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
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
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
- 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
- Drill holes in wallboard to facilitate drying inside wall cavity.
- Pay special attention to built in cabinets, remove kick plates or
- 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
Every situation is unique but as a general rule of thumb remediation
- 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
- Drywall, ceiling material, insulation.
- Flooring, carpet, pad, sub floor material, cabinets with particle
- 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
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
- Potential health effects and symptoms associated with mold exposures
include allergic reactions, asthma, and other respiratory complaints
- 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
- If mold is a problem in your home or school, you must clean up the
mold and eliminate sources of moisture.
- Fix the source of the water problem or leak to prevent mold growth.
- 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
- Clean and dry any damp or wet building materials and furnishings
within 24-48 hours to prevent mold growth.
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.
- Prevent condensation: Reduce the potential for condensation on cold
surfaces (i.e., windows, piping, exterior walls, roof, or floors) by
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).
- 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.