About HVAC
Heating, Ventilation, Air Conditioning

How should a residential HVAC system be cleaned?
The most effective way to clean air ducts and ventilation systems is to employ Source Removal methods of cleaning. This requires a contractor to place the system under negative pressure, through the use of a specialized, powerful vacuum. While the vacuum draws air through the system, devices are inserted into the ducts to dislodge any debris that might be stuck to interior surfaces. The debris can then travel down the ducts to the vacuum, which removes it from the system and the home.

What kind of equipment is best for cleaning-truck mounted vacuums or portable vacuums? 
NADCA does not endorse one kind of equipment over another. There are two main types of vacuum collection devices: (1) those mounted on trucks and trailers, and (2) portable units. Truck/trailer mounted equipment is generally more powerful than portable equipment. However, portable equipment can often be brought directly into a facility, allowing the vacuum source to be located closer to the ductwork. Both types of equipment will clean to NADCA standards. 

All vacuum units should be attached to a collection device for safe containment prior to disposal. Any vacuum collection device which exhausts indoors must be HEPA (high efficiency particulate arrestance) filtered.

A vacuum collection device alone will not get an HVAC system clean. The use of methods and tools designed to agitate debris adhered to the surfaces within the system, in conjunction with the use of the vacuum collection devices), is required to clean HVAC systems. (For example: brushes, air whips, and "skipper balls.")

How often should residential HVAC systems be cleaned?
Frequency of cleaning depends on several factors, not the least of which is the preference of the homeowner. Some of the things that may lead a home owner to consider more frequent cleaning include:

  • Smokers in the household.
  • Pets that shed high amounts of hair and dander. 
  • Water contamination or damage to the home or HVAC system. 
  • Residents with allergies or asthma who might benefit from a reduction in the amount of indoor air pollutants in the home's HVAC system. 
  • After home renovations or remodeling. 
  • Prior to occupancy of a new home. 

What is the normal price range for the air duct cleaning service? 
The Environmental Protection Agency says that "duct cleaning services typically - but not always - range in cost from $650 to $1000 per heating and cooling system, depending on the services offered, the size of the system to be cleaned, system accessibility, climactic region, and level of contamination" and type of duct material. Consumers should beware of air duct cleaning companies making sweeping claims about the health benefits of duct cleaning - such claims are unsubstantiated. 

Consumers should also beware of "blow-and-go" air duct cleaning companies. These companies often charge a nominal fee and do a poor job of cleaning the heating and cooling system. Representatives often show up in their own cars as opposed to company vehicles with nothing more than a vacuum unit similar to a shopvac. These companies may also persuade the consumer into un-needed services with or without their permission. (If you have knowledge of a practicing "blow-and-go" air duct cleaner, contact your local Better Business Bureau to report the company, and your local, federal, and state elected officials to demand legislation.)

Amount of Ventilation
If too little outdoor air enters a home, pollutants can accumulate to levels that can pose health and comfort problems. Unless they are built with special mechanical means of ventilation, homes that are designed and constructed to minimize the amount of outdoor air that can "leak" into and out of the home may have higher pollutant levels than other homes. However, because some weather conditions can drastically reduce the amount of outdoor air that enters a home, pollutants can build up even in homes that are normally considered "leaky".

How Does Outdoor Air Enter a House?
Outdoor air enters and leaves a house by: infiltration, natural ventilation, and mechanical ventilation. In a process known as infiltration, outdoor air flows into the house through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors. In natural ventilation, air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between indoors and outdoors and by wind. Finally, there are a number of mechanical ventilation devices, from outdoor-vented fans that intermittently remove air from a single room, such as bathrooms and kitchen, to air handling systems that use fans and duct work to continuously remove indoor air and distribute filtered and conditioned outdoor air to strategic points throughout the house. The rate at which outdoor air replaces indoor air is described as the air exchange rate. When there is little infiltration, natural ventilation, or mechanical ventilation, the air exchange rate is low and pollutant levels can increase.

Flood Restoration and Decontamination
The most significant event that precipitates building wide water damage and subsequent environmental hazards associated with extensive microbiological contamination is some type of flooding episode, whether it be from heavy rains, a broken water line or other catastrophic event. Fortunately, proper techniques following a water damage event can eliminate or significantly reduce microbial damage. Rapid response is critical. A restoration or remediation company should be on site within 8 hours of a flooding episode. The restoration company must also have the proper equipment to perform the task quickly and efficiently, including water extraction and dehumidification equipment.

At a minimum the restoration company should:

  • Remove carpet and pad.
  • Remove cove moldings or other moldings if water has entered wall cavity.
  • Drill holes in wallboard to facilitate drying inside wall cavity.
  • Pay special attention to built in cabinets, remove kick plates or drill holes.
  • Have special equipment for remediation of microbiological contamination if necessary.
  • If the damage is by anything other than clean water (potable water) special precautions must be taken. In sewage situations, pathogenic bacteria and viruses must be dealt with by evacuation of occupants until cleanup and disinfection has been completed. Workers entering the contaminated area must wear protective clothing and respirators.

  • Microbiological contamination is a concern if cleanup and drying is not accomplished expediently. Clean water floods that are not dried out rapidly will require extensive demolition and removal of porous materials. A microbiologically damaged structure is not a safe environment. If significant mold growth occurs, the occupants of the structure should be evacuated. 

Every situation is unique but as a general rule of thumb remediation personnel should:

  • Equip remediation workers with protective equipment.
  • Contain the area in need of remediation.
  • Exercise extreme care when removing contaminated materials and bag them before removing them from the contaminated area.
  • Remove contaminated or water damaged porous organic materials and discard.
  • Drywall, ceiling material, insulation.
  • Flooring, carpet, pad, sub floor material, cabinets with particle board bases.
  • Remove spores and other fungal particulates from the air and from surfaces. - HEPA filters - HEPA vacuums

Use negative air containment to protect other parts of the structure during demolition.
Use HEPA filters to clear the air after demolition.
Treatment of contaminated porous materials with biocides is not effective. Biocides inhibit growth but most are not sporicidal. Nonviable fungi remain allergenic and toxigenic.

Ten Things You Should Know About Mold

  1. Potential health effects and symptoms associated with mold exposures include allergic reactions, asthma, and other respiratory complaints
  2. There is no practical way to eliminate all mold and mold spores in the indoor environment; the way to control indoor mold growth is to control moisture.
  3. If mold is a problem in your home or school, you must clean up the mold and eliminate sources of moisture.
  4. Fix the source of the water problem or leak to prevent mold growth.
  5. Reduce indoor humidity (to 30-60% ) to decrease mold growth by: venting bathrooms, dryers, and other moisture-generating sources to the outside; using air conditioners and de-humidifiers; increasing ventilation; and using exhaust fans whenever cooking, dishwashing, and cleaning.
  6. Clean and dry any damp or wet building materials and furnishings within 24-48 hours to prevent mold growth.
  7. Clean mold off hard surfaces with water and detergent, and dry completely. Absorbent materials such as ceiling tiles, that are moldy, may need to be replaced.

  8. Prevent condensation: Reduce the potential for condensation on cold surfaces (i.e., windows, piping, exterior walls, roof, or floors) by adding insulation.
  9. In areas where there is a perpetual moisture problem, do not install carpeting (i.e., by drinking fountains, by classroom sinks, or on concrete floors with leaks or frequent condensation).

  10. Molds can be found almost anywhere; they can grow on virtually any substance, providing moisture is present. There are molds that can grow on wood, paper, carpet, and foods.

Sick Building Syndrome (SBS)
A building is defined as sick if 20 percent or more of the building's occupants complain of such problems as headache, eye irritation, nausea, sore throats, dry or itchy skin, sinus congestion, nose irritation, fatigue and dizziness for more than two weeks; If the symptoms are relieved when the complainant leaves the building; and, if no specific cause of the problem can be identified. (ASHRAE Journal, July 1988, p.40) 

Mold/Asthma Related Resources

Mold growth may be a problem after flooding. EPA's Fact Sheet: Flood Cleanup: Avoiding Indoor Air Quality Problems - discusses steps to take when cleaning and repairing a home after flooding. Excess moisture in the home is cause for concern about indoor air quality primarily because it provides breeding conditions for microorganisms. This fact sheet provides tips to avoid creating indoor air quality problems during cleanup. U.S. EPA, EPA Document Number 402-F-93-005, August 1993.

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