Ventilation Glossary

Air change rate: How many times an hour the air in a space is replaced, often written ACH.
Air handling unit (AHU): Central plant that filters and moves air, and often heats, cools or recovers heat, for a building.
Airtightness: How little air leaks through the fabric of a building, measured in an air test.
Approved Document F: Government guidance on meeting the ventilation requirements of the Building Regulations in England.
Awaab's Law: Rules requiring social landlords in England to investigate and fix certain hazards, including significant damp and mould, within set timescales.
Background ventilator: A small, controllable opening such as a trickle vent that lets outside air in.
Boost: A higher fan speed used for showers or cooking.
BS 6173: The British Standard covering gas appliances in commercial catering, including interlocks with ventilation.
Canopy: The hood over a commercial cooking line that captures heat and grease.
Capture velocity: The air speed needed at a source to draw contaminants into an LEV hood.
CO2 monitoring: Measuring carbon dioxide to judge whether a room gets enough fresh air for its occupants.
Commissioning: Measuring and setting a ventilation system's airflows and recording the results.
Condensate drain: A pipe that carries away water condensed inside a heat recovery unit.
Condensation: Water that forms when moist air touches a surface colder than its dew point.
COSHH: The Control of Substances Hazardous to Health Regulations, which cover LEV maintenance and testing.
dMEV: Decentralised mechanical extract ventilation: continuous low-energy fans in each wet room.
Dew point: The temperature at which moisture in the air starts to condense.
Diffuser: A ceiling or wall terminal that spreads supply air into a room.
Ductwork: The pipes and fittings that carry air between fans and rooms.
EC fan: An electronically commutated fan: efficient, speed-controllable and direct-drive.
Extract rate: The airflow a fan removes, usually in litres a second.
Flow hood: A calibrated instrument placed over a fan or valve to measure airflow.
Gas interlock: A control that stops gas to cooking appliances unless ventilation is running.
Grease filter: A baffle or mesh filter in a canopy that catches grease.
Heat exchanger: The core of a heat recovery unit where outgoing air warms incoming air without mixing.
HHSRS: The Housing Health and Safety Rating System used in England to assess hazards such as damp and mould.
HSG258: HSE guidance on controlling airborne contaminants with LEV.
Humidistat: A sensor that switches a fan on when humidity rises.
Inline fan: A fan fitted in the duct, often in the loft, rather than at the grille.
LEV: Local exhaust ventilation: extraction that captures contaminants at source.
Litres per second (l/s): The usual unit for ventilation airflow in the UK.
Make-up air: Fresh air supplied to replace air extracted from a kitchen or space.
MEV: Mechanical extract ventilation: one central fan extracting from all wet rooms continuously.
MVHR: Mechanical ventilation with heat recovery: whole-home supply and extract through a heat exchanger.
PIV: Positive input ventilation: a unit that gently pushes filtered air into the home.
Plenum: A box or chamber that connects a fan or canopy to the ductwork.
Relative humidity: How much moisture the air holds compared with the maximum at that temperature.
Rotary heat exchanger: A rotating wheel that transfers heat (and some moisture) between air streams.
SFG20: The standard library of building maintenance schedules widely used for planned maintenance.
Summer bypass: An MVHR feature that lets fresh air skip the heat exchanger in warm weather.
TR19: BESA's specification for cleaning ventilation (TR19 Air) and kitchen extract (TR19 Grease) systems.
Trickle vent: A small background ventilator, usually in a window frame.

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