Testing
How to Test Your Indoor Air Quality (4 Steps, Starting Free)
Most people have no idea what is in their home's air. Not because it is hard to find out — a $15 kit answers the most dangerous question. Here is the full progression, from free to thorough.
April 2026 · 7 min read · By the CleanAirHomeLab team
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 | Cost | What It Finds | Time to Result |
|---|---|---|---|---|
| Step 1 | The Free Smell and Visual Check | $0 | Mold, gas leaks, VOC sources, obvious moisture | Immediate |
| Step 2 | Radon Test Kit (Mail-in) | $15 | Radon gas (the #1 cause of lung cancer in non-smokers) | 2-4 weeks total (90-day exposure + 1-2 week lab) |
| Step 3 | Budget PM2.5 + CO2 Monitor | $40-90 | Fine particles (PM2.5), CO2, temperature, humidity | Real-time |
| Step 4 | Multi-sensor Continuous Monitor | $180-229 | Radon, PM2.5, CO2, VOCs, humidity, temperature | Real-time (radon takes 7 days to stabilize) |
| Bonus | Pro Lab Test | $100-300 | Specific VOCs, formaldehyde, lead dust, asbestos | 1-2 weeks |
Step 1: The Free Check ($0)
Walk through your home slowly. You are looking for three things: smells, visible moisture, and obvious VOC sources.
- Smell:Musty = mold. Rotten egg = gas leak (call your utility company immediately). Chemical = off-gassing from new furniture, paint, or cleaning products.
- Moisture:Check under sinks, around windows, and in the basement. Dark spots, water stains, or visible mold are immediate red flags.
- VOC sources:Recent paint, new carpet, air fresheners, cleaning products stored under the sink. Every one of these releases VOCs into your air.
This step costs nothing and takes 10 minutes. It does not give you numbers, but it tells you where to focus.
Step 2: Test for Radon ($15)
Radon is the one pollutant most people have never thought about — and the one most worth testing for first. It is radioactive gas that seeps from the ground into your basement and living areas. No smell. No color. No warning.
The numbers that matter:
- Below 2 pCi/L: You are fine. Retest every 2 years.
- 2-4 pCi/L: Consider mitigation. The WHO action level is 2.7 pCi/L.
- Above 4 pCi/L: EPA action level. Get a certified mitigation contractor.
The RadonAway long-term test kit costs $15 on Amazon. You place it in your lowest lived-in floor for 90 days, mail it in, and get lab-certified results. If your result is above 4 pCi/L, the fix (a mitigation system) costs $800-2,500 — but it solves the problem permanently.
Once you know your baseline, a continuous monitor like the Airthings Wave Plus ($229) lets you track radon over time — useful after mitigation to confirm it is working.
Step 3: Monitor PM2.5 and CO2 ($40-90)
Particles and carbon dioxide are the two pollutants most likely to be elevated in a typical home. Both have real effects on how you feel and how well you think.
PM2.5 (Fine Particles)
PM2.5 are particles smaller than 2.5 microns — fine enough to get deep into your lungs. Sources include cooking, candles, incense, traffic pollution seeping in, and wildfire smoke. The Govee H5179 (~$40 on Amazon) is the most cost-effective entry-level PM2.5 monitor with WiFi and an app.
| PM2.5 Level (ug/m3) | Category | What to Do |
|---|---|---|
| 0-12 | Good | No concern. Air quality is clean. |
| 12-35 | Moderate | Sensitive groups may notice effects. |
| 35-55 | Unhealthy for Sensitive Groups | Run your purifier. Close windows. |
| 55-150 | Unhealthy | Reduce time indoors. Purifier on high. |
| 150+ | Very Unhealthy | Stay inside. Purifier at maximum. Seal gaps. |
CO2 (Carbon Dioxide)
CO2 above 1,000 ppm causes measurable drops in cognitive performance — slower thinking, harder to concentrate. It builds up fast in bedrooms with closed doors overnight. The AirGradient ONE ($90 direct at airgradient.com) uses a true NDIR CO2 sensor, which is the gold standard for accuracy. Budget monitors use estimated CO2 and are often wrong.
| CO2 Level (ppm) | Category | What to Do |
|---|---|---|
| 400-600 | Outdoor baseline | Normal. Good ventilation. |
| 600-800 | Acceptable | Fine for most spaces. |
| 800-1000 | Getting stuffy | Open a window if possible. |
| 1000-1500 | Poor | Noticeable cognitive effects. Ventilate now. |
| 1500+ | Unhealthy | Serious ventilation problem. Investigate HVAC. |
Step 4: Get the Full Picture ($229)
If you want one device that covers radon, CO2, VOCs, humidity, temperature, and air pressure, the Airthings Wave Plus ($229) is the only consumer monitor that does all of that. It runs on two AA batteries and mounts anywhere — including your basement where radon testing matters most.
The key limitation to know: the Wave Plus does not have a PM2.5 sensor. For particle tracking, you still need the Govee or an AirGradient. If you want everything in one device including PM2.5, step up to the Airthings View Plus ($299), which adds a particle sensor and a built-in display.
We link to Airthings.com directly (not Amazon) because they offer 25% commission, which helps keep this site free. The price is the same either way.
What to Do When You Find Something
High radon (above 4 pCi/L)
Call a certified radon mitigation contractor. A sub-slab depressurization system ($800-2,500) vents radon outside before it enters your living space. This is a permanent fix, not a filter.
High PM2.5
Find the source first. If it spikes when you cook, run your range hood and crack a window. If it is elevated all day, check your HVAC filter and run an air purifier. See our air purifier guide for picks by room size.
High CO2 (above 1,000 ppm)
Open windows and doors to ventilate. If it stays high with windows open, you have a ventilation system problem — your HVAC may not be bringing in enough fresh air. An HVAC technician can check your fresh air intake settings.
High VOCs
Identify and remove the source: new furniture, paint, cleaning products, or air fresheners. Ventilate heavily for 24-72 hours after painting or installing new flooring. An activated carbon air purifier helps while the off-gassing period runs its course.
Common Questions
What is the most important thing to test for in your home?
Radon. It has no color, no smell, and no taste. The only way to find it is to test for it. Radon is the second leading cause of lung cancer in the US — about 21,000 deaths per year. The EPA estimates 1 in 15 homes has radon levels at or above the 4 pCi/L action level. A $15 mail-in kit tells you whether you have a problem. Start there before spending money on anything else.
Do I really need a monitor if I have an air purifier?
Yes, and here is why. An air purifier removes particles from the air. A monitor tells you whether it is working, what the levels were before and after, and whether there are problems the purifier cannot fix. CO2 is not a particle — a purifier does not reduce it. Radon is not a particle — a purifier does not reduce it. You could run a $300 purifier in a basement with high radon and feel like you are doing something while the radon level stays unchanged. A monitor tells you the truth.
Can I just use a cheap $25 sensor from Amazon?
For general awareness, yes. For making decisions about mitigation or health interventions, no. Cheap sensors are useful for spotting trends — if PM2.5 spikes when you cook or when traffic is heavy, that is real information. But accuracy varies wildly. Some cheap monitors read 50-100% higher than the actual level. The Govee H5179 ($40) is reasonable for PM2.5 and temperature. For CO2, you need a true NDIR sensor — the AirGradient ONE ($90) uses one. For radon, there is no cheap accurate option below $150.
How often should I test for radon?
Run an initial long-term test (90 days). If it comes back below 2 pCi/L, test again every 2 years or after major renovations that affect your foundation. If it comes back between 2-4 pCi/L, retest and consider mitigation. If it reads above 4 pCi/L, get a continuous monitor and call a certified mitigation contractor. The EPA action level is 4 pCi/L, but the World Health Organization recommends action above 2.7 pCi/L.
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