This article was written by the owner of 4 Corners Home Inspections & Environmental, Barry Mankin. ACI, and published in the July 2024 issue of the ASHI Reporter, the membership magazine produced by the American Society of Home Inspectors.
With all of the recent buzz around indoor air quality issues, let’s talk about what we refer to as the lungs of the home—the HVAC system. HVAC can be a wild card in the indoor air quality industry, especially as it relates to the residential side. Unlike commercial buildings that have high-end ventilation systems for high traffic, pressurization, and a myriad of different influences that have to be managed, residential air quality issues are often overlooked, despite often having simple solutions. The pain points we typically find are usually when someone is sick or scared of mold in their own home.
As home inspectors, we have a limited scope of what we actually see. Typically, we refer to the experts to take on that liability beyond our visual inspection. Our approach to our business model is a bit different than most, and I would like to offer some suggestions to help people reach better air quality related to HVAC.
Tips for Inspecting HVAC
During home inspections, our inspectors are trained to visually assess the HVAC system, including inspecting the filters, the inside of the return, and inside a representative number of supply vents. This is a simple thing to do that does not take much time. If someone’s ducts are dirty, we mention it as a maintenance item for improvement. It’s such a simple thing but can pay huge dividends for the health of future inhabitants.
Let’s talk filters. Other than filters not being changed regularly, they are usually too restrictive. Allow me to explain: Here in the South, the main job of air conditioning in summer is to pull moisture out of the air because, due to our high relative humidity, we’re mostly managing moisture. As it relates to indoor air quality and mold—the “M word” nobody wants to mention—mold needs food and water to grow, just like humans.
Restricting air flow by design can elevate indoor relative humidity and allow vulnerable areas to achieve dewpoint. Condensation can be tricky, and dewpoint of surfaces also comes into play around registers with a lack of insulation from non-controlled spaces and areas not being sealed as well. Leaky or compromised ductwork, filters that are too restrictive—like an allergen or HEPA style filter system—undersized ducts, layout issues, combustion air makeup, improperly sized tonnage, or debris can all cause issues.
If properly designed, the two simplest things that can cause condensation is debris and filter restriction. This can lead to inefficiency and condensation, which leads to moisture leaks on all types of surfaces, again leading to the dreaded “M word.” We recommend ductwork cleaning and sanitization on most homes we see because most homeowners are not proactive, and builders do not clean “food sources” like drywall dust and construction debris before they sell a new home. Most systems have been running, drawing debris in, and the coils become grounds for mold, again with the food and water located right where the airflow blows against it to spread it throughout the home.
4 Steps for Cleaning Ductwork
Now let’s talk about the cleaning process. There are four stages of ductwork cleaning that all ductwork cleaning companies should do. Missing one of these four components loses the integrity of the process, and in many cases can create more significant health issues.
1. Whether flex or metal ductwork, there may be debris on walls throughout. The coils and interior of the unit should be thoroughly examined for cleaning, and any interior insulation that is compromised with mold should be removed. Most manufacturers are now suggesting wrapping the outsides of the plenum with insulation, as opposed to the interior, for this very reason. The insulation absorbs condensation and debris, which grows mold.
2. Validating the integrity of the system and the cleaning process with a camera should always be performed. Many companies do not clean the main lines or returns all the way through. This must be done along with the validation. If the main lines are not cleaned, the rest of the system gets contaminated after the process is complete.
3. If the coils aren’t cleaned, the rest of the system is contaminated in the same manner.
4. Sanitize with an antimicrobial. This can be implemented by a fogging process or a light spray. We always recommend green products for this application. This process is not always an apples to apples comparison when looking for reputable companies to recommend to your customers. They must perform all four of these steps to be comprehensive—and to truly be clean.
Here in Tennessee, not only do we have pollen, mold, bugs, and so forth, but we also have high relative humidity, as stated before. Now we are pumping food and water directly into a sealed HVAC system, which, again, impacts indoor air quality. Fresh air makeup is only fresh if it’s controlled from the outside.
Other Considerations
You may also see glowing lights coming out of a UV probe. These probes should be installed underneath the coil; it is advantageous to help keep the coil clean. Note that it does not put magic pixie dust in the air and clean the indoor air or all the debris that is still in the system. Many people may claim this, but it is simply not true. There are several other types of systems that are more involved and go through different areas throughout the ductwork. In many situations, this technology can be in locations where the light can break down filters, flex, or insulation and create particulate issues that are transferred into the interior of the home. As always, refer to an air quality expert if there are any questions in diagnosing these types of applications. HEPA filter systems, electronic filtering systems, etc. would also fall under this category for referral.
In other parts of the country, we have in-line humidifiers. Generally, again going back to mold needing food and water, if the ducts are dirty and there is an old humidification system that is not strictly maintained, there will be mold inside the ductwork, potentially blowing around the house.
Here, we always recommend for those to be removed and the ductwork to be cleaned and sanitized. If this house is large enough to warrant this type of application, we recommend a steam system that is strictly maintained on an annual basis. Most people don’t even know what they are, and they all leak or have leaked in the past. They are very beneficial, but again, would require annual maintenance for the integrity of that system as long as the system is clean.
Lastly, due to the tightness of today’s homes for energy efficiency standards, combustion, or fresh air makeup, is the other wild card. Builders are not required to have complex ventilation systems like in commercial buildings; however, I believe positive pressure systems will be needed in the future for all residential homes. There are simple ways to do this with filtering and a dehumidifier application while mixing the air. With that said, code-compliant combustion air makeup is usually unfiltered air from the outside tied directly into the HVAC system.
Some will have controls from vent hoods to activate that, but that only checks the box for oxygen. It does not help the air quality at all. Here in Tennessee, not only do we have pollen, mold, bugs, and so forth, but we also have high relative humidity, as stated before. Now we are pumping food and water directly into a sealed HVAC system, which, again, impacts indoor air quality. Fresh air makeup is only fresh if it’s controlled from the outside. Remember, many HVAC companies only address what they know for efficiency and are limited in their scope as it relates to air quality. Or they may have financial motivation to sell products to make a quick buck. This is another situation where it is best to recommend an air quality expert. Our goal in our other businesses is to help people find balance between their energy efficiency and indoor air quality so they can have healthy homes. If the lungs are compromised in the home, then the inhabitant’s lungs will be compromised as well. Unfortunately, this issue will only get worse in the residential market if we are not intentional with working to achieve that balance.