Indoor Air Quality

Indoor Air Quality (IAQ)


Some of the primary concerns revolving around IAQ presented to this author are: "Is there mold?", or "I feel stuffy!" These are issues covering Particulate (solid) or Volatile Organic Compounds (VOCs, gas). Some qualities are entirely separate from each of these issues, and involve forced mechanical motion and water content (humidity).

  1. Airborne Particulates 
    in order of decreasing size
  2. Volatile Organic Compounds
  3. Airflow Dynamics


We love plants, or we should, because they provide nutrition, they convert our gaseous exhaust (corbon dioxide, or more commonly CO2) into Oxygen that we consume continuously, and they provide beauty in the form of shapes, colors, etc. However, in order to propagate, they must pollinate. And pollinate they do, right into our very noses. Pollen, the small "seedy" part of plant anatomy, is either scattered about by pollinators (bees and other insects) in a long-term fashion, or by wind in a short-term fashion (sometimes only lasting a week or two per year). The latter is a cause of aggravation and suffering for many individuals who on an ongoing basis suffer from congestion, sinusitis, and a reduced ability to breathe. Aside from the destruction of all plant life on the planet (a course of action Not recommended), the only alternative is to be indoors. Simply being inside a shelter one is protected from the seasonal onslaught of innumerable and varied kinds of airborne bodies intended to make plants propagate, and their indoor concentration is generally lower than outdoors due to the protection from meandering air currents. For a reduced presence, one can use a stand-alone air filter unit, which will reduce the particulate concentration in one or more rooms. When that shelter is additionally equipped with a central air mover and distribution system, the indoor concentration is bound to be several magnitudes lower than outdoors. Unfortunately, everyone does not have such equipment, so some are left to their own cognizance of when the pollen season is expected, for certain of the most irritating pollen producers such as ragweed, and to seek appropriate protection indoors. Size-wise these are the heaviest, and produce a layer of fine colored "dust" on horizontal syrfaces, until a breeze again lifts them up. Being organic, they form an excellent and diverse food base for bugs small enough to benefit from it.


Molds are necessary agents of recycling and exist everywhere. They slowly devour most surfaces they come in contact with, reducing them to their basic chemical constituents. If the surface is inert, as in metal, then they may simply feed off the dirt on its surface. Particularly attractive to mold are surfaces containing cellulose. Cellulose is the main component of wood and its derivatives, such as paper. Cellulose is also a structural rearrangement of simple sugars that gives the assembly great structural strength, and great nutritional value when decomposing due to excessive water content, rendering it easily digestible by mold.

Molds thrive particularly well on moist surfaces. Modern dwellings are outfitted with a plumbing infrastructure that penetrates many structural walls. Any leak (however small) provides the proper environment for mold to colonize. Inattention to the leak(s) for greater than 24 hours, promotes conditions appropriate for rapid growth (amplification). Allowing ambient moisture content to rise above about 65% will provide similar favorable conditions for growth. Continued favorable conditions can allow sequentially more aggressive species (whose frequency of occurrence indoors is generally very low) to manifest themselves, possibly feeding off the dead mold colonies they replace. While many species are allergenic, some species are toxigenic, mutagenic, and carcinogenic. When molds colonize a favorable surface they produce a mycelia that penetrates the surface, in some respects similar to a plant's root system. They also produce outcroppings (similar to plant's trunks and branches) that produce spores. When agitated, or physically or chemically stressed, these spores easily become airborne. You should easily begin to see that simple surface treatment of mold infestation on a porous surface is a cheap and incomplete solution, when the causative factor is not addressed.

in a properly controlled environment, airborne mold spores, available continuously, settle out on clean surfaces and begin to form a microscopic layer of biota. Although inert, because the humidity does not promote growth, they are noneheless organic, and can form a food base for bugs small enough to benefit from it.

Animal and Human Dander

We itch, and scratch ourselves, so do animals. In the process copious amounts of hair and skin cells are shed. Over time these droppings congregate into "tumbleweeds" that locate themselves near wall-to-floor intersections. Over additional time, these acquire names, and seem to follow us around, screaming "It's time to cleeean!" Those who have carpeting have a superficial cover-up. The shed material collects within the matting of the carpet, and gradually provides a dirt layer to complement the carpet matting "forest." As individuals walk over carpeting, each footstep temporarily crushes the matting and forces localized air currents that liberate some of the accumulated dust for us to inhale. We have come full circle!

The idea is not to scratch . . . so try to teach that to a dog, cat, or other animal. But really, the cure is a regular cleaning regimen. It does not need to be extreme, but it needs to be regular and address the areas that are the most prolific sites of collection. Those areas exist underneath every piece of furniture, especially those that get moved the least, and even more especially those whose function causes them to have a recurring forced flow of air around them, such as a refrigerator due to its cooling coil operation, or baseboard radiators. The author has many times come to visit and found copious amounts of dust under various pieces of furniture to such a degree, that he is left wondering how many years (decades?) it had been since some of those areas saw a vacuum cleaner hose. The author has seen some refrigerator bottoms that appeared to be repositories of a dead cat. Being organic, this is part of the food base for small bugs, such as dust mites.

Dust-mite Debris and . . . Dust

Dust-mites are aptly named because they are mites that live on and in dirt, because it's organic (as from the paragraphs above). They eat it and produce microscopic droppings that are a potent allergen. We humans are not keen on eating bug droppings, but we do it a lot, ignorantly, because we do not know where the dirt is, and what lurks on and within it. The dirt gets into our sinuses and lungs by a process akin to that from a leaf blower. Previously described herein, at the risk of being redundant, allowing dirt to collect, and then stepping on it, causes it to go airborne. Some have stated that "we are what we eat", and we submit that "we eat what we do not pay attention to".

It may be a no-brainer, but more dirt = more problems. Dust mites are opportunistic. Present everywhere, their available concentration cycles with the concentration of organic debris, which can be vegetative remains, degenerative remains , or carnivorous remains, as described above.

Along with dust, viable (with life) or not, comes a cleaning regimen. A vacuum cleaner is a wonderful thing. It collects dust for easy disposal. However, most vacuum cleaners have a colection efficiency limit of about 5 to 10 microns (millionths of a meter), which is about the same efficiency of our noses. Thus they trap the visible and leave most of the invisible go though the filter and become evenly distributed. Many central air systems have a filter that is even worse, having a trapping efficiency of a 1/4 inch or greater. I have never seen a pollen or mold spore look at me while I was looking at it, because most are too small for the naked eye. Such coarse filters are for machine protection. Isn't our health more valuable? High Efficiency Particulate Air (HEPA) filter equipped vacuum cleaners presently may cost as little as $100, while improved filtration for a central air machine may cost $4. But even with filters, they need to be cleaned or replaced, in order for them to function as intended. With centrail air systems, a more pressing problem arises, because a poor filter allows easy accumulation of dirt within the cooling coils, the air mover blades, and the subsequent air ducts. When this dirt becomes sufficient, it becomes a haven for the same biota previously discussed, and propagation of it through the entire home each time the machine operates. Considering that the air mover causes air turbulence (great for heat transfer), should alert those affected that if they see particulate emissions from the air duct openings (made airborne by the turbulence), there is an immediate and dire need for cleaning the internals, which might have been prevented by a better filter.


Bacteria, as most other particulates are ever-present. They, like mold, appreciate surfaces that have been made wet from leaks. Their food base requirements vary depending on the genus (similar with molds), and their propensity to cause trouble is mainly evindenced by leaks that go untended, maybe because "it's the landlord's problem," or because "it's somebody else's job." They may produce aromatics that are telltale, or not, depending on the many variables necessary to foster masive growth spurts. As with Molds, These growth spurts are known as "Amplification." Since the factors favoring amplification may not be constant, the cyclic checmical and physical stresses forced onto the opportunistic biota forces them to produce airborne spores, or cast off portions of their structure.

Biota Size perspective

Identification of problem areas associated with viable particulates should be focused oon the cause, not the effect. A leak or high moisture is the cause. Excessive mold, dust-mites, or bacteria is the effect. Removing the mold and leaving the cause will allow the mold to reoccur, similarly with bacteria.


Some of the smallest particulates, viruses have a very limited lifetime outside a host. Their existence, however, can be lengthened somewhat if they find a receptive surface rich in nutrients. Surfaces rich in mold, dust-mites, and / or bacteria, may provide such a surface. The solution centers, as before, on a regular cleaning regimen.

Microbial VOCs

Organics produce gas. They do so during digestion, and for those trapped into the mindset that gas is bad, you may be in for a rude awakening if you get sick, because unless you produce gas, you're not leaving the hospital. Bacteria, and mold are also gas producers. Some gas is produced as a byproduct of normal digestion, while some of the gas is produced as an offensive or protective mechanism if the colony chemically senses some intruder that may reduce its food base. This latter category can be hazard to humans, when in sufficient quantity. The variety of aromatics may resemble a musty smell, or one of rotten eggs, or one of many other varieties. When one enters a home, or goes from one portion to another (as from the upstairs to the basement, or from living spaces to a garage), there should not be any identifiable or offensive aromatics.

Non-microbial VOCs

VOCs are aromatic or out-gas byproducts (dry-out evaporation) of many chemicals in our "modern" environment. Paint for instance, is a liquid that is applied to surfaces for a certain color rendition. The emulsion within the paint fluid coats the surface it is applied to, while the liquid evaporates. The liquid is a mixture of many volatile compounds that can be biological irritants. Their dryout can take as much as several weeks, but can be accelerated by a bake-out.

Engineered woods, plywood and particleboard in particular, are made of wood sheets or pieces that are glued together. The glues use a formaldehyde base that evaporates and irritates lungs, throat, and other organs.

Plastics are usually produced with phthalates (plasticizers) to give them "that soft feel". Ever smell that "new car smell?" It is in part due to the phthalates evaporating, which also coat the inside of the windshield and cause a slightly opaque coating. Plasticizers can be as much as 50% of the material content of plastics. These evaporate and become biological irritants (try at home: place water in a polyethylene bottle and keep in storage for 4-6 months, then taste the water and its associated "plastic" flavor. (Some plastic glasses can impart that plasticflavor in a matter of minutes!)). Plastics are encountered in furniture, kitchen utensils, office supplies, carpeting, clothing, and just about everything that can be manufactured. To add insult to injury, many carpets are treated with fungicides / pesticides, which volatilize into the indoor environment. In a new home, the out-gassing becomes a default contaminant of the breathable environment for many years, And if the owners immediately occupy the structure upon completion, they risk long term effects that last well beyond the brief break-in or getting-to-know-you time in a new residence.

An engineered source of VOC pollutants is the hot water boiler. As it heats the water, the elevated temperatures make any VOC more volatile. When the water is sprayed in the process of washing dishes, clothes, or showering / bathing, the VOCs become airborne. Water acquires these VOCs from ground contamination and runoffs, as well as water treatment processes. Chlorine and Fluorine, common water treatment chemicals, also become airborne, and irritate. While many domestic water supplies are reasonably clean, even trace amounts of certain VOCs are sufficient to introduce biological influence. Whether public or private, a domestic water supply is well worth sampling on a regular basis, yearly or so. If certain unwanted water contaminants are identified, then filtration or sterilization can be introduced.

In a public water supply system, Chlorine is a major concern. While doing its duty in killing undesired microbes, it is not needed for showering. Ever get eye irritation from hot water while showering? Thank the Chlorine. Coincidentally, in the interest of conservation there are showerheads available that produce a very efficient atomization of the water flow at a minimal flow rate. While good for conservation, this is also most efficient for volatilizing Chlorine and other aromatic compounds in the water supply. A good filter (usually an activated charcoal unit, changed regularly) will easily reduce / remove the chemical content. Usage of a moderate flow shower head that does not finely atomize water droplets will also be helpful.

VOC source materials

In a tight dwelling, the buildup of pollutants can be dramatically quick. Since a VOC source material may be solid, liquid, or gas (if VOCs are entrained in the fresh air supply), their removal can be a filtration issue (if they are sought to be removed BEFORE they enter the living environment), or it can be a neutralizing / removal issue (if they are sought to be removed AFTER they enter the living space). Access to air / liquid entry paths will most likely determine which method is employed.

In a new home, there are many construction materials that emit copious amounts of VOC out-gas. Exterior walls (essentially being airtight barriers) enclose a few additional sources. While some advocate a home bake-outto substantially reduce VOC emissions (because the present norm is to occupy a house immediately upon completion), the positioning of certain materials beyond moisture barriers, will keep them available as long-term low-level sources of VOCs. When a home bake-out is considered, it is conducted immediately after construction, by raising the internal temperature to a high level (85 degrees Fahrenheit / 30 degrees Celsius), and then rapidly ventilating the structure. The cycle is repeated several times, forcing enhanced out-gassing and air volume purging.

There should be NO VOC content in a healthy environment, other than NATURAL emissions from such things as aromatic flowers, wood, etc.

Combustion Products

A typical domestic setting is provided with a heat source that feeds a forced air or hydronic system. Most often, the furnace uses indoor air to feed the fire. When the furnace initially fires, before the stack-effect (updraft) is established, there is an initial surge of partially burned combustion products in all directions. This will produce a "smell" of gas or oil within the immediate living space, reminiscent of a leaky exhaust duct. As the updraft is developed, those combustion products are sucked back into the furnace and exhausted outdoors. If there are competing sources of suction elsewhere, such as a clothes dryer, or a bathroom or kitchen fan, those partially burned combustion products can migrate elsewhere throughout the home. During this process, more air needs to be available to feed the fire. A whole-house vacuum (or negative pressure when compared to outdoors) is established, dragging outdoor air in through window, door, and boundary wall imperfections. Standing near any of these will create a sensation of a cold draft. This describes the operation of an Open Combustion heat source. A conventional fireplace also fits this description. 

This is both good and bad.

Static Conditions without air movement Open Combustion with a fire lit Open Combustion with a fire lit and a vent fan on - ASPHYXIATION HAZARD

From an air quality perspective this is very good, as human and animal life is Oxygen dependent, requiring a continuous fresh supply of air. It also can be very bad if there are sources of pollution outdoors, because these would also enter the living environment.

From a comfort standpoint, this uncontrolled air entry is bad because it generally involves very low humidity levels. Personal comfort, as well as reduction in microbial growth potential, is accomplished with humidity levels between 40 - 60%. Wintertime climates can produce humidity levels well below 20%. This will produce problems keeping a healthy skin tone, as well as breathing, and eye irritation problems.

The solution does NOT include making doors and windows tighter.

When a furnace and a wood fireplace are both provided, they will compete for the same supply of fresh air.Trying to start a fire in the fireplace while the furnace is ignited might prevent establishing the updraft in the fireplace, bringing all the combustion products indoors.

If the fireplace is not in use, and its stack is near the furnace's, the exhaust can be recycled back indoors by the negative pressure, unless the fireplace damper is very-tightly fitting (which they seldom are), with serious consequences.

A partial remedy to the above is to provide an external source of air for furnace (or fireplace) combustion. This concept is then known as Sealed Combustion. Doing so will eliminate the indoor vacuum, and will allow the establishing of a more controlled moisture level, reducing many related complaints. However, it will present other challenges relating to a fresh supply of air, as removing the indoor vacuum will allow indoor-generated pollutants to build up, eventually reducing the comfort level.

Sealed Combustion with fire lit Sealed Combustion with fire lit and vent fan on

One remedy; is to use plants to provide a fresh supply of Oxygen and moisture, as well as remove VOC buildup. Although forced ventilation is many times faster in providing air exchange, plants do it without noise, without costly installation, and with pleasing NATURAL settings and aromas. If plants are used, the soil needs to be replaced occasionally, and it should not be kept thoroughly wet, to preclude mold colonization. An inexpensive soil moisture indicator will be quite useful in this respect.

There should be NO Combustion Products in a healthy environment.

Air-flow Dynamics

It is not uncommon to find an expensive mansion with lots of gadgetry and controls, and during times when the heating or cooling system is not required, there is a minimum of air motion. Confort then is only possible with a local fan to maintain some air motion. Any central air circulation system should be set up to maintain a minimum of airflow at all times. This has the added benefit that any dust generated by normal activities will be routed to filtration and captured, providing for cleaner air to breathe.

During inclement weather, whether hot or cold, we spend much of our time indoor. Typically this does Not include air exchange with the outdoor environment, except when doors are used to exit or enter the structure. One alternative is a Heat Recovery Ventilator or Heat Recovery Air Exchanger. This device exchanges air with the outdoor environment, causing the two separate air paths to flow through a heat exchanger, allowing for reduction of heat loss or gain.