In HVAC, we have a few infamous indoor air quality monsters that bring terror to our customers’ homes—gases, particles, and organisms that wreak havoc on indoor air quality (and may contribute to moderate to severe health problems). The big one is carbon monoxide (CO), which we all know is deadly. Although not deadly by itself, those of you in humid climates might think of water vapor. Allergy-aggravating pollen, fungal spores, and pet dander also make the list. Now, how many of you thought about VOCs?

VOCs, or volatile organic compounds, can be found in just about every building and are often associated with distinctly chemical odors. They’re practically impossible to escape; they’re in cleaners, glues, the very materials used to build and furnish houses, and even clothes and bedding. The problem is that they’re also linked to short-term discomfort and long-term organ damage.

Unfortunately, many people aren’t aware of how harmful and pervasive VOCs are. The responsibility of informing people about the risks of VOCs is on us, the HVAC contractors. We have to rely on a mix of customer education, ventilation, humidity control, and source control to keep VOCs at bay.

What are VOCs?

VOCs are organic compounds, meaning they contain carbon. Solid and liquid VOCs evaporate easily at room temperature. As such, they’re commonly given off by many household objects. Some of these objects aren’t too surprising, like the following items we often associate with fumes and potentially harmful chemicals:

• Cleaners (including bleach)
• Paints
• Varnishes
• Adhesives

There are far more, though, including furniture, upholstery, and plastics. New car smell is an example of what happens when VOCs off-gas. It’s a distinctly chemical odor, and while some people like it, it makes some people feel nauseous or get headaches. 

Another prominent source of VOCs is air fresheners, scent diffusers, candles, and scented wax warmers. How many of you have walked into a house to the smell of “fresh” lemon, lavender, balsams, or cotton? I’d be surprised if there’s a residential HVAC tech out there who hasn’t. Customers love using candles and air fresheners to hide odors, but it comes at a cost.

VOC Types and Health Effects 

The CDC’s Agency for Toxic Substances and Disease Registry (ATSDR) has a full list of VOCs, but we’ll cover some of the most common ones. You may recognize some of these names.

If you remember dissections back in school, you’re probably familiar with formaldehyde. This substance, the same one used to preserve specimens, is a VOC, and it’s also used in building materials (like plywood and insulation), adhesives, resins, and even textiles. It’s also a carcinogen.

Benzene has some similar uses to formaldehyde in manufacturing, including the production of plastics and resins. This one has a sweet sort of smell that you might recognize each time you fuel up your truck… gasoline. This one is also a carcinogen, and paraffin wax candles specifically give it off when burned.

Here are some other VOCs you might recognize by name (and smell or usage):

• Acetone (nail polish remover)
• Chloroform (formerly an anesthetic)
• Vinyl chloride (PVC pipe)

There are many, many more, which you can view by clicking the link above. This short list just gives an overview of how dangerous and ever-present VOCs can be in our customers’ homes.

Short-Term Health Effects

Are you one of those people who get headaches and feel nauseous when you sit in a brand-new car for a while? Or what about in a room that has been painted recently? You’ve experienced the short-term effects of VOC exposure.

A list of common effects of short-term VOC exposure is as follows:

• Headaches
• Dizziness
• Nausea
• Irritation of the eyes, nose, and throat
• Allergic reactions on the skin
• Fatigue

Long-Term Health Effects

We’ve already said that some VOCs are carcinogenic, meaning they’ve been linked to cancer. This phenomenon has been observed in studies on animals, and formaldehyde and benzene specifically are considered to be human carcinogens. (The Lawrence Berkeley National Library has some more information about research on the link between VOCs and cancer HERE.)

Major organ damage is another problem. Here are some organs and organ systems that are most likely to experience complications associated with chronic VOC exposure:

• Kidneys (urinary and endocrine systems)
• Liver (digestive system)
• Central nervous system (includes brain, spinal cord, and nerves)

How VOCs Interact with Other Factors in a Home

VOCs undergo chemical reactions at room temperature, but the rate at which they off-gas and their concentration in a building are all affected by aspects of a building that we can control, at least to some extent.

When VOCs off-gas, they desorb from the substance or material; desorption is a chemical reaction that is the inverse of adsorption. Adsorption is when substances cling to a surface instead of being absorbed into it, and desorption is when the bond between the clinging substance (adsorbate) and the surface (adsorbent) is weakened, causing the adsorbate to release back into the air. Like many other chemical reactions, higher temperatures and humidity levels can exacerbate the desorption process.

Similarly, VOCs will be released at a higher rate with elevated temperatures and humidity levels. That’s bad news when your customer is in a humid living room with a new couch. The VOCs in the fabric will off-gas at a more rapid rate, which may cause a chemical odor and respiratory irritation. Humidity is also a problem when people store cleaners in cabinets under sinks, which is a very common practice in homes. Many chemicals come in spray bottles or have screw-on caps, which aren’t very secure, meaning those chemicals are off-gassing right underneath the kitchen or bathroom sink. 

Ventilation also matters. A tight home with little ventilation will keep the VOCs from escaping. A home with good, controlled ventilation can dilute the concentration of VOCs in the air, making them less likely to cause adverse health effects. It’s the same principle as using ventilation to dilute respiratory viruses; cells in a healthy immune system can attack a few viruses easily, but you get sick when exposed to higher concentrations because your body has a harder time fighting them.

How to Fight Off VOCs

As with other IAQ concerns like viruses and solid airborne particles (like smoke, dust, etc.), we need to start by collecting data and educating the customer. Then, we can focus on the main things that will create solutions. In the case of VOCs, the main mitigation methods are source control and ventilation.

Measuring VOCs

While you could probably tell if there’s a VOC problem by smell or by noticing things like plug-in air fresheners and cleaning chemicals, we need to be able to quantify the VOCs before we prescribe a solution. There are several IAQ monitors, including HAVEN IAQ’s Central Air Monitor, that can collect TVOC data. 

TVOC stands for “total VOCs,” meaning it captures the total concentration of VOCs in a sample, not individual counts for formaldehyde or benzene. However, there are a few monitors on the market now that measure formaldehyde concentrations and other VOCs as two separate categories, which can be useful.

Average TVOC levels should not exceed 500 micrograms (one millionth of a gram) per cubic meter of air. Levels below 300 micrograms per cubic meter are ideal, and levels between 300 and 500 micrograms are okay, but TVOC levels that consistently exceed the 500-microgram threshold indicate a need to reduce the VOC concentrations.

Once we know the VOC levels we’re dealing with in a given home, we can start educating the customer about solutions. 

Source Control

One of the easiest and most inexpensive ways for a customer to handle high VOC concentrations in their homes is to focus on source control.

This step is as simple as informing customers that it’s safer to store cleaners, paints, and other chemicals away from the home, such as in a shed or detached garage. Sometimes, that’s not possible, so another method is to keep the chemicals in a sealed container if they must be stored indoors. The same goes for educating customers about the real effects of plug-in air fresheners, candles, and essential oil diffusers; while those may smell good or mask odors, they’re not good for our health.  

Source control gets a little trickier once furniture, bedding, flooring, and clothing are involved, as you can’t exactly keep those outside the home. The best thing you can do is have those surfaces appropriately cleaned. Clothes should go to the dry cleaner, and fabric furniture and carpeting could be steam-cleaned to help reduce VOC off-gassing.

Humidity Control

Most air monitors that measure VOCs can also measure humidity. Some smart thermostats do that as well. These readings can also provide us with some clues about whether the indoor humidity is feeding the VOC problem.

Remember when we said that higher humidity levels lead to increased VOC off-gassing? This pretty well-known chart shows exactly what we mean (VOCs are represented by chemical interactions):

VOCs can and will off-gas in the healthy zone, but off-gassing gets worse once we reach 60% relative humidity and above. The typical healthy range is 30–60% RH, so humidity control can keep VOCs at bay to some extent. 

Of course, we get some degree of dehumidification from the HVAC system when water vapor condenses on the evaporator coil. Oversized systems are less effective at dehumidifying due to shorter runtimes, so proper sizing according to ACCA Manual S can help. 

Eliminating bulk water is another big step, and it may not be our responsibility to fix most bulk water sources, but we can at least identify them. Bulk water happens when water is allowed to pool in an area inside or near a structure. This water may enter directly via something like a leak, or it can happen when standing water outdoors permeates building materials. 

In terms of an HVAC contractor’s responsibilities, we can make sure drain outlets face away from the home and don’t allow water to pool against the structure. We can also do visual checks of things like exterior gutters and sump pumps—these are steps described in the thorough comfort consultation guide we made with Tim De Stasio. 

Supplemental dehumidification can help as well; there are standalone and whole-home dehumidifiers out there, and there are even ventilating dehumidifiers that can bring in fresh air as well.

Diluting VOC Concentrations with Fresh-Air Ventilation

As stated earlier, proper ventilation can help remove or dilute VOCs. Ventilation is tricky, as there are a few different things that can drive air movement into or out of the home, including fans in HVAC equipment and natural occurrences like wind or the stack effect. We can’t control nature, but we can work with the building envelope and introduce controlled ventilation pathways.

Whenever we consider ventilation, we have to be mindful of its effect on pressures. Adding ventilation with no exhaust (supply only) puts the house under positive pressure. Exhaust-only ventilation puts the house under negative pressure. Balanced ventilation (such as an HRV or ERV that tempers incoming air with stale air being exhausted) allows for a mix of positive and negative pressure. 

Too much positive pressure pushes conditioned air out, and too much negative pressure sucks air in from places like the attic (which needs to be conditioned and is often horrible to breathe in because of dust, VOCs from insulation, possible biological growth in humid climates, and more). Nevertheless, ventilation is a great tool for exhausting VOCs and/or bringing in fresh air to help dilute their concentrations.

Ventilation is a deep topic, and THIS tech tip, inspired by a livestream with Corbett Lunsford and John Semmelhack, goes into more depth. Brynn Cooksey’s 2025 HVACR Training Symposium session also has some information and tools, and it is now available to the public HERE.

Photocatalytic Oxidation (PCO) Products

The solutions we’ve discussed so far have been largely systemic; we (and/or the customer) make a major change to the home. For an HVAC technician, that change might be designing and installing a ventilation or dehumidification system. For the customer, they could change their chemical storage protocols and stop buying plug-in air fresheners. This next one is a “bolt-on” product.

Photocatalytic oxidation (PCO) products consist of a UV light inside a titanium oxide casing. They produce unstable hydroxyl radicals that bind to VOCs and (ideally) break them down into “harmless” byproducts like water and carbon dioxide. 

But water and carbon dioxide are not all that “harmless.” The chart we saw earlier shows how water vapor and moisture can lead to IAQ problems, and high levels of carbon dioxide can cause drowsiness, headaches, and impaired concentration.

It’s also worth noting that studies have shown PCO devices to produce formaldehyde and acetaldehyde (one such study is “Performance of ultraviolet photocatalytic oxidation for indoor air cleaning applications” by Hodgson AT, Destaillats H, Sullivan DP, Fisk WJ). Can you offer these products? Sure, they exist in the market, though it’s not something we recommend. The important thing is not to sell them as a silver bullet with zero potential negative byproducts. 

Carbon Filtration

Remember when we talked about adsorption? Carbon filters use this to their advantage, as VOCs will cling to the source of carbon, usually a form of charcoal. 

In these filters, media typically contains a thin layer of charcoal from heated coconut shells that is further treated with heat and exposure to other elements to become porous, which increases the surface area. This layer attracts VOCs, which cling to its surface. Unfortunately, these filters lose their efficacy quickly, and the ability to adsorb VOCs effectively lasts only a week or two.

While the science behind these filters is sound, we need to be realistic about how long they’ll maintain their efficacy, which is further degraded in humid climates.

One Final Note About Offering Solutions

VOCs can sound scary, especially when you think about the long-term health risks. That’s why we need to be tactful but honest anytime we educate our customers about things in their air that can cause health risks. Then, we need to offer a way to collect data about the problem to come up with a solution that will solve a real issue.

Our goal is to provide them with evidence and education to empower them to make choices for their own health, not scare them into purchasing a solution. That’s why monitoring and gathering sufficient data is crucial, as is focusing on holistic change rather than installing a PCO device or a carbon filter, dusting your hands off, and walking away. Even if a customer doesn’t want to pursue any HVAC or building-related upgrades, they can still make a positive difference for their health by storing cleaners in sealed bins in the garage or stopping the use of plug-in air fresheners. They just need the facts, and our job is to provide those and suggest solutions to inform the customer’s decision, not make that decision for them.