January, 2007
Inspection News and Views from the American Society of Home Inspectors

An HVAC Story: Is There Anything Right With This System?


HVAC system hygiene is one of the most frequently ignored or misunderstood components of indoor environmental quality. The heating, ventilation and air-conditioning system can serve as a transport system for contaminants and, in some instances, can actually be the source of those contaminants. Yet in many indoor environmental assessments of both commercial and residential buildings, the HVAC system is treated as an afterthought.

In my business, I read literally hundreds of building assessment reports in the course of a given year and, often, the only reference to HVAC system hygiene is a line or two about cleaning the ductwork. The intricacies of HVAC system hygiene can rarely be addressed by simply cleaning the ductwork.

In the following case study, I will describe a real-life scenario that happened recently and truly highlights how complex and diverse the potential indoor environmental concerns associated with HVAC systems can be. After reading this case study, I think the reader will ask: Is there anything right with this system?

The Scenario

The woman’s voice on the other end of the phone sounded extremely distraught. She had been referred to me by her mother, for whom I had done some work the previous year. The frantic woman explained that every time she turned on the heat, she was having a terrible reaction. Since she had recently been diagnosed with mold allergies, she was afraid that there could be mold in her HVAC system.

She said she was having her house “tested” for mold but wanted to take her mother’s recommendation to have me look at her HVAC system and give her a cost for cleaning. I suggested that she wait until the results of the testing came back so that we could look at the bigger picture, but she pleaded with me to come out immediately. Finally, I agreed to come out that afternoon.

The house was a luxury townhouse in a luxury townhouse complex in a very luxurious area. (My reason for stressing the luxury aspect will be made clear later on.) She greeted me at the door accompanied by a young man whom she introduced as the consultant who was performing the mold testing. She pointed me toward the finished basement where the HVAC unit was located and said she would leave me alone to look at what I needed to look at. To my surprise, the consultant asked if he could accompany me and ask some questions, and I said, “Sure.”

As we walked downstairs, I asked him what type of assessment he was doing, and he informed me that he was taking air samples throughout the house to see if there were any elevated mold levels in the air. I asked him if there was any evidence of water damage or odor problems or visible mold growth anywhere, and he said no. I asked him if he had looked at the HVAC system, and he said no. I wondered what he would recommend if his test results came back as elevated, but I bit my tongue.

The HVAC unit was in a small mechanical room. I switched off the power, locked it out and popped the front
panels off the unit. I shined my light into the blower compartment, looked around, stepped back and looked at the system and room as a whole. I turned to the consultant and asked him what he thought, and he threw it back at me and asked what I thought. We were at an impasse! Reflecting on the idea that it is usually easier to look smart if one keeps one’s mouth shut, I then threw caution to the wind and proceeded to point out those items that I saw as at the least potential concerns.

I pointed out that although the filter was a decent quality pleated filter, the side of the filter compartment was completely open. I also pointed out that the mechanical room was extremely dirty and that less than 12 inches away was a sump pump well with standing water.

Shining my light into the blower compartment, I could see that the return air coming into the right side of the blower compartment was filtered, but there was another return on the back left side that was not filtered at all. The blower motor fan blades were clogged with caked-on debris.

Photo: Dust and debris buildup can be seen on this ripped and torn piece of flexible duct insulation.

Moving up the exterior of the air-handling unit to the supply plenum, I next pointed out the humidifier that had been sloppily installed. Rust and corrosion were running down the front of the sheet metal under the humidifier, and a knock on the plenum confirmed that it was internally lined with fiberglass. I also determined that the coil was inside that lined box and that there was not any access door to gain entry to the coil.

Moving outward along the supply ductwork, there were a couple of short flexible duct sections that dumped into small lined boxes that each had two or three flexible duct lines that extended outward through the solid basement ceiling or upward into the main house. I managed to pop my head above the open section of ceiling in the mechanical room and observed a snaking mass of flexible ducting wriggling in all directions. I paced off a few of the longer duct runs, and they easily ran 50 feet or more.

Right about this time, my young consultant friend was looking a bit glassy-eyed. I asked him if he had inspected the coil or lining, and he responded that there was not an access door. I suggested that one of the short flexible duct sections could be removed to gain access, and he replied that he was not a “mechanical” guy and was not allowed to take things apart. I felt no such inhibition and
gingerly clipped the zip tie and slowly eased the flexible ducting off of the cuff just enough to peak inside.

Photo: Mold is seen growing in the insulation.

Photo: The internal lining of this HVAC ductwork is torn.


Photo: The internal lining of this cooling coil shows much abrasion.

Trying to avoid overly disturbing what could be inside, I eased in to get a look. The coil was completely black with debris and degraded lining. The edges of the lining had been cut to facilitate the installation of the humidifier, and they were badly frayed. All of the lining that I could see had significant water staining, was badly abraded, discolored, dirty and appeared to have visible microbial growth. I carefully reattached the flexible ducting and put on a new tie.

I put the unit back together, removed my lock and turned the power back on. I did not turn the system on. I met briefly with the homeowner and described what I had found. I informed her that given the number of things that were wrong with her system, I was unwilling to simply “clean” it. I told her that although I could put together a remediation plan, she might want to consider replacement. I explained to her that there were  fundamental design flaws that would be costly to correct and that since the system was more than 12 years old, replacement might deliver a better value in the long term.

She thanked me for the advice and said she would talk it over with her husband. As I walked up the stairs to leave, I noticed that the consultant had gone back to finishing his air sampling.

Two days later, the woman called to tell me that she was looking into having her HVAC system replaced and that she had hired a different consultant to evaluate her home further.

Conclusions, and Some Thoughts

I told this story exactly as it happened. I did not tell it to denigrate consultants or to show how smart I am, because I certainly know that I am not all that smart. I do not know if the described HVAC system is affecting that woman’s health in any way, and I would never make that claim. However, let’s look at what I did find and how it might possibly be impacting the indoor environment:

• The side of the filter compartment was open, and the mechanical room was very dirty with an open sump pump well with standing water. There were also paints and chemicals stored in the mechanical room. When the blower is in operation, the blower chamber is pulling a negative pressure, and the gaps around the open filter compartment could pull potential contaminants into the system distributing them into the living space.

• There was an unfiltered return at the back of the blower compartment, and the blower motor fan blades were clogged with caked-on debris. Certainly, this shows a potential for particulates that get pulled in through the return to be redistributed back into the living space. The buildup on the fan blades shows that in fact particulates are accumulating in the system serving not only to reduce efficiency but also as a growth medium for microbial growth.

• The leaking humidifier was clearly saturating the deteriorating and dirty fiberglass lining. I would suggest that this is much like having a very dirty sponge in the air stream, and there is certainly the potential for elevated microbial growth. There is also the potential for fiberglass fibers and accumulated debris to migrate out into the living space.

• The impacted coil could be dramatically reducing system efficiency and is also a prime suspect for elevated microbial growth.

• The internally lined diverter boxes are suspect because of their close proximity to both the humidifier and the coil. If the conditions already found within this system are any indicators, it is likely that the interior of those boxes are dirty, water-stained and deteriorating. Further investigation would be necessary to determine the validity of this theory, but if it is accurate, there is another source for microbial growth, debris and fiberglass particles.

• The snaking labyrinth of flexible ducting detracts from system efficiency, and the dipping troughs inside the ducting are great places for debris to accumulate.

I would like to say that the system that I described is highly unusual. Certainly, most HVAC systems do not have as many things wrong with them as this system did.

But in reality, many of the described conditions are all too common. The HVAC system in this story was in a luxury townhouse, and yet its design and maintenance were hideous. A mechanical contractor regularly serviced the system, and yet it was dirty and deteriorating. A consultant was brought in to assess potential health concerns in the home, and yet the HVAC system was not even considered—despite the fact that the woman clearly stated that she had symptoms only when the heat was turned on.

So, why was it that she had symptoms only when the heat was turned on but not when she operated the air conditioning? I have an opinion, but I would love to hear what others think.

This article is reprinted from Volume 7, Issue 1 (November 2005) of Indoor Environment Connections newspaper. For subscription information, visit www.ieconnections.com.