Indoor Air Quality Testing + Diagnostics

Why this matters

The IAQ sales conversation closes when the tech can SHOW the customer their problem with a number - particulate count, CO2 level, mold spore reading, CO concentration. Without measurement, "I think you have a dust problem" is a guess; with measurement, "your living room PM2.5 is 38 µg/m³ - that's 5x the EPA daily standard" is a diagnosis. IAQ testing is the proof step that converts the IAQ recommendation from suggestion into prescription.

The measurable IAQ parameters

Particulate (PM2.5, PM10)

• PM2.5: fine particles ≤ 2.5 µm - wildfire smoke, combustion, vehicle exhaust, fine dust
• PM10: particles ≤ 10 µm - coarse dust, pollen, mold fragments
• EPA standards: PM2.5 daily 35 µg/m³, annual 12 µg/m³; PM10 daily 150 µg/m³
• Health concern: PM2.5 penetrates deep into lungs, linked to cardiovascular + respiratory disease

Carbon Dioxide (CO2)

• Outdoor ambient: 420 ppm (2025)
• Acceptable indoor: < 1,000 ppm
• ASHRAE target: ≤ 1,000 ppm increment over outdoor
• Drowsiness/headache: 1,000 - 2,000 ppm
• Severe: > 5,000 ppm
• CO2 is the proxy for ventilation adequacy - high CO2 = inadequate fresh air

Carbon Monoxide (CO)

• 0 ppm baseline
• < 9 ppm acceptable (residential ASHRAE)
• 9 - 35 ppm - investigate combustion sources

• 35 ppm - DANGER; evacuate + investigate immediately

• CO alarms must alarm at ≥ 70 ppm for 1 hr OR ≥ 150 ppm for 10 min

Volatile Organic Compounds (TVOC)

• < 250 ppb (parts per billion) ideal
• 250 - 500 ppb - acceptable

• 500 ppb - investigate source (paint, cleaning products, off-gassing)

• 2,000 ppb - major concern

Humidity

• 30 - 60% relative humidity ideal
• < 30% - dry skin, static, mucous membrane irritation

• 60% - mold growth + dust mite proliferation

• 70% - major mold concern

Mold spores (CFU per cubic meter or per gram)

• Air vs surface samples; lab analysis required
• Result interpretation requires comparison to outdoor baseline
• Indoor / outdoor ratio of 1 - 2x normal; > 5x suggests indoor source

Radon

• < 2 pCi/L acceptable (EPA action level 4 pCi/L)

• 4 pCi/L - mitigation recommended

• Long-term (90 day+) tests vs short-term (3 - 7 day) - long-term more reliable
• See Radon Mitigation Basics

Testing tools

• Multi-gas IAQ meter: PM2.5/PM10 (laser scattering), CO2 (NDIR), CO (electrochemical), VOC (PID/MOS), temp + RH. Brands: Aeroqual, TSI Q-Trak, AirAdvice, IQAir AirVisual. Prosumer: PurpleAir, Awair, Foobot.
• Anemometer: verify ventilation rates + test supply/return balance.
• Particle counter: lab-grade 6-channel (0.3 - 10 µm); verify HEPA + MERV capture.
• Manometer: differential pressure across filters + heat exchangers; house pressure balance.
• Radon test kit: short-term 3 - 7 day or long-term 90 day alpha-track; EPA-certified lab.

On-site testing protocol

Initial assessment (30 - 60 min): customer interview (symptoms, season, renovations, pets, smokers); visual walk-thru (mold, moisture damage, dust, current filter); HVAC inspection (filter age, ductwork, returns/supplies); combustion appliance inventory.

Multi-point IAQ testing (1 - 2 hr): outdoor baseline at a screened location, then living room (occupied breathing height), master bedroom, kitchen (during cooking if possible), basement/utility, near each combustion appliance for CO specifically. Document readings + time + location.

Source isolation: high particulate (cooking spike? pets? filter?), high CO2 (ventilation inadequate), high VOC (paint, cleaning, off-gassing), high CO (combustion analysis immediately), high humidity (crawlspace, bath vent, cooking).

Report: tabulated readings vs reference levels, photos of HVAC + combustion sources, specific recommendations with cost ranges.

Mold-specific protocol

Suspect mold:

• Visible discoloration on wall, ceiling, floor (verify it's mold + not just dirt)
• Musty odor
• Customer complaints: allergy, respiratory, neurological symptoms

Air sampling:

1. Outdoor sample (control)
2. Indoor sample in suspect rooms
3. Calibrated pump @ 15 L/min for 5 min per sample
4. Bring samples to certified mold lab
5. Lab returns species + CFU count
6. Compare indoor vs outdoor; indoor > 5x outdoor of same species = indoor source

Surface sampling (when visible mold present):

• Tape lift or swab onto sterile media
• Lab identifies species

Limitations of mold testing:

• Single sample is a snapshot; spore counts vary hour-by-hour
• A clean sample doesn't rule out mold (intermittent exposure)
• Visual + moisture inspection + air sample together = diagnosis
• Most contractors are NOT mold remediation contractors; if confirmed, refer to licensed remediator + don't disturb the area

Combustion back-drafting test

Combustion appliances back-draft when combustion air supply is inadequate, house pressure is negative from exhaust fans/dryer, vent is blocked, draft inducer failed, or venting improper. Test: close all windows + doors, turn on all exhaust (bath, kitchen, dryer), measure house pressure (should not exceed -3 Pa), light each combustion appliance + observe vent draft 10 min, CO test (< 100 PPM in flue, < 9 PPM at face). Mitigate with combustion air, sealed appliances, makeup air fan, or removing offending exhaust.

Specialists + reporting

Refer out: asbestos (licensed abatement), lead paint (RRP contractor), mold remediation > 10 sq ft (licensed remediator), radon mitigation (certified), sewer gas (plumber), VOC ID (industrial hygienist). Customer reports that close: one-page summary with traffic-light per parameter, specific finding per red/yellow item, recommendation with cost range, clear next step. The report is a sales document, not a science paper.

References

• ASHRAE 62.1 + 62.2 (Ventilation for Acceptable Indoor Air Quality)
• EPA Indoor Air Quality reference levels
• AIHA + ACGIH industrial hygiene guidance
• NIOSH Pocket Guide to Chemical Hazards
• Manuall internal: Indoor Air Quality Services, Indoor Air Quality ERV HRV