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Cashins & Associates Blog

Indoor Air Quality - HVAC Inspections

Posted by Mike Cashins on Thu, May, 31, 2012 @ 11:05 AM


Various environmental pollutants will inevitably build up in an occupied indoor environment over time.  Items including office equipment, cleaning solutions, carpets, and building materials can produce gases, odors, and dust.  In a building that has a properly functioning ventilation system, these pollutants will be diluted and removed from the occupied space.  Building ventilation is critical in removing airborne contaminants and providing a constant supply of fresh air.  Many indoor air quality problems are the result of inadequate or malfunctioning ventilation systems. 

This 10-part checklist is meant to be used as a tool for facilities and property management personnel in helping identify the potential causes of indoor air quality problems.  In addition, it may serve to help develop a system whereby IAQ issues may be avoided.  It includes a list of various HVAC components and aspects of design that can have direct impact on the indoor environment.  It also includes recommendations for regular inspection and maintenance.

1.      Check the thermostats.  Are they set to “auto” or “on”?

Thermostats should always be in the “on” position.  In “auto” mode, the system will only supply fresh outdoor air when the thermostat demands it, depending on the temperature within the building.  If the temperature does not need to be adjusted, no air is supplied.  This is one of the most common mistakes related to IAQ found in office settings.

2.      HVAC filters

How often are the filters replaced in your building?  Do you have a written protocol for routine inspections and replacement?  Are you using the appropriate type of filter for your system?

Check the Minimum Efficiency Reporting Value (MERV) of the filters to make sure they are sufficient for the desired purpose.  A normal office unit will require a filter with a MERV value of at least 8, which are sufficient for the removal of such contaminants as mold spores, dust mite body parts and droppings, and cat and dog dander

3.      Outdoor air dampers and actuators

Many times, the amount of fresh outdoor air that is supposed to be provided to a space differs greatly from what is actually brought in.  This is sometimes due to problems with air dampers and actuators.  These should be checked at least every three months or in accordance with the Operations & Maintenance manual.

4.      Humidifiers

Humidifiers, by definition, provide moisture to the HVAC system.  If it is not running properly, or is damaged, moisture may enter other sections of the system, causing microbial growth and structural damage.  Humidifiers should be inspected for mechanical and structural integrity, as well as for cleanliness, at least every three months or in accordance with the Operations & Maintenance manual.

5.      Cooling coils

Cooling coils, if left alone and not inspected routinely, are likely to become dirty, and create a buildup of moisture.  This moisture, when it comes in contact with the organic material on the coils, can lead to microbial growth.  It is very important that these are inspected and, if necessary, cleaned regularly. Inspections should be performed no less than once per year.

6.      Drain pans and adjacent surfaces

A major culprit in the introduction of unwanted microbial entrainment is the unmaintained drain pan.  The purpose of the drain pan is to collect condensate from the coils, and to expel the water through an opening at the bottom of the sloped pan.  It is important that the slope be sufficient so as to divert water into the drain.  Further, it is essential that the drain not become clogged by rust, organic matter, or foreign objects.  This can lead to a buildup within the pan, and can create an environment ideal for microbial growth.

Drain pans and surrounding areas should be inspected at least once per year during the cooling season.

7.      Outdoor air intake louvers, bird screens, mist eliminators, and adjacent areas

These items help prevent larger foreign bodies from entering the HVAC unit.  It is imperative that they are structurally sound and fully operational.  Broken or poorly functioning barriers can allow these objects entry, which can then in turn cause mechanical and microbial problems.

Intake louvers, bird screens, and mist eliminators should be inspected every six months or as specified in the Operations & Maintenance manual.

8.      Cooling towers

Cooling towers allow heat collected from cooling systems to be released to the outdoors.  These systems can cause major air quality problems if left unattended.  Bacteria, such as Legionella, thrive in stagnant water, and can cause serious illness for those exposed.  For this reason, an Operations & Maintenance manual must state how frequently the inspections should be carried out.  This information can be obtained by the treatment system provider.

9.      Floor drains in plenums or in rooms used as plenums

Floor drains are notorious for backing up and causing problems.  When this happens, water can stagnate and allow for the growth of microbial organisms.   If the drain is located within a plenum or a room that is used as a plenum, these microorganisms may be entrained into the HVAC duct system.

It is important to inspect and, if necessary, clean or repair these drains.  This should be done periodically in accordance with the Operations & Maintenance manual.

10.  Outdoor Air Intake Location

Ensure that outdoor air intakes are located the prescribed distance from various potential pollutant sources, such as exhaust vents, garage entrances, garbage storage areas, truck loading locations, and the like.  The following table summarizes recommended separation distances between air intakes and various potential outdoor contaminants.


Minimum Distance, ft

Cooling tower exhaust


Garbage storage/pick up area, dumpsters


Thoroughfare with high traffic volume


Truck loading area, bus idling area


Garage entry, automobile loading area


Vents, chimneys, and flues from combustion appliances and equipment


Plumbing vents terminating less than 3 feet above the level of the intake


Plumbing vents terminating at least 3 feet above the level of the intake


This checklist is not by any means comprehensive, and is not meant to be used as a substitute for a full assessment by an industrial hygiene professional.  It is meant to be used as a tool for determining whether or not an indoor air quality problem may exist, and also to provide assistance in preventing air quality issues from occurring.  It is always recommended that a professional industrial hygiene consultant be retained in situations where indoor air quality may be compromised. 

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Topics: indoor air quality, ventilation assessment

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