Use this room-by-room checklist to test whether your home ventilation is moving air as intended, identify simple faults, record repeatable readings and recognise when commissioning or compliance testing should be carried out by a qualified professional.
Overview
Testing ventilation airflow is more useful than simply checking whether a fan makes a noise. A fan can run while its grille, filter, duct or external termination is restricted. Similarly, an air inlet may look clean but provide little useful airflow if the system is incorrectly balanced or the room has no effective transfer path.
A sensible home ventilation airflow test has three levels:
- Visual and functional checks: confirm that fans, grilles, inlets, controls and external terminals are present, clean and operating.
- Simple indicative checks: use tissue, a smoke pencil designed for ventilation work or a suitable airflow instrument to confirm direction and movement. These checks are useful for fault-finding, but do not prove compliance.
- Measured commissioning: record airflow at each relevant terminal using calibrated equipment and compare the results with the system design, manufacturer instructions and applicable UK requirements.
Before testing, write down the property address, date, weather conditions, system type and any recent changes. Note whether windows and internal doors are open or closed, and use the same arrangement when repeating the test. For wider indoor air quality checks, see Indoor Air Quality at Home: What to Measure and How to Improve It.
Do not remove electrical covers, alter fan speed settings or disconnect ductwork unless you are competent to do so. Turn off the power before cleaning or inspecting components where the manufacturer requires it.
Checklist by scenario
1. Bathroom or shower-room extractor fan
- Switch the fan on using its normal control. If it has a timer or humidity function, allow the control to respond according to the manufacturer’s instructions.
- Check that the grille is not blocked by dust, paint or a recently fitted cover.
- Inspect the external wall or roof terminal from a safe position. Look for nests, leaves, lint, ice or a stuck flap.
- With the fan running, use a single sheet of light tissue as an indicative check. It should be drawn towards an extract grille rather than pushed away. This does not measure the volume of air.
- Check that air can enter the room when the door is closed. A sealed door, blocked undercut or missing transfer grille can restrict extraction and cause noise.
- Record whether the fan starts promptly, runs at the expected speed and continues for the intended overrun period.
For a measured test, use a suitable capture hood or airflow meter at the grille. Keep the instrument sealed around the terminal without pressing against or obstructing it. Record the result with the fan operating in its normal commissioned mode, then compare it with the installation documents or manufacturer’s stated requirement.
2. Kitchen extractor or cooker hood
- Identify whether the hood recirculates air through a filter or extracts outdoors. A recirculating hood cannot be tested as an external extract system.
- Inspect grease filters and replace or clean them as directed. A loaded filter can reduce airflow and increase noise.
- Check the duct route for crushed flexible duct, unnecessary bends, loose joints and an unsuitable external terminal.
- Run the hood at the normal cooking setting, not only its temporary boost setting, and record which setting was used.
- Check that replacement air can enter the kitchen without creating excessive draughts elsewhere.
Do not hold a handheld vane anemometer directly against a small grille and treat the displayed speed as the room’s airflow. Air velocity varies across the grille, and the result must be related to the open area and the instrument’s method. A capture hood or professional test is more appropriate where the result is being used for handover, remedial work or compliance evidence.
3. Continuous mechanical extract ventilation
For a centralised or decentralised continuous extract system, test every extract terminal in kitchens, bathrooms, utility rooms and other rooms served by the design. Check the normal setting first, followed by any boost setting. Record the terminal location, setting, measured airflow, instrument and any unusual noise.
Inspect the central fan, filters, accessible ductwork and external discharge point. Compare the total extract airflow with the system design rather than judging one grille in isolation. A low reading at one terminal may be caused by balancing, duct resistance or a fan setting rather than a failed grille.
4. MVHR system
MVHR requires both extract and supply terminals to be considered. Extract terminals are normally found in wet rooms and kitchens; supply terminals commonly serve bedrooms and living areas. Do not close or move terminals before testing, and do not adjust balancing dampers without recording the original position.
- Check filters, condensate drainage, fan operation and control settings.
- Confirm that each terminal is labelled in the commissioning sheet or system documentation.
- Measure supply and extract airflow at each terminal using appropriate equipment.
- Record the normal and boost modes separately where both are provided.
- Check that the overall system balance and individual room airflows match the design information.
MVHR commissioning is not the same as a basic tissue test. If the system has never been commissioned, has been altered or is causing condensation or persistent noise, arrange a qualified ventilation professional to test and rebalance it.
5. PIV or whole-house air inlet
A positive input ventilation system is assessed differently from an extractor fan. Start by checking the unit’s filter, fan operation, controller setting, duct route and discharge grille. Confirm that the inlet is unobstructed and that air can move from the input area through the home and out through suitable rooms and leakage or designed ventilation paths.
Use the manufacturer’s commissioning information as the reference for fan settings. A handheld airflow reading at a PIV diffuser may not represent the system’s total performance, particularly where the diffuser is designed to distribute air over a wide area. If condensation remains, ask for a system assessment rather than increasing the fan speed without diagnosis. You can also compare ventilation approaches in MVHR vs PIV: Which Home Ventilation System Is Best for Your House?.
Reusable airflow test sheet
Copy the following fields into a notebook or spreadsheet:
- Date, address and tester
- System type and fan model, if known
- Room and terminal location
- Terminal type and approximate size
- Operating mode: normal, boost or other
- Windows and doors: open or closed
- Instrument, serial number and calibration status, if applicable
- Reading, units and number of repeat readings
- Visual condition, noise, vibration and observations
- Action required and date of retest
What to double-check
Use the right reference. A reading should be compared with the system design, installation specification, manufacturer’s instructions and applicable Building Regulations guidance for the project. Requirements can depend on the dwelling, system type, room use and whether the work is a new installation, replacement or alteration. Do not present a general online airflow table as proof of compliance.
Check the instrument’s limitations. An anemometer measures air velocity at a point; it does not automatically provide volume flow. A capture hood can be more suitable at a grille, but it still needs correct positioning and appropriate range. Very low flows, turbulence, compact grilles and nearby bends can reduce reliability.
Look for the cause of a low reading. Check filters, grilles, fan settings, duct restrictions, external terminals, transfer paths and power supply before replacing a fan. If several terminals are low, investigate the central unit or duct system. If only one is low, inspect that branch and grille first.
Keep compliance evidence separate from fault-finding notes. For a property handover, renovation or formal commissioning record, include equipment details, method, operating mode, terminal readings and any adjustments. A photograph of a tissue being held near a grille may demonstrate direction, but it is not a commissioning certificate.
Common mistakes
- Testing only one room: ventilation is a connected system. A working bathroom fan does not prove that the kitchen, bedrooms or supply terminals are adequately served.
- Testing with doors and windows in an unusual position: record the test conditions and repeat them consistently.
- Ignoring replacement air: extraction needs a path for air to enter. A fan may become noisy or ineffective when a room is tightly closed.
- Measuring a grille incorrectly: do not partially cover a terminal or press a probe into it. Follow the instrument guidance.
- Changing settings before recording them: note the original speed, boost and timer settings so the system can be restored if needed.
- Assuming more airflow is always better: excessive airflow can cause draughts, noise and unnecessary heat loss. The target is suitable, controlled ventilation.
- Cleaning without checking the root cause: mould and window condensation can involve moisture production, cold surfaces, insulation or building defects as well as ventilation.
If you need a broader maintenance plan, use the guidance in How to Stop Condensation and Mould in Your Home alongside the airflow record.
When to revisit
Repeat a basic visual and functional check at sensible seasonal intervals, particularly before colder weather when windows are closed more often and condensation becomes easier to notice. Recheck after cleaning a filter or grille, replacing a fan, altering ductwork, insulating or refurbishing a room, or changing an MVHR or PIV control setting.
Arrange measured testing when a new system is installed, after significant remedial work, during a property handover, or when persistent condensation, mould, odour, noise or draughts remain. Keep the previous test sheet so that changes in airflow can be identified rather than guessed.
Practical next step: walk through the property with the checklist, photograph each terminal, record the system settings and mark any blocked, noisy or inaccessible component. Clean only what the manufacturer permits, then repeat the same checks. If the result is being used to demonstrate compliance or the system cannot be balanced, use a qualified ventilation professional with appropriate calibrated equipment and request a written report.
