In parts 2 & 3 of this series of blogs, we have talked about Filtration (linemen) and Ventilation & Purification (line-backers).  In today’s blog—we will talk about our secondary— Humidity Control.  Just like a good football team counts on safeties to keep the ball out of the end-zone, Humidity Control can go a long way towards preventing infectious disease transmission AND help you be more comfortable too.

The Importance of Controlling Humidity

As HVAC professionals, we have preached humidity control in order to make comfort possible.  It makes sense if we think about it:  consider the impact of humidity on comfort when we think about a “cool 80 degrees” in Arizona versus a “muggy 80” in Florida.  It’s not the heat, it’s the humidity, right?

But the health benefits of humidity control go way beyond comfort!   The American Society of Heating, Refrigeration & Air-Conditioning Engineers (ASHRAE) recommends humidity be maintained at or below 65%, while the EPA recommends maintaining indoor relative humidity between 30-60% to reduce mold growth.

Also, we can see in our handy-dandy ASHRAE 52.2 chart—where mold and microbial growth occurs—or more importantly where it doesn’t occur—between 40-60% RH!

Image #11

But what does all of that have to do with human health?  We all know the signs of lack of humidity—cracked skin, dry eyes, and even bloody noses.  But according to a study by Harvard Medical School and Dr. Stephanie Taylor

Humidity Blog 4

Dry inhaled air causes increased susceptibility to infections and increased wheezing from allergic disease.  Further, numerous studies demonstrated that when indoor RH is between 40-60%

  • Respiratory & GI infection rates were the lowest
  • Decreased Infections—including influenza
  • Fewer allergies
  • Improved hydration
  • Improved wound healing
  • Increased work performance

Influenza Blog 4

Most infectious bacteria and viruses are tiny and float in the air for a long time, from 41-hours up to 21 days.  However, with the moisture between–say it with me now– 40-60% RH– many of the viruses can be captured by the moisture in the air, drop to the surface, and then we can disinfect.

Please understand, that does not mean ALL viruses can be rounded up and killed in this way—in the studies, people still got sick, just at a much lower rate.  For all of those reasons our final IAQ TIP Consider installing WHOLE HOME humidifiers and dehumidifiers to your system—Low & High humidity control is important for wellness, health & comfort!

At the end of the day—isn’t that what we all are hoping for?


2016 ASHRAE HVAC Systems and Equipment Handbook
EPA Residential Air Cleaners A Technical Summary
2018 EPA “Guide to Air Cleaners in the Home”:
EPA EnergyStar Guide to Efficient Heating & Cooling:
US Department of Energy:
Indoor Environmental Quality:  CDC:
AHRI:  Humidity & Occupants:
“Optimize Occupant Health, Building Energy Performance,” Stephanie Taylor, M.D. Harvard Medical School
Aprilaire Presentation on Ventilation
Honeywell Presentation on Humidity Control

Written by Bill Yeakel

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