How to test your home for air leaks with a smoke pen

Air leaks can be difficult to locate because they may be hidden above ceilings, behind trim or beneath floorboards. A smoke pen offers a quick visual check: place it near a suspected gap and watch whether moving air draws the smoke into or out of the building.

The method is most effective when there is a pressure difference between the inside and outside of the house. It is also useful for finding draughts around doors and windows, weak seals around roof penetrations and gaps where pipes, cables or ducts pass through walls.

For Australian households, smoke testing can reveal why heated or cooled rooms feel inconsistent. It is a practical first step rather than a precise measurement, so it should be combined with careful inspection and, where necessary, professional testing.

Read what the smoke is telling you

Smoke makes air movement visible. If it streams steadily through a gap, the building is under pressure and air is leaking along that route. Smoke travelling towards an opening from another part of the room may instead indicate air movement created by temperature differences, wind or an operating exhaust fan.

Leakage caused by wind will usually change direction as the outdoor conditions change. Infiltration may be strongest during cold or hot weather, while exfiltration through upper floors can occur because warm indoor air rises. Repeating a test under different conditions helps distinguish these effects from a permanent gap.

A smoke pen is a qualitative diagnostic tool rather than an air-leakage meter. It shows where to investigate but does not calculate the volume of air leaving the home. A professional blower-door test provides measured pressure and flow data that can be compared with relevant performance targets.

Prepare the house and the smoke pen

Choose a dry, calm day when outdoor smoke or strong winds will not obscure the results. Bushfire smoke, coastal gusts and dust can make the test unreliable. Before beginning, inspect the area for open flames, hot surfaces, combustible materials and operating combustion appliances.

Use a purpose-built, non-toxic building-diagnostics smoke pen and follow its instructions. Do not improvise with candles, incense, aerosol insecticide or smoke-producing chemicals. Keep the device away from children and pets, avoid direct inhalation and wash your hands after handling it.

Smoke can trigger residential smoke alarms. Ask another person to monitor the alarms, silence them only for the shortest possible period and restore them immediately. Test the alarms separately with a manufacturer-approved alarm tester rather than using the smoke pen. Keep a phone, notebook, camera and marker ready to record each finding.

Create airflow that exposes the leaks

The simplest approach is to make the house slightly depressurised. Close exterior doors and windows, block internal doorways where practical and turn off heating, cooling and combustion equipment. Running bathroom or kitchen exhaust fans can then draw air from the living areas towards those outlets.

Never create strong negative pressure while a gas heater, gas cooktop or open fireplace is operating, as this can interfere with combustion or cause backdrafting. Check appliance instructions and leave a licensed gas fitter to assess suspected appliance or flue problems. Do not block a chimney, vent or combustion-air opening during testing.

The reverse approach is to pressurise the house gently and watch for smoke escaping outwards. A blower door can do this accurately, while some people use a suitable fan and temporary doorway seal. If cooling is running during the test, a programmable controller can help prevent needless energy use; seasonal thermostat guidance explains its summer use.

Work around the building envelope

Begin near the top of each room, where rising warm air can reveal leaks, and move gradually downwards. Hold the smoke pen a few centimetres from suspected joints rather than pointing it directly into a large gap. Watch from several angles so the direction of the smoke remains visible.

Check window and door edges, wall-to-ceiling junctions, skirting, architraves, cornices, roof eaves, skylights, downlights, electrical sockets and plumbing penetrations. Also inspect exhaust hoods, bathroom vents, cabinetry and the edges of concrete slabs. In attic spaces, look for daylight around roof access hatches and service penetrations.

Mark every location that draws smoke, add a short note and take a photograph when convenient. A gap that produces only a brief puff may be affected by a nearby fan or temperature difference. Switch the fan off, change the pressure and test again before deciding whether it represents significant leakage.

Focus on common Australian weak points

Melbourne’s rapid cool changes, Sydney’s hot summers, Brisbane’s humidity and Hobart’s cold winters can all alter air movement. Repeat smoke tests on a mild, still day and, if possible, during another season. Air that leaks into a humid house can contribute to condensation, while incoming hot air places extra demand on cooling.

Brick veneer, masonry and metal-roofed homes have different vulnerable junctions. Look closely around brickwork cracks, mortar joints, roof flashing, metal roof penetrations and eaves. Ceiling insulation may conceal gaps around downlights, bathroom exhaust ducts and service pipes, while renovations are common sources of poorly sealed openings.

Hardware chains such as Bunnings and Mitre 10, together with independent building suppliers, carry or can order sealants, weather strips and diagnostic products, although availability varies by store. Australian homes commonly use ducted reverse-cycle systems, split systems or evaporative cooling, and occupants often close up rooms during winter or summer. Those habits can make leaks more noticeable.

New residential construction must satisfy the National Construction Code’s energy-efficiency and sealing provisions, but an existing household has no single smoke-pen pass mark. Rental repair duties also differ between jurisdictions: Victoria’s Residential Tenancies Act 2008 and NSW’s Residential Tenancies Act 2010 provide examples. A draught is not automatically a serious defect, but persistent damp, mould or an unsafe appliance should be reported to the landlord in writing.

Confirm the important findings

Repeat each test after changing the fan direction or pressure condition. If a leak appears only in one setup, note how wind, temperature or exhaust airflow affects it. This information helps a trade determine whether the correct solution is weatherstripping, sealing, ventilation changes or a more substantial repair.

Infrared cameras can help locate temperature differences associated with leakage, although they do not prove that a cool area is an air leak. A moisture meter can identify damp-related problems after leakage has been found. Both are useful supporting tools rather than substitutes for seeing smoke move through a gap.

Prioritise safety findings before comfort and energy issues. Combustion flues, gas appliances, electrical penetrations and water damage need qualified attention. Photograph the location, describe the symptom and arrange appropriate testing. A clear record of airflow direction and affected rooms will make quotes and repair decisions much more precise.

Repair, retest and take the next step

Common repairs include fitting door weather strips, renewing window seals, sealing suitable wall and ceiling joints and closing gaps around service penetrations. Select the sealant for the material and location, and use fire-rated products where required. Flexible glazing compounds and tapes may be more suitable than rigid filler for moving window components.

Do not seal weep holes, subfloor vents, roof ventilation or combustion-air paths merely to eliminate smoke. Air-sealing work must preserve the ventilation required by the building and its heating or cooling equipment. Once repairs are complete, repeat the smoke test from the same locations and record whether the airflow has changed.

For widespread leakage, difficult access or a suspected building defect, arrange a professional blower-door test and obtain advice from qualified tradespeople. Choose one room, test it on the next calm day and document the findings before undertaking repairs. For further reading, visit ComfortGuard comfort resources and book the appropriate professional work wherever the diagnosis identifies safety, access or structural concerns.