“What? I’m just the HVAC contractor. I didn’t build the damned house,” Jim Brown thought as he read the court order.

The cooling system he installed last year was perfectly sized to handle the load that he had meticulously calculated. This year he found himself embroiled in a lawsuit. Moisture problems in the home resulted in mold growth that allegedly caused the illnesses of the entire Johnston family.

Sound far-fetched? HVAC contractors are being named more often in the latest legal craze — indoor air quality (IAQ) liability.

In the modern urban setting, most individuals spend about 80% of their time indoors. That’s why good IAQ is critical to good health.

What’s Good/Bad IAQ?

According to the EPA (Environmental Protection Agency), indoor air pollution is ranked as the highest risk to human health among all types of environmental problems. Studies conducted by the EPA indicate that levels of indoor pollutants may be two to five times higher, and occasionally more than 100 times higher, than outdoor levels.

Acceptable IAQ is considered to be air in which there are no known contaminants at harmful concentrations. Sources contributing to indoor air contamination include ventilation and air conditioning systems, building materials, furnishings, combustion of gas for heating and cooking, smoking, cleaning agents, and humans.

Causes of Poor IAQ

The three most frequent causes of poor IAQ are (1) inadequate design and/or maintenance of the heating, ventilation, and air-conditioning (HVAC) system, (2) a shortage of fresh air, and (3) lack of humidity control.

The quality of air inside the home encompasses much more than how warm or cool it is. Designing a proper system means also taking into consideration lifestyle choices in addition to proper load calculations. For example, occupants’ general health, cooking, smoking, exercising, cleaning habits, having pets and/or plants, all play a major part in the condition of a home's indoor air quality.

One of the most important aspects of good indoor air quality is proper ventilation. Residential ventilation traditionally wasn’t a major concern because it was felt that between operable windows and envelope leakage, people were getting enough air. In the quarter century since the first oil shock, however, houses have become much more energy efficient.

Because tighter, better insulated homes were built in response to the energy crisis in the 1970s, natural ventilation has been virtually eliminated and many airborne contaminants were trapped in homes. At the same time, the kinds of materials used and functions in houses were changing in response to people's needs. Plus, people were becoming more environmentally conscious not only about the resources they were consuming but about the environment in which they lived.

In a nutshell, tightly constructed homes decrease the amount of fresh air that enters a structure, creating an unhealthy environment.

Tight home construction may mean less airborne dirt and dust can infiltrate the structure from outside (assuming the duct system is tight). However, it also means whatever dirt, dust, grease, pollen, and mold spores exist within the home are often recirculated.

HVAC products that address filtration of air, ventilation and fresh air, and humidity can address many contaminant problems. Here’s a run-down on a few of those available:

Filtration Systems

A typical furnace filter only removes 10 to 15% of contaminants. An air cleaner can remove up to 95% of airborne particles. Several types of air cleaners are available today, each having various advantages.

Electronic - Media - Electrostatic

One of the most efficient air cleaning products for residential home systems today is the electronic air cleaner (EAC). It can effectively clean particle pollutants from 0.3 to 3 microns in size. However, to enhance the removal of airborne pollutants, all electronic air cleaners must be properly maintained on a regular basis.

Once an EAC is at its holding capacity, airborne particles will begin to blow by and will recirculate into the living space. Cleaning the cells of the electronic air cleaner may be required every two to three months or even more often, depending on the home's situation. For example, high infiltration, cooking, dust, or tobacco smoke may lead a contractor to suggest more frequent cleaning of the air filtration system.

Most manufacturers provide standard or optional service lights that tell you when EAC maintenance is needed.

Media air cleaners generally consist of a pleated material with a surface area many times greater than that of a standard furnace filter. Upon initial filtration, media filters can clean up to as much as 80%
of particle pollutants ranging in size from one to three microns and as low as 2% of particle pollutants from 0.3 to 1 micron in size. As the material loads up with dust and dirt, it becomes more efficient, filtering even finer dust and particulate matter.

These filters require periodic replacement. Not replacing these filters on a regular basis can lead to reduced air flow, which affects comfort. This also creates added stress on the unit's operation, which in turn has an effect on the reliability of the entire system. Since the unit must work harder and longer to pull the required air flow into the system, potentially higher utility costs can also result.

Electrostatic air cleaners: As dirt, dust, and other particles move across a series of mesh elements (usually plastic), the static electricity caused by this friction charges the particles and traps them inside the element. Maintenance is accomplished by removing and washing the filter. The effectiveness of this type of air cleaner varies by brand.

Regardless of which high-efficiency filtration system you choose, it only cleans the air when the blower unit of the heating equipment is operating. Running the blower continuously on the central air system will help clean the air in a home more effectively and efficiently than if the unit is cycled with a call for heating or cooling.

Ventilation Products

Continuous, whole-house ventilation can be provided by heat or energy recovery ventilators (HRVs or ERVs).

Both reduce indoor air pollution by exhausting stale contaminated air and introducing fresh air from outdoors, much like an opening a window. Unfortunately, an open window isn't always practical in the heating season, doesn't provide control over the entering air, makes humidity control next to impossible, and it wastes energy. Following is a comparison:

Heat recovery ventilators (HRVs). Mechanically, an HRV is a combination of fans, controls, and heat recovery elements that exhaust stale air from the home, bring fresh air in from outdoors, and transfer heat energy from one airstream to the other. HRVs are usually recommended for colder climates with longer heating seasons.

Energy recovery ventilators (ERVs). Similar in operation to HRVs, ERVs are capable of reducing the moisture content of the fresh incoming air. As a result, they can reduce the load on the air conditioning system during summer operation. ERVs are preferred for warmer, humid climates with longer cooling seasons. For successful winter operation, ERVs must be equipped with a suitable defrost mechanism.

Indoor Humidity: Good and Bad

Humidity is a necessary component of indoor comfort. However, too much of it makes us feel sticky and hot on a sultry summer day and can cause mold and mildew to grow in kitchens or bathrooms. Not enough humidity in the winter creates an assortment of other problems. The simple act of turning up the thermostat during winter months dries out the structure. That's because warm, dry air acts like a giant sponge that soaks up moisture from everything it touches.

The unpleasant results: dry skin, chapped lips, sore throats, and clogged sinuses. Hardwood floors separate at the seams. Woodwork and furniture shrink, warp and crack. The piano goes out of tune. Wallpaper peels at the edges.

Even if a home is tightly constructed it can lose humidity. Extremely dry, cold outside air can quickly drop indoor relative humidity by 10 or 20% (cold winter air doesn't hold much moisture). Prolonged periods of dryness in a structure can begin to dry and shrink framing, increasing gaps where outside air can infiltrate the walls and cause drafts and higher energy consumption.

What is a proper humidity level? Between 35 and 50% is considered ideal for a comfortable living environment. This is referred to as the relative humidity which, for practical purposes, is considered to be the amount of water vapor in the air compared to the amount the air can hold at a given temperature. Keeping relative humidity below 50% is critical to create an environment that doesn't sustain mold, mildew, or dust mites.

Humidity Control Products

Humidifiers and dehumidifiers are often used to control moisture in a home. The following section focuses on products that add moisture.

A properly sized and installed whole-house humidifier can correct many of the problems associated with air that's too dry. It's important to choose the type of humidifier that best suits the application. Here are some options:

A flow-through bypass humidifier usually has no fan. It bypasses a portion of the forced air from the supply side of the furnace, forcing it across a water panel or media. The humidified air is then routed to the return side of the furnace, blending with air from the cold air returns. The pre-humidified air is then heated by the furnace and delivered to the conditioned space.

A flow-through or power humidifier, has a built-in fan which pulls heated air directly from the hot air (supply) side of the furnace, pushes it across a water panel or media where warm air picks up humidity, and flows back to the supply duct. The humidified air blends with air exiting the furnace and is distributed throughout the home.

Drum humidifiers are best suited for homes without a drain located near the heating/cooling equipment, or for homes in areas where water costs are relatively high. Drum units rotate a pad through a reservoir of water, and warm air blows over the pad to evaporate the water. Some units come equipped with an optional flushing timer that may be used to periodically clean minerals from the reservoir.

Steam humidifiers are capable of independently operating the furnace blower motor to distribute humidified air when needed. This provides humidification in addition to those times when the blower operates within normal cycles.

All humidifiers must be serviced at some point in time. For instance, steam units build up scale on the heating element and in the reservoir. If hard water or high mineral content is observed in the water, the humidifier will require service more often.

Successful IAQ Strategy

Delivering on the promise of providing comfort to your customer requires that you understand all the tools that can impact IAQ. Contractors who are prepared to answer all of their customers’ questions will be prepared for success.


How HVAC Affects IAQ

Note that one or more of these conditions may exist. A single symptom may be the result of several problems, and a single problem may produce multiple symptoms.

While the most common complaints regarding indoor environments are hot and cold calls from homeowners. The most common measured value is an elevated wet bulb temperature, or high humidity. Any or all of the following can produce these symptoms:

  1. Thermostat location relative to the occupied load
  2. Actual occupancy and use versus the intended use
  3. Changes to the building envelope during construction that may adversely affect the HVAC performance
  4. Difficult access to system components for testing, balancing, and service. Access to service equipment, particularly filters, that is difficult or impossible will mean it will lack appropriate service and air quality will be compromised
  5. Duct leakage that prevents sufficient flow to the occupied space. (Example: improperly sealed ductwork can lose 20 to 40% of the airflow)
  6. Occupants making adjustments to previously balanced conditions (Example: closing off one or more rooms to conserve energy)
  7. Uninformed HVAC personnel making adjustments to previously balanced conditions who are under pressure to "just fix it" without assessing all of the possible problems that can produce the symptoms of "too hot/too cold"
  8. Adding devices to a system that lacks the capacity to handle the additional load. (Example: high efficiency pleated filters may present too much restriction of air flow)
  9. Over-sized systems that don't operate long enough to provide adequate dehumidification.