Indoor Air Quality Testing: What Is Measured, Limits, Costs

Most pages ranking for this topic sell a kit. This one pairs each pollutant with its measurement method and the published number a result is compared with, and names who wrote that number. Where no number exists, it says so.

What a professional indoor air quality assessment measures

A professional assessment is an investigation first. The sequence below is the one the OSHA Technical Manual sets out for workplaces, and its comparison logic carries over to a house: sample outdoor air, return air, and complaint and non-complaint rooms. Radon, mold and particles are added when the building or the complaint points to them.

Step	What is done	Why it matters
Interviews	Complaint pattern, HVAC upkeep, renovations	Tells the investigator where to sample
Walkaround	Ventilation survey, then indoor and outdoor sources	OSHA cites NIOSH finding ventilation the main cause in 52% of its investigations
HVAC check	Outdoor air intake at maximum and minimum flow	Separates ventilation from source problems
Screening	Direct-reading formaldehyde, CO2, CO and VOCs, plus temperature and humidity	Comparable across rooms
Follow-up	Validated lab methods for whatever screening flagged	Gives a defensible number

The OSHA indoor air quality page says OSHA has no indoor air quality standards, and EPA’s air standards are written for outdoor air. If a tester says a home ‘fails’ an indoor standard, ask which one.

Pollutant, method, reference value, source

This is the table to keep. EPA protects outdoor air, OSHA protects workers over a shift, and WHO and California publish guidelines, not enforceable limits.

Pollutant	How it is measured	Published reference value	Source
Carbon dioxide	Direct-reading sensor, logged while occupied	No limit in ASHRAE 62.1; OSHA workplace limit 5,000 ppm (8 h)	ASHRAE CO2 position document
PM2.5	Particle counter or gravimetric filter	EPA outdoor 9.0 µg/m³ annual, 35 µg/m³ 24 h; WHO 5 and 15	EPA NAAQS table; WHO 2021 air quality guidelines
Formaldehyde	Sorbent badge, lab analysis (NIOSH 2016)	WHO 0.1 mg/m³ (30 min); OEHHA 55 µg/m³ acute, 9 µg/m³ (8 h and chronic)	WHO indoor air guidelines; OEHHA REL table
Other VOCs	Canister, EPA Method TO-15	No total VOC value; WHO covers single compounds only	WHO indoor air guidelines
Radon	Radon test device	Fix at 4 pCi/L or more; consider fixing at 2 to 4	EPA radon action level page
Mold	Spore trap with outdoor control	No EPA or other federal limit	EPA mold testing page
Carbon monoxide	Direct-reading meter; UL 2034 alarm	Alarm windows at 70, 150, 400 ppm; OSHA 50 ppm (8 h); EPA outdoor 9 ppm (8 h)	UL Standards and Engagement; OSHA CO fact sheet; EPA NAAQS table
Relative humidity	Hygrometer or logger	Below 60%, ideally 30 to 50%, per the EPA; 20 to 60% in the OSHA manual	EPA moisture guidance; OSHA Technical Manual

Carbon dioxide: the limit that is not one

CO2 is the reading consumer monitors lead with and the one most often misread. The ASHRAE CO2 position document, approved on 12 February 2025, says that despite many statements to the contrary, Standard 62.1 does not provide a limit value for indoor CO2. According to ASHRAE, the 1989 edition did carry a 1,000 ppmv limit, removed later because it was misread; today that figure is at best an indicator of about 16 cfm of outdoor air per person.

One number cannot fit every room either. Per the position document, steady-state values under 62.1 run from about 1,000 ppmv in offices to above 2,500 ppmv in auditoriums, and CO2 is not a general indicator of indoor air quality. It works as a tracer: outdoor air reached 426 ppmv in 2024, according to ASHRAE citing NOAA, so a bedroom logging far above that overnight is telling you about air exchange, not about radon, CO or formaldehyde.

Particles: an outdoor standard used as an indoor yardstick

The EPA NAAQS table sets the primary PM2.5 standard at 9.0 µg/m³ as a three-year annual mean and 35 µg/m³ over 24 hours. The annual level dates from February 2024, and the EPA PM NAAQS page carries a March 2025 notice on reconsidering it. The WHO 2021 air quality guidelines recommend 5 and 15 µg/m³.

Neither is an indoor limit. The EPA indoor particle page lists cooking, candles, fireplaces, unvented heaters and smoking as indoor sources and says homes without strong sources should sit at or below outdoor levels. So read indoor PM2.5 beside a same-day outdoor reading.

Formaldehyde and other VOCs

Formaldehyde has health-based indoor reference values from both WHO and California. The WHO indoor air guidelines (2010) set 0.1 mg/m³ over 30 minutes, about 81 ppb at 25 °C on our conversion. California’s OEHHA REL table lists 55 µg/m³ acute and 9 µg/m³ for the 8-hour and chronic levels, about 7.3 ppb.

The CARB formaldehyde fact sheet names composite wood as a main source and notes that home kits can measure formaldehyde but cannot identify its source. Other VOCs are harder: the total (TVOC) many reports add has no recognised limit, and the EPA monitor guidance says most indoor pollutants lack accepted limits. Treat a VOC index as a trend.

Radon, mold, carbon monoxide and humidity

Radon

The EPA radon action level page says EPA recommends fixing at 4 pCi/L or more and considering a fix between 2 and 4, as no level is known to be safe. The EPA radon risk page puts the average home at 1.3 pCi/L. Fixes are in our radon mitigation guide. What a fix costs, from published prices, is in our guide to radon mitigation cost.

Mold

The EPA mold testing page says no federal limits exist for mold or spores and that sampling is usually unnecessary when growth is visible. Air results are read against an outdoor control, as our page on mold spores in air explains; test choice is covered in mold testing.

Carbon monoxide

According to First Alert, UL 2034 requires an alarm at 70 ppm to activate within 60 to 240 minutes. That lowest alarm point is 1.4 times OSHA’s workplace limit and 7.8 times EPA’s 8-hour outdoor standard, so a professional measures CO with a meter; the CPSC CO guidance still wants an alarm on every level.

Humidity

The EPA moisture guidance advises keeping relative humidity below 60%, ideally 30% to 50%: the cheapest number to log.

Home air quality test kits and monitors versus lab sampling

A home air quality test can mean a monitor, a mail-in kit, or a single radon or CO device. The EPA monitor guidance says there is limited information on how well some low-cost monitors detect pollutants indoors, that they detect only what they were built for, and that no indoor reference methods exist. Monitors show change; lab sampling gives a number you can show an adjuster. For mold specifically, our guide to at home mold test kits covers what each type can and cannot show.

Option	What it measures	What you get	Main limit
Consumer monitor	PM2.5, CO2, VOC index, humidity	Continuous trend	Alerts set by the maker
Single-purpose device	Radon, or CO (UL 2034 alarm)	One clear threshold	Answers nothing else
Mail-in lab kit	Formaldehyde, VOCs, mold, dust	Lab report in 5 business days, per Home Air Check	Cannot identify the source, per CARB
Professional survey	CO2, CO, formaldehyde, VOCs, particles	Room-by-room comparison	Snapshot of one visit
Professional lab sampling	Badges, TO-15 canisters, spore traps	Defensible numbers	Costs more; days to weeks

Who does indoor air quality testing

The person matters more than the instrument. The oldest credential is the Certified Industrial Hygienist; its issuer was founded in 1960 as the American Board of Industrial Hygiene and announced its new name in 2019, per the BGC history page. The BGC CIH requirements list 60 semester hours of science, 180 academic or 240 continuing-education hours of industrial hygiene, ethics coursework and an exam.

Credential or role	Issued by	What stands behind it	How to check
CIH (Certified Industrial Hygienist)	Board for Global EHS Credentialing, formerly ABIH	Science and hygiene coursework, ethics, active practice, exam	BGC Verify Credentials
CIEC and CIE	American Council for Accredited Certification	CESB-accredited; CIEC engineering-related, CIE technician level	ACAC Find Certificants
IEP	No issuer: a role defined in ANSI/IICRC S500	Education, training and experience	Ask which credential
State mold assessor licence	State agency, where one exists	Varies by state	State licence lookup
The laboratory	AIHA Laboratory Accreditation Programs	EMLAP (microbiology), IHLAP (industrial hygiene)	AIHA Find an Accredited Lab

‘IEP’ needs a warning. The ANSI/IICRC S500 definition, quoted in a February 2026 IICRC S500 statement, describes someone with the education, training and experience to design a sampling strategy and interpret lab data. It is not a credential, so anyone can use the label. Some states license mold assessment; see our state mold licensing guide.

What air quality testing costs

HomeAdvisor reports, in a guide updated 19 June 2026, that an indoor air quality test averages $443. Lab fees are the floor under any quote: according to the EMSL 2026 price list, a formaldehyde badge costs $127 to $394 per sample, depending on turnaround.

Item	Published price	Per the source
Typical indoor air quality test	$303 to $616 (average $443)	HomeAdvisor
Mold testing	$300 to $1,000	HomeAdvisor
Radon testing	$150 to $800	HomeAdvisor
VOCs, per sample	$200 to $300	HomeAdvisor
Carbon monoxide testing	$100 to $200	HomeAdvisor
Home over 2,500 sq ft	$500 to $1,000	HomeAdvisor, by size
Mail-in kits	$205 to $495	Home Air Check, four kits
Lab only: formaldehyde badge	$127 to $394	EMSL, 2 week to 1 day
Lab only: TO-15 VOC scan	$366 to $1,148	EMSL, 2 week to 1 day

Two cheap items come first. According to HomeAdvisor, CO alarms cost $15 to $150, and a hygrometer costs less than one lab sample. Mold inspection fees are in our mold inspection cost guide.

Which test fits your situation

If this is your situation	Test first	Who or what
Fuel-burning appliance, attached garage, or a CO alarm sounded	Carbon monoxide	Alarms per CPSC; a sounding alarm is an emergency, not a test
Never tested, or living space below grade	Radon	Owner test; fix at 4 pCi/L or more (EPA)
Water damage, musty odour, visible growth	Moisture and humidity first	IEP or CIH; mold air sampling rarely needed (EPA)
New cabinets, flooring or furniture	Formaldehyde, then VOCs	Lab badge; kit as a screen
Stuffy rooms, window condensation	CO2 and humidity	Monitor; read CO2 as ventilation
Wildfire smoke, wood stove, heavy cooking	PM2.5 in and out	Monitor plus outdoor data
Asbestos removal just finished	Clearance air samples	Accredited inspector and lab

The order that saves money

1. Write down the trigger: an odour, an alarm, a water event, a renovation. It decides the test.
2. Rule out carbon monoxide and radon first: clearest thresholds, cheapest devices.
3. Log humidity for a week. EPA says keep it below 60%.
4. Look for moisture and growth before paying for a mold air sample.
5. A trend needs a monitor; a dispute needs a lab.
6. If you hire, ask for the credential, a written sampling plan, an outdoor control, the lab’s accreditation and the reference value behind each result.
7. Re-test after the fix with the same method.

For contractors: air quality testing after water intrusion

On a water or mold job the air test usually belongs to someone else. ANSI/IICRC S500 puts sampling strategy and interpretation with the IEP, and an assessor independent of your firm avoids a conflict of interest. Your job is to make sure the report supports your scope, after the moisture mapping our water damage inspection guide describes.

Report element	What it should show	Why it matters
Sampling plan	Locations, durations, outdoor controls	The first question asked of any air result
Method and lab	Named method and the lab’s AIHA accreditation	Makes the number defensible
Reference value	The published value used, with its source	Stops a guideline posing as a legal limit
Independence	Who sampled, and whether they bid the work	Keeps assessment apart from remediation
Clearance	Same method and locations after the work	Before and after must compare

Asbestos has a hard federal clearance rule, for schools: under 40 CFR 763.90, removal is complete when, among other conditions, the average of five TEM air samples inside the work area is not statistically different from five taken outside. See our asbestos testing cost page and the standards hub.

Questions people actually ask

How can I test my indoor air quality at home?

Start with the two devices that have clear thresholds: a radon test and a UL 2034 carbon monoxide alarm. Add a hygrometer, since EPA advises keeping humidity below 60%. A consumer monitor adds PM2.5 and CO2 trends. Use a lab kit or a professional for formaldehyde and VOCs.

Is indoor air quality testing worth it?

Yes, when there is a specific trigger: a water event, a renovation, new cabinets, an odour, or a dispute with a landlord or insurer. A general panel with no question behind it often returns numbers with no reference value. Radon and carbon monoxide checks are worth doing in every home.

What does an indoor air quality test check for?

A professional screening, as the OSHA Technical Manual describes it, covers carbon dioxide, carbon monoxide, formaldehyde, VOCs, temperature and humidity, compared with outdoor air. Particles, radon and mold are added when the building calls for them. Each reading has its own reference value.

What are signs of poor indoor air quality?

Look at the building: window condensation, humidity above EPA’s 60% ceiling, musty odours, visible growth, stale air in occupied rooms, a sounding CO alarm, or chemical odours after a renovation. Each points to a test. How a person feels is a question for a physician.

Who offers water damage restoration with mold removal and air quality testing?

Many restoration firms offer all three, but the assessment is best done by someone independent of the remediation. Look for a CIH (check through BGC) or an ACAC credential holder, check whether your state licenses mold assessors, and ask which AIHA-accredited lab will analyse the samples. We do not rank companies.

How do I get an air test after asbestos removal is finished?

Arrange clearance testing before the work ends, using an accredited inspector rather than the abatement crew. For schools, 40 CFR 763.90 requires a visual inspection, then five TEM air samples inside compared with five outside. Homes follow state and local rules; ask your state asbestos programme.