Testing
How to Test Your Indoor Air Quality (4 Steps, Starting Free)
Most people have no idea what is in their home's air. It is not hard to find out. A radon test kit answers the most important question. Here is the full plan, from free to thorough.
Last updated October 2026 · 7 min read · By the CleanAirHomeLab team
This page explains home air testing. It is not medical advice.
The 4-Step Testing Ladder
You do not have to do all four steps. Start at the bottom. Move up only if you want more data or have a specific concern.
| Step | Method | What It Finds | Time to Result |
|---|---|---|---|
| Step 1 | Free smell and look check | Damp spots, mold you can see, musty smells, things that give off VOCs | Right away |
| Step 2 | Radon test kit | Radon gas | EPA: short-term kits stay out 2 to 90 days, long-term kits more than 90 days. Then the lab reads it. |
| Step 3 | PM2.5 or CO2 monitor | Fine particles (PM2.5), temperature, humidity. Some also read CO2. | Live readings |
| Step 4 | Multi-sensor monitor with radon | Radon, CO2, VOCs, humidity, temperature, air pressure. Some add PM2.5. | Airthings says CO2 and VOC readings settle in about 7 days |
Step 1: The Free Check
Walk through your home slowly. You are looking for three things: smells, damp spots, and things that give off VOCs.
- Smell:A musty smell can point to damp or mold. A chemical smell can come from new furniture, paint or cleaners. If you smell gas, leave the home and call your gas utility from outside.
- Moisture:Check under sinks, around windows and in the basement. The EPA says the key to mold control is moisture control. It says to dry wet areas within 24 to 48 hours and keep indoor humidity below 60 percent, ideally 30 to 50 percent.
- VOC sources:The EPA says paints, varnishes and wax contain organic solvents, as do many cleaning, cosmetic and hobby products. Note where these are stored and used.
This step costs nothing. It does not give you numbers, but it tells you where to look.
Step 2: Test for Radon
Radon is a gas most people never think about, and the one most worth testing for first. The EPA says it is the number one cause of lung cancer among non-smokers. You cannot see it or smell it. The EPA says nearly 1 out of every 15 US homes is estimated to have high radon levels.
What the EPA says about your result:
- 4 pCi/L or more: fix your home.
- Between 2 and 4 pCi/L: consider fixing.
- Any result: it is a good idea to retest every two years.
The EPA says to place the kit in the lowest lived-in level of the home. There are two kinds. A short-term kit stays out 2 to 90 days. A long-term kit stays out more than 90 days and is more likely to show your year-round average.
- Short-term example:First Alert's RD1 is a charcoal kit you leave out for two to four days and mail in. First Alert says lab fees are included (not New Jersey state fees) and results come 3 to 5 business days after the lab gets it.
- Long-term example:RadonAway's Alpha Track stays out 91 days to one year. RadonAway says results usually come 2 to 4 weeks after the lab gets it.
If your result is high, see what radon mitigation costs. Once you know your baseline, a monitor like the Airthings Wave Plus lets you track radon over time. That helps after a fix, to confirm it is working.
Step 3: Monitor PM2.5 and CO2
Particles and carbon dioxide are the two readings most home monitors track. They tell you different things.
PM2.5 (Fine Particles)
The EPA says PM2.5 are particles generally 2.5 micrometers and smaller. It says some particles this small can get deep into your lungs, and some may even get into your bloodstream. Smoke from fires is one source the EPA names. At home, watch what makes the number jump, like cooking or candles. Govee's H5106 is one low-cost option. Govee says it reads PM2.5, temperature and humidity, runs on USB-C power, and connects over Wi-Fi and Bluetooth.
| PM2.5 (ug/m3) | EPA AQI Category |
|---|---|
| 0.0 to 9.0 | Good |
| 9.1 to 35.4 | Moderate |
| 35.5 to 55.4 | Unhealthy for Sensitive Groups |
| 55.5 to 125.4 | Unhealthy |
| 125.5 to 225.4 | Very Unhealthy |
| 225.5 and up | Hazardous |
These are the EPA's 2024 PM2.5 breakpoints for its daily outdoor Air Quality Index. A reading from a home monitor is not an official AQI, so use them as a rough guide. See what an AQI number means.
CO2 (Carbon Dioxide)
CO2 is mostly a sign of how much fresh air a room gets. People breathe it out, so it builds up in a closed room. ASHRAE says its ventilation standard, 62.1, does not set a limit for indoor CO2. A 1,000 ppm limit was in the 1989 edition and was later removed. ASHRAE also says the evidence that CO2 itself affects health, sleep or work at common indoor levels is inconsistent. If the number keeps climbing, open a window. The AirGradient ONE uses an NDIR CO2 sensor that AirGradient rates from 0 to 10,000 ppm. It also reads PM2.5, TVOC and NOx.
A CO2 monitor is not a carbon monoxide alarm. See CO detector vs CO2 monitor.
Step 4: Get the Full Picture
If you want one device for radon, CO2, VOCs, humidity, temperature and air pressure, look at the Airthings Wave Plus. Airthings says it runs on two AA batteries and connects by Bluetooth, or through an Airthings hub. That makes it easy to put in a basement, where the EPA says to test for radon.
The Wave Plus has no PM2.5 sensor and no screen, just a colored glow ring. For particles too, the Airthings View Plus adds a PM2.5 sensor, a 2.9 inch ePaper screen and Wi-Fi. Airthings' own site lists the Wave Plus at $249.99 and the View Plus at $329.99.
What to Do When You Find Something
High radon (4 pCi/L or more)
The EPA says to fix your home. It says your state radon office can give you names of qualified or state certified radon contractors. A radon fix vents the gas. It is not a filter.
High PM2.5
Find the source first. If it jumps when you cook, run your range hood. If it stays high, check your HVAC filter. The EPA says to choose at least MERV 13, or as high as your system allows. Then pick a purifier with a CADR big enough for the room. See our air purifier guide for picks by room size.
CO2 that keeps climbing
Open windows and doors to let fresh air in. If it stays high with windows open, your HVAC may not be bringing in enough outdoor air. An HVAC technician can check the fresh air intake.
High VOCs
Find and remove the source, like new furniture, paint, cleaners or air fresheners. The EPA says to increase ventilation when you use products that give off VOCs. The EPA also says activated carbon works in an air cleaner when a large amount is used.
Common Questions
What is the most important thing to test for in your home?
Radon. You cannot see it or smell it, so a test is the only way to know. The EPA says radon is the number one cause of lung cancer among non-smokers and causes about 21,000 lung cancer deaths every year. It says nearly 1 out of every 15 US homes is estimated to have high radon levels. The EPA says to fix your home at 4 pCi/L or more. A test kit tells you where you stand. Start there.
Do I really need a monitor if I have an air purifier?
It helps. A monitor shows you the numbers before and after, and it can show problems a purifier cannot fix. The EPA says the CADR rating system is for particles only. CO2 is a gas, and radon is a gas. A particle filter is not built to fix either one. A monitor tells you which problem you have.
Can I just use a cheap sensor from Amazon?
For spotting trends, a low-cost PM2.5 monitor can help. If the number jumps when you cook or when smoke drifts in, that tells you something. Govee's H5106 reads PM2.5, temperature and humidity, but Govee publishes no accuracy figure for it. For CO2, look for an NDIR sensor. The AirGradient ONE and the Airthings Wave Plus and View Plus all use one. For radon, use a radon test kit or a radon monitor.
How often should I test for radon?
The EPA says it is a good idea to retest every two years. It also says to retest on a lower level if you start living there, like a basement. A long-term test (more than 90 days) is more likely to show your year-round average than a short-term one. The EPA says to fix your home at 4 pCi/L or more, and to consider fixing between 2 and 4 pCi/L.
Keep Reading
Sources and last review
Specifications on this page are taken from the documents below, on the dates shown. We do not physically test products; read our methodology. Page last reviewed .
Correction, October 2026: this page named the Govee H5179 as a PM2.5 monitor. Govee sells the H5179 as a temperature and humidity sensor; its PM2.5 monitor is the H5106. The page also used the pre-2024 PM2.5 breakpoints, a 1,000 ppm CO2 limit ASHRAE does not set, a WHO radon figure, kit and lab prices, and a claim that Airthings pays this site a commission. All of those were corrected or removed.
- US EPA (Health Risk of Radon, re-read) (government), retrieved 2026-10-06
- US EPA (A Citizen's Guide to Radon, EPA 402/K-12/002) (government), retrieved 2026-10-06
- US EPA (government), retrieved 2026-09-03
- First Alert (manufacturer), retrieved 2026-09-04
- RadonAway (manufacturer), retrieved 2026-09-04
- US EPA (A Brief Guide to Mold, Moisture and Your Home) (government), retrieved 2026-10-05
- US EPA (Volatile Organic Compounds' Impact on Indoor Air Quality) (government), retrieved 2026-10-06
- US EPA (Particulate Matter Basics, health line) (government), retrieved 2026-10-06
- US EPA (Final Updates to the AQI for Particulate Matter, fact sheet, February 2024) (government), retrieved 2026-10-06
- ASHRAE (Position Document on Indoor Carbon Dioxide) (standards body), retrieved 2026-10-06
- Govee (Smart Air Quality Monitor, model H5106) (manufacturer), retrieved 2026-10-06
- AirGradient (manufacturer), retrieved 2026-09-03
- Airthings (Wave Plus product page, re-read) (manufacturer), retrieved 2026-10-06
- Airthings (View Plus product page, re-read) (manufacturer), retrieved 2026-10-06
- US EPA (Guide to Air Cleaners in the Home) (government), retrieved 2026-10-04
- US EPA (What is a MERV rating?) (government), retrieved 2026-10-04
Affiliate Disclosure:Some links on this page are affiliate links and may earn us a commission at no extra cost to you. As an Amazon Associate I earn from qualifying purchases. Links to Airthings, Govee or AirGradient's own sites pay us nothing. Our picks are based on the makers' published figures, not commission rates. Full disclosure.