.

7) Run a high quality room air purifier in your bedroom and living rooms. Most purifiers that we test don’t live up to what the manufacture states. However, a few really do improve air quality. We like the IQAir (www.iqair.com) and Austin Air (www.austinair.com) brand purifiers based on before and after testing. These brands are top picks with our clients who want the best possible air quality in their home. www.allergybuyersclub.com is an excellent resource to compare products and read independent reviews.

8) Open the windows. Encourage fresh air whenever possible. Take a look to see if there is an opportunity to install a standalone ventilation system like EZ Breathe (www.ezbreathe) in your basement or if you can retrofit your AC unit with a recovery system. Also make it a habit of running the shower exhaust fan for at least 30 minutes after bathing. The exhaust should be firmly secured through the exterior or soffit vents.

9) Declutter. Not only is it satisfying to lighten your load, but you’re also improving airflow and reducing the overall surface area in your home for dusts and allergens to cling on to. The closet crammed with porous clothing or that nook under the stairwell packed full with cardboard boxes create a most favorable environment for molds, dust mites and odors.

10) Encase your mattress. Even if you doubt that your mattress is 50 pounds heavier with dust mite matter, it’s still a good idea to protect your body from unwanted allergens and your mattress from excess sweat. Have you looked at the water stains on your pillow or mattress pad lately?