July, 2009
News in Brief
Inspection News and Views from the American Society of Home Inspectors

The Mays Move Beyond Mold


“Jeff May’s Healthy Home Tips: A Workbook for Detecting, Diagnosing & Eliminating Pesky Pests, Stinky Stenches, Musty Mold, and Other Aggravating Home Problems,” by  Jeffrey C. May and Connie L. May, is now available.

Mold, mildew and other airborne contaminants lurk even in the cleanest houses, causing serious health problems and damaging your home. Drawing from their expertise and previous books — “My House is Killing Me!,” “My Office is Killing Me!” and “The Mold Survival Guide” — the Mays have created a step-by-step process that can be customized to your unique situation or to help others, whether shopping for property or trying to figure out why you sneeze every time you set foot in the basement.

Throughout, this winning team serves up advice and anecdotes with warmth and humor, in a give-and-take that only professional and personal experience can yield.Published by Johns Hopkins University Press, 2008, the book is available on www.mayindoorair.com.

May also publishes bulletins on indoor air quality. One is reprinted here with permission. If you would like to receive these bulletins, e-mail him at jeffrey.may@comcast.net.

IAQ IQ: Bulletin 9 – “IAQ Dementia”

In the next several bulletins, we will be discussing different pieces of mechanical and cleaning equipment designed to improve IAQ, but which don’t always live up to the hype. Since home inspectors are responsible for reporting on the visible conditions of installed equipment, we’ll start with components of air conveyance systems.

It’s worth repeating that the most important function of a filter is to keep the blower cabinet and air conditioning coil free of all dust and biodegradable debris. A secondary function of filtration is to clean the house air (most of the dust in the air contains skin scales from people and particles captured in carpet and fleecy-cushion dust that becomes aerosolized when disturbed). We’ve said in earlier bulletins that anyone should use a MERV 8 pleated media filter; people with allergies or asthma should use a MERV 11. A HEPA filter is MERV 18, but is not available for in-line, residential use because such a filter creates too much static pressure for the blower. There are, however, by-pass HEPA filters available for installation on central heating and cooling systems. In theory, a by-pass HEPA filter may seem like a good idea because it cleans absolutely all the air that passes through it; however, approximately 90 percent of the air by-passes the by-pass. So a by-pass filter is like a very expensive condom with a hole in it: not great protection!

Another “innovation” in filtration is the so-called turbulent flow precipitator, which consists of several media filters stacked in a holder, with the air passing sequentially, over rather than through, the filters.

Supposedly, multiple passes of air over the pleats causes the air to rotate and dust to deposit on the filter surfaces. In reality, many particles survive the multiple passes and remain suspended and distributed by the mechanical system.

Electronic filters are very efficient in theory, but they lose their filtering capacity as they get dusty. Since homeowners rarely clean such filters frequently enough (monthly), the filters end up being useless in most homes. Similarly, electrostatic filters are rarely cleaned enough and can never be cleaned thoroughly enough, and so, are a waste of money.

Ultra-violet (UV) lights are another innovation, which supposedly keeps the mechanical system free of microbes. UV light has been used for decades to disinfect air, and it does so successfully; however, the pivotal Canadian study that stated that UV lights would improve the health of millions of allergy sufferers was flawed and thus the conclusion invalid. If any of you are interested in this study, I’ll be happy to provide a one-page critique. UV light is great for tanning, but useless for cleaning up a contaminated fan coil or duct system.

Moving on to silver-lined ducts — such ducts are no silver lining! Although steel coated with a low concentration of silver may restrict the growth of microorganisms on the metal, in real duct systems, microbial growth occurs on the dust, not necessarily in contact with the metal. That said, I’d certainly prefer to see metal ducts in an air conveyance system because they are smooth and can be cleaned, whereas flexible ducts have ridges that collect dust and, once contaminated with microbial growth, have to be replaced.

Other solutions to tight buildings and damp buildings include the installation of air-to-air heat exchangers. Air-to-air heat exchangers, also called energy recovery ventilation (ERV) or heat recovery ventilation (HRV), consist of devices that continuously exhaust stale house air and bring in fresh outdoor air. There are a few problems with these units. First, they are not installed with a pre-filter to keep the intake duct clean by preventing the build-up of outdoor pollen, mold, other plant materials and insects. Second, the built-in filtration within every unit that I have seen was inadequate, allowing dust to build up on the heat exchanger, blower and interior of the unit. Whether in winter or summer, hotter air meets cooler air within the heat exchanger, and condensation may occur. And most units I’ve seen do not have any accommodation for drainage, even when the exhausted air came from bathrooms and hot-tub rooms. Moisture and dust and voila! Microbial growth! Some of the models I’ve seen even had exposed, fibrous insulation that had become wet from condensation and then contaminated with mold and bacterial growth.

If a client has an air-to-air heat exchanger, make sure that he or she cleans the interior regularly (the best models have readily removed heat exchangers) and maintains it dust-free, and that the client replaces or cleans the filters four times a year. A pre-filter should also be added near the outdoor intake. Unfortunately, the filters within such units should be a minimum of MERV 8, but with only one exception that I know of (VanEE), none of the manufacturers make blowers that have the capacity to overcome the static pressure created by such filtration. The best solution to the filtration problem is to eliminate the two internal filters and use in-line external media filters with at least a MERV 8 rating. The filter for the incoming fresh air should be close to the intake grill, and the filter for the house-air inlet close to the HRV. One last caution: Venmar recently had a recall of 75,000 of its air-to-air heat exchanger because the blowers may overheat; four have caused fires.

Several manufacturers are selling “smart” basement exhaust fans that supposedly perform like dehumidifiers. These sophisticated toys sell for more than $1,000 installed. All I can do is ask: “When the relative humidity outside is 80 percent, how can a fan “dry” the air and basement???“ Yet another example of “IAQ Dementia!”

©2007 Jeffrey C. May, www.mayindoorair.com