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08 · Environmental hazard

Air pathways.
Follow the flow.

How air moves through a home can shape which pollutants enter and where they travel. Explore pressure differences, ventilation, and the small pathways that connect your living space to the outdoors and the ground below.

Know what to look for ↓Find your next step ↗
Understand the signsExplore your options

You can take this one step at a time.
Start with what you notice.

AirflowYour homePressurePathwaysClarityYour next step

A place to begin

Understand the space.
Notice the patterns.

A guide to the building, the symptoms, and the questions worth asking.

01

Understand airflow

The sources, pathways, and questions behind this topic.

↗02

Notice the signs

What to look for in your home and your daily patterns.

↗03

Explore testing

What different methods measure—and their limits.

↗04

Take the next step

Document, investigate, and get the right support.

↗

What It Is

How air moves through a home

A home is not a sealed container — it breathes. Air moves continuously between the interior, the exterior, and the ground below through pressure differences, temperature gradients, and structural gaps.

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Temperature differences, wind, and mechanical systems all affect air movement. During cold weather, warm air escaping higher in a building can draw replacement air through lower openings—the stack effect.

Exhaust fans, dryers, and range hoods remove air. Without suitable replacement air, they can increase depressurization. Unbalanced HVAC airflow may create pressure differences between rooms.

A pathway does not prove a pollutant is present. Evaluate the source, route, and actual concentrations together.

Why It's Missed

Invisible dynamics, diagnostic gaps

A routine inspection may not include pressure diagnostics or contaminant sampling. Equipment can function while whole-house airflow still needs evaluation.

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Ask what an assessment covers: leakage, room pressures, ventilation, combustion safety, and pollutant-specific testing each answer a different question.

A building-performance professional can connect findings across the home and coordinate with HVAC, radon, or environmental specialists when needed.

Commonly reported symptoms

What people notice.

Symptoms have many possible causes. The pattern can support a conversation with a clinician; it does not identify a pollutant or establish a diagnosis.

Recurring headachesFatigue / low energyDizziness / lightheadednessNauseaRespiratory irritationCognitive slowing / brain fogSinus symptomsShortness of breath

Key Concepts

Small pathways.
Connected spaces.

Six mechanisms that move pollutants through your home. Use these clues to guide the questions you ask.

01

Stack effect

Warm air rises and escapes through upper levels, pulling outside and soil air inward through lower parts of the home — strongest during colder weather.

02

Negative pressure

When exhaust or leakage lowers indoor pressure, replacement air can enter through available openings. Depending on the building and surroundings, that may include soil-air pathways.

03

Radon entry

A naturally occurring radioactive gas that enters through foundation cracks, sump pits, slab gaps, and utility penetrations.

04

HVAC imbalance

Uneven airflow can create pressure differences, causing some rooms to pull air from unintended places — including basements, crawlspaces, and foundations.

05

Combustion backdrafting

Furnaces, water heaters, fireplaces, and exhaust systems can pull combustion gases back into the home instead of venting outdoors.

06

Soil gas pathways

Radon is not the only gas that can enter a home. Methane, hydrogen sulfide, VOCs, and other soil gases may travel through the same pathways.

How to test

Different tools.
A fuller picture.

No single test tells the full story. Combine the history of the home, appropriate testing, and a qualified inspection. View the methods and how they fit into a full assessment.

01

Radon testing

Measure radon concentration over time.

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Use an appropriate radon test according to its instructions. Tests lasting more than 90 days better represent the annual average; alpha-track and certain electret devices are common long-term methods. Charcoal kits are generally short-term.

EPA recommends fixing homes at 4 pCi/L or higher and considering reduction between 2 and 4 pCi/L. Follow the recommended confirmation and mitigation process. A radon result does not measure other soil gases.

02

Blower door test

Locate leakage under controlled pressure.

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A calibrated fan measures building air leakage under controlled pressure. Combined with suitable tracing tools, it can help locate leakage routes.

Use a qualified professional who accounts for combustion appliances and other safety conditions before depressurizing the building.

03

HVAC supply / return balance

Check airflow and pressure between rooms.

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An HVAC technician with a flow hood can measure supply and return airflow in each room to identify imbalances depressurizing specific areas.

Correcting imbalances often involves adding transfer grilles, returns, or adjusting dampers.

04

Combustion safety testing

Evaluate how appliances vent under real conditions.

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A qualified professional can assess draft, spillage, and combustion under relevant operating conditions, including depressurization. This is particularly important for naturally drafted appliances.

Do not recreate worst-case conditions yourself. If a CO alarm sounds or poisoning is suspected, leave and call emergency services.

05

Professional airflow tracing

See where air moves with appropriate tools.

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A professional can use suitable smoke pencils, pressure measurements, or other tracing tools to examine air direction under the test conditions.

Do not use incense, flames, or smoke to investigate a suspected gas leak. Avoid adding irritants to sensitive households. A tracing result identifies movement, not the identity or concentration of pollutants.

What to do next

Start small.
Take the next step.

Use this checklist to organize what you’ve documented, discussed, or arranged. Address urgent safety concerns first.

  • Use an appropriate test. Follow placement, duration, and follow-up instructions.
  • Act on the result. Consult a qualified radon professional about elevated levels and mitigation.
  • Document visible gaps. Note penetrations, foundation cracks, and sump covers without entering hazardous spaces.
  • Plan repairs in context. Sealing alone is not a reliable radon remedy; coordinate with ventilation and mitigation work.
  • Use a qualified technician. Request draft, spillage, and combustion safety checks where relevant.
  • Maintain working CO alarms. Direct-vent equipment reduces some risks but still needs proper installation and maintenance.
  • Describe room patterns. Note unusual door resistance, persistent drafts, and changes when systems run.
  • Measure before adjusting. Have supply, return, and room pressures evaluated professionally.
  • Ask about scope. A building-performance assessment may combine leakage, ventilation, HVAC, and combustion checks.
  • Add specific tests as needed. Airflow testing does not identify every pollutant.
  • Retest what matters. Confirm radon mitigation and reassess affected safety or airflow conditions.
  • Save the baseline. Keep results, repair dates, and follow-up recommendations together.

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Keep exploring

A little more clarity.

CHRONICALLY EXPOSED · RESOURCE

Read the full article on small air pathways

How tiny gaps and pressure shifts move air — and contaminants — through a home.

Explore resource ↗

CHRONICALLY EXPOSED · RESOURCE

Download the home airflow checklist

Walk through airflow, pressure, and the gaps where air moves room to room.

Download checklist ↓

Further guidance: EPA · Radon · EPA · Indoor air

Explore other exposure & health topics
Carbon monoxide ↗Natural gas leak ↗Sewer gas ↗Plumbing / ventilation ↗Chemicals / VOCs ↗Water quality ↗Air pathways ↗MCAS ↗POTS / dysautonomia ↗Chronic fatigue ↗Immune dysregulation ↗Neurological ↗Respiratory ↗Musculoskeletal ↗Detox pathways ↗

A quiet first step

Understand the air.
Follow the pathways.

Start with the relevant pollutant test and a clear question about the building. Radon testing measures radon; pressure diagnostics help explain air movement. Together, they can inform the next step.

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