Indoor Air Quality Testing: What Is Worth Paying For
Some air quality testing answers real questions. Some of it exists to generate equipment sales. Here is the difference.
Useful indoor air quality measurements include continuous particulate monitoring, carbon dioxide as a ventilation indicator, humidity, and carbon monoxide detection. Mold testing is worth doing when there is visible growth or a known water event, but general "mold screening" that leads directly to an equipment recommendation deserves skepticism.
Start with the question you are trying to answer
Air quality testing is only useful if it answers a specific question. "Is my air bad?" is not a question with an actionable answer, and it is exactly the framing that leads to expensive equipment recommendations.
Useful questions: Why does this room smell musty? Why are my allergy symptoms worse indoors? Is this house adequately ventilated? Did the water leak last month cause a problem? Is there a carbon monoxide risk?
Each of those has a specific measurement that addresses it, and most of them are inexpensive.
Worth having
| Measurement | What it tells you | Cost |
|---|---|---|
| Carbon monoxide detector | Life safety — non-negotiable with gas appliances | Very low |
| Hygrometer (humidity) | Whether you are below 30% or above 50% | Very low |
| PM2.5 monitor | Fine particulate, useful during dust events | Low |
| CO2 monitor | A good proxy for ventilation adequacy | Low to moderate |
| Static pressure test | Whether your system can actually deliver air | Part of a service visit |
| Professional mold assessment | After visible growth or a water event | Moderate to high |
CO2 as a ventilation proxy
This one is underused and genuinely informative. Carbon dioxide itself is not usually a health concern at indoor levels, but it correlates well with how much fresh air a space is getting, because people produce it continuously.
Outdoor air runs around 420 parts per million. Indoor levels under about 800 suggest reasonable ventilation. Levels consistently above 1,200 in an occupied room indicate the space is not getting enough fresh air, which tends to track with stuffiness, drowsiness, and reduced concentration.
In a tightly built newer Valley home — particularly a home office with the door closed — readings above 1,500 are not unusual. An inexpensive monitor makes that visible, and the fix is usually a ventilation adjustment rather than an air purifier.
Mold testing, carefully
There are two very different things sold under this name.
Assessment after a known problem — visible growth, a roof leak, a condensate overflow, a slab leak — is legitimate and useful. An assessor identifies the moisture source, the extent, and what remediation requires. The moisture source is the actual problem; mold is the symptom.
General screening with no known issue is much less useful. Mold spores are present in all outdoor and indoor air everywhere. A test that finds spores has found normal conditions, and there are no established residential exposure limits to compare a result against.
The pattern to be skeptical of: a company performs free or inexpensive testing, reports a concerning result, and recommends equipment they sell. Assessment and remediation are ideally done by different parties for exactly this reason.
The HVAC-specific checks worth requesting
- Evaporator coil inspection — a wet coil with biological growth is a common indoor odor source
- Condensate pan and drain inspection — standing water is an indoor moisture source
- Return duct and air handler cabinet leakage — drawing attic air is a major dust and allergen path
- Static pressure — a system that cannot move air cannot filter it either
- Filter fit and seal — a filter with a gap around it is being bypassed
- Ventilation assessment — whether the home gets any deliberate fresh air at all
These cost nothing beyond a normal service visit and address the causes of most real residential air quality complaints in the Valley.
What we recommend to most households
Buy a carbon monoxide detector if you have any gas appliance. Buy a hygrometer. If anyone has respiratory sensitivity, add a PM2.5 monitor and possibly a CO2 monitor.
Then address the things those readings point to: filtration, return duct sealing, coil and drain condition, and humidity. Those solve the great majority of residential air quality complaints in Phoenix.
Spend on testing when you have a specific question, a known water event, or a health situation where a clinician has asked for information. Not as a general screening exercise that leads to a sales conversation.
Frequently asked
Is indoor air quality testing worth it?
When it answers a specific question — a musty smell, a known water event, a health concern — yes. General screening with no known issue is much less useful, because spores and particulate are present everywhere and there are no established residential limits to compare against.
What CO2 level is too high indoors?
Outdoor air is around 420 ppm. Under 800 indoors suggests reasonable ventilation. Consistently above 1,200 in an occupied room indicates inadequate fresh air, which tracks with stuffiness and reduced concentration. Tightly built homes with closed doors often exceed 1,500.
Should I test my house for mold?
If there is visible growth or a known water event, yes — and the priority is identifying the moisture source, since mold does not grow without it. Be cautious of free screening that leads directly to an equipment recommendation from the same company.