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Indoor air can contain moisture, fine particles, chemical vapors, combustion gases, and soil gases like radon. Each requires a different way of checking, so no single observation, gadget, or test kit tells you everything about the air in your home. Here is what each method can and cannot measure, and when to bring in a professional.
How Can You Test Indoor Air Quality at Home?
You can test indoor air quality at home by checking humidity with a hygrometer, making sure certified carbon monoxide and smoke alarms are working, using an indoor air quality monitor to track particles, VOCs, or carbon dioxide, testing for radon with a radon test kit, and inspecting for moisture and possible mold sources. When readings are hard to interpret or the source of a problem is unclear, professional indoor air quality testing can help.
The key is matching the method to the concern. A particle monitor won’t detect radon, a radon kit won’t detect mold, and a general air quality monitor is not a replacement for a carbon monoxide alarm.
Signs Your Indoor Air Quality May Need Attention
These home conditions don’t diagnose a specific pollutant, but they signal that something deserves a closer look:
• Persistent musty or stale odors, especially odors that return after cleaning
• Condensation on windows, walls, pipes, or air vents
• Visible moisture problems, such as water stains, leaks, or damp materials
• Visible mold growth on walls, ceilings, cabinets, or around the HVAC system
• Dust that builds up quickly after cleaning, or dust collecting around supply vents
• Cooking or chemical odors that linger, which can point to limited ventilation
If someone in your home has health symptoms they believe are related to indoor air, talk with a health care provider. Home testing can point to possible sources, but it cannot explain a specific person’s symptoms.
7 Ways to Test Your Indoor Air Quality
1. Check Your Carbon Monoxide and Smoke Alarms
Carbon monoxide (CO) is colorless and odorless, so you cannot rely on your senses to detect it. CO alarms and smoke alarms are life-safety devices, not optional air quality gadgets. The U.S. Consumer Product Safety Commission recommends that you install CO alarms on each level of the home and outside sleeping areas and test them monthly. Choose CO alarms certified to the UL 2034 standard.
A multi-sensor air quality monitor that lists CO should not replace a certified CO alarm, because consumer monitors are not designed to warn of immediate danger.
If a CO alarm sounds, get everyone outside immediately and call 911. Do not try to locate the source yourself, and have fuel-burning appliances inspected by a qualified professional.
2. Monitor Indoor Humidity
Humidity is one of the most useful and least expensive measurements. Excess moisture supports mold growth and dust mites. The EPA recommends keeping indoor relative humidity below 60 percent, ideally between 30 and 50 percent. A basic digital hygrometer from a hardware store can measure it.
• Check humidity in more than one room, including bedrooms and any room that tends to feel damp.
• Note whether humidity stays high while your air conditioner is running.
Your AC normally removes some moisture as it cools. If humidity stays high while it runs, sizing, airflow, or ventilation may need an HVAC professional’s evaluation. Learn more about how your home’s humidity influences indoor comfort.
3. Look for Moisture and Possible Mold Sources
Mold needs moisture to grow, so finding and fixing moisture matters more than identifying the exact type of mold. Check under sinks, around tubs and toilets, near windows and exterior doors, around the indoor HVAC unit and condensate drain, and in closets with limited airflow.
If you can see mold, the EPA advises that sampling is usually unnecessary. Focus on fixing the moisture source and cleaning up or remediating the growth appropriately. There are also no federal limits for airborne mold spores. Mold testing makes more sense when there is a persistent musty odor with no visible growth, or after water damage where hidden mold is possible. Sampling should be designed and interpreted by experienced professionals.
4. Track Airborne Particles with a Monitor
Many consumer monitors measure fine particles, reported as PM2.5 and sometimes PM10. Readings show how cooking, candles, dusting, or outdoor smoke affect your air.
A monitor is most useful for comparisons. A short spike while cooking that drops quickly with the range hood on is very different from readings that stay elevated all day.
5. Watch VOC and Carbon Dioxide Readings
• VOCs come from paints, adhesives, cleaning supplies, air fresheners, and some new furnishings. Many consumer VOC sensors give a general reading and do not identify specific chemicals, so treat them as a trend indicator.
• Carbon dioxide builds up from people breathing in closed rooms. Rising CO2 can signal that a room is not getting much fresh air.
According to the EPA, there are no widely accepted indoor health-based thresholds for most pollutants these monitors measure, so alert levels are set by each manufacturer.
6. Test for Radon
Radon is a naturally occurring radioactive gas from soil that can enter homes through foundation openings. Testing is the only way to know your home’s level. According to the Florida Department of Health, about one in five Florida homes tested has radon above the action level of 4 pCi/L.
1. Place a short-term test kit in the lowest lived-in level of your home, following the kit’s instructions.
2. Send it to the lab listed with the kit.
3. If the result is 4 pCi/L or higher, follow the EPA’s radon testing and follow-up guidance, which typically involves a second test before deciding on mitigation.
7. Schedule Professional Indoor Air Quality Testing
When the steps above leave unanswered questions, professional testing can help connect readings to likely sources, especially when the HVAC system may be involved.
Which Test Matches Your Concern?
| Your concern | Best starting point | What it won’t tell you |
| Carbon monoxide from gas appliances or an attached garage | UL 2034 certified CO alarms | Other pollutants |
| Damp air, condensation, musty smells | Hygrometer readings in several rooms over several days | Whether mold is present |
| Visible mold | Fix the moisture source; sampling usually not needed | The extent of hidden growth |
| Smoke, cooking particles, dust | Monitor with a PM2.5 sensor | The type of particle |
| Chemical odors from new products or renovation | Monitor with a VOC sensor, used for trends | Which specific chemicals are present |
| Stuffy rooms | Monitor with a CO2 sensor | Levels of other pollutants |
| Radon | Radon test kit or dedicated radon monitor | Any other pollutant |
| Unclear source or conflicting readings | Professional indoor air quality assessment | Depends on the scope of testing |
What Can an Indoor Air Quality Monitor Measure?
The EPA notes that consumer monitors only detect the contaminants or conditions they are designed for, so check which sensors a device includes.
| Measurement | What it may indicate | Important limitation |
| PM2.5 / PM10 | Particles from cooking, smoke, dust, and outdoor air | Does not identify the source or type of particle |
| Relative humidity | Moisture conditions that can support mold or dust mites | Reflects only the spot where the device sits |
| VOCs (often shown as TVOC) | Emissions from household products and furnishings | Usually a general reading; does not identify specific chemicals |
| CO2 | How well a room is ventilated for the number of people in it | Does not measure other pollutants |
| Radon (dedicated or some combination models) | Radon levels over time | Follow EPA testing guidance before making mitigation decisions |
Where to Place a Monitor
The EPA suggests placing a monitor 3 to 6 feet off the floor with open air around it, away from stoves, cleaning products, open windows, and HVAC vents. One monitor may not represent your entire home.
What Can’t a Home Air Quality Monitor Tell You?
A typical consumer monitor cannot:
• Confirm or rule out mold growth
• Detect radon unless it has a dedicated radon sensor
• Replace a certified CO alarm, even if it lists CO
• Identify individual allergens such as pollen, pet dander, or dust mite allergens
• Identify specific chemicals within a VOC reading
• Tell you what a reading means for a particular person’s health
• Locate the source of a problem
A good reading only means the measured pollutants were low at that spot and time, and one high reading does not necessarily mean an ongoing problem.
When Should You Consider Professional Indoor Air Quality Testing?
Consider professional testing when:
• Humidity stays above 60 percent even with the air conditioning running
• You notice a persistent musty odor but cannot find visible mold or a moisture source
• Your home has had a leak, flooding, or other water damage
• Dust or odors seem to come from the HVAC system or vents
• You want a clearer picture before choosing indoor air quality equipment
Radon is typically handled by radon specialists. An HVAC contractor can evaluate how humidity, airflow, filtration, and your equipment affect indoor air.
Questions to Ask before You Book a Test
1. Which pollutants or conditions will be measured?
2. What equipment or sampling method will be used?
3. How will the results be explained, and what will they be compared against?
4. Will the results point to likely sources, or only to concentrations?
If your concerns involve humidity, dust, airflow, or your HVAC system, see what is included in our indoor air quality testing service.
Next Steps Based on What You Find
The right solution depends on the source: control the source first, then improve ventilation, then add filtration where appropriate. No single product solves every problem.
| What testing points to | Typical direction |
| High humidity or condensation | Fix leaks, evaluate AC performance, and consider whole-home dehumidifier installation |
| Dust and particles circulating through the home | Check filter condition and fit with AC filter replacement or consider upgraded HVAC air filtration |
| VOCs from products or renovation | Reduce or remove sources and ventilate during and after use |
| Stuffy rooms or rising CO2 | Improve fresh air ventilation |
| Elevated radon | Consult a qualified radon mitigation professional |
| Visible or suspected mold | Correct the moisture source and follow appropriate cleanup guidance |
Filtration helps only with airborne particles that pass through the filter and does not fix moisture or radon problems. For a closer look at solutions, read our guide to improving the air inside your home and our explainer on how HVAC air filtration works.
Get Clear Answers about Your Home’s Air
Simple checks often reveal the likely issue. When the source isn’t clear or seems tied to your heating and cooling system, Underwood AC can help you evaluate humidity, airflow, and filtration. Schedule an air quality assessment or explore our HVAC services to take the next step.
Indoor Air Quality Testing FAQs
Accuracy varies by device, sensor, and placement. The EPA notes limited information exists on how well many low-cost monitors perform indoors, and accuracy can differ even between models from the same brand. They are best for spotting trends.
Yes. Radon can enter through openings in a slab foundation, and the Florida Department of Health reports elevated levels in many building types, including manufactured homes and high-rise condominiums. Test the lowest level of your home that people regularly use.
Test alarms monthly and check humidity at least seasonally. Retest for radon after major renovations, and check again whenever you notice new odors, moisture, or comfort changes.