Observation Log
Full Observation Table
| Location | Smoke Behavior | Severity | Notes |
|---|
How to Use the Smoke Test Calculator
Choose whether you're tracing duct leaks, checking the building envelope, or diagnosing zone pressure, and note whether the space was pressurized or depressurized during the test.
Add a card for each location tested. Describe the location, what the smoke did, and rate the severity of the leak or airflow observed.
Click Generate Summary to see a prioritized breakdown of findings, sorted by severity, ready to hand off or attach to a commissioning report.
Understanding Smoke Testing
A blower door or duct blaster test tells you how much air is leaking. It doesn't tell you exactly where. A smoke pencil or smoke stick fills that gap by making airflow visible at a specific point, letting a technician trace leaks to their actual source rather than guessing based on general knowledge of common problem areas.
How Smoke Testing Works
A smoke pencil or smoke stick releases a small, controlled stream of visible smoke, usually theatrical fog fluid or a chemical smoke source, near a suspected leak. If the building or duct system is under pressure relative to the area being tested, the smoke will either get pulled toward a leak or pushed away from one, depending on which direction air is moving. Watching how the smoke stream bends or dissipates tells you whether a leak exists at that spot and roughly how strong it is. ASTM E1186, the standard practices for locating air leakage sites in building envelopes, lists smoke generation alongside infrared scanning, pressurization or depressurization, sound, and tracer gas methods, and notes that these practices are qualitative rather than quantitative.
Choosing a Smoke Source
Smoke pencils and puffers that vaporize a glycol or glycerin fluid, and theatrical foggers that use similar fluids, produce a visible, low-hazard fog. Burning-wick smoke pens work too. Chemical smoke tubes and bottles are different: those based on titanium tetrachloride or stannic chloride react with humidity to release corrosive hydrochloric acid mist. A NIOSH assessment of smoke tubes in healthcare facilities recommends keeping the amount of smoke to the minimum needed, so use the smallest puff that shows the airflow, avoid breathing it directly, and ventilate the space afterward.
Pressurized vs. Depressurized Testing
Depressurizing the building with a blower door pulls outside air in through envelope leaks, so smoke held near a suspected gap gets visibly pulled toward it. Pressurizing does the opposite, pushing conditioned air out through the same leaks so smoke blows away from the source. Some technicians prefer pressurized testing since the outward smoke plume is easier to see and photograph for documentation, while others find depressurized testing more intuitive for tracing air intake paths.
Common Places to Check
For building envelope work, check window and door frames, electrical outlet boxes on exterior walls, plumbing and wiring penetrations, attic hatches, and the rim joist area where framing meets the foundation. For duct systems, check plenum connections, boot-to-drywall joints, and any accessible duct seams, especially in unconditioned spaces like attics and crawlspaces where duct blaster testing has already flagged higher leakage. Once the leaks are located, the air sealing savings calculator estimates what closing them is worth.
Zone Pressure Diagnostics
Smoke testing at interior doorways can reveal pressure imbalances between rooms, often caused by return air starvation when a room has supply ductwork but no dedicated return path. A door that shows smoke moving strongly under it while closed suggests a meaningful pressure difference between that room and the rest of the house, which can point to duct design issues worth investigating with the pressure decay test calculator or a full test, adjust, and balance assessment. A room with supply ductwork but no return path often needs a transfer path, and the transfer air calculator in ventilation is the place to start planning one.
Documenting Results
Smoke test findings are qualitative by nature, so clear documentation matters. Recording location, observed smoke behavior, and a consistent severity rating for each point creates a record that supports prioritizing sealing work and demonstrates due diligence for energy program or client reporting.
Frequently Asked Questions
A smoke pencil or smoke stick releases a visible stream of theatrical fog or chemical smoke near a suspected leak point, and the way the smoke moves reveals air infiltration or exfiltration direction and relative strength. It is commonly used alongside a blower door or duct blaster test to pinpoint exactly where leakage is occurring, rather than just knowing the total amount.
Either can work depending on what you're diagnosing. Depressurizing the building with a blower door pulls outside air in through leaks, making smoke get pulled toward the leak, which is useful for finding envelope leaks. Pressurizing pushes conditioned air out through leaks, making smoke blow away from the leak, which some technicians find easier to see and photograph.
No. A smoke test is a diagnostic and locating tool that shows where air is moving, but it does not quantify total leakage the way a calibrated blower door or duct blaster test does. Use a smoke test to find and prioritize individual leaks, then use the quantitative tests to confirm overall improvement after sealing.
It depends on the smoke source. Glycol-based smoke pencils and theatrical fog fluids are generally used for brief diagnostics indoors with normal ventilation, but always follow the product's safety data sheet. Chemical smoke tubes and bottles based on titanium tetrachloride or stannic chloride release corrosive hydrochloric acid mist, so keep the amount to a minimum, never breathe the smoke directly, and ventilate afterward. With any smoke source, keep it away from open flames and active combustion appliances during testing.
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