Acoustics -

The properties or qualities of a room, space or building that determine how sound is transmitted in it. Acoustics can play a critical part in how loud or quiet the perceivable volume of a fan installation can be. For more information click here.

Visit our Noise Levels Explained article.

Aico -

Aico, an Ei Company, are the European Market Leader in Home Life Safety. All Aico alarms meet UK standards and offer a variety of sensor types to guarantee protection for every home, the cornerstone of which is delivering education, quality, service and innovation. Contact: 01691 664100.
View our range of Aico Products.

Air Changes per Hour (ACH) -

Air changes in relation to the volume of a room. Usually measured in m3/h (Metres cubed per hour) or l/s (litres per second).

Air Exchange Rate -

The number of times air in a space is replaced with fresh air within a given time period.See also Extraction Rate, Airflow Rate.

Air Purification -

The process of removing contaminants such as dust, pollen or other pollutants from the air to improve indoor air quality.
View our range of Air Purifiers.

Airflow -

Airflow developments have a rich history of innovation and growth and to this day have made many products that are unique and efficient. In 1955, from one man's expertise in the fields of fan design and air flow measurement, the Airflow Developments group of companies was founded. Initially based in one factory in High Wycombe the company has since blossomed into a thriving international group. With the search for new opportunities, the Company's ongoing expansion was strengthened by opening subsidiaries in Germany and the Czech Republic, supported by a worldwide sales distribution network. Contact: 01494 525252.
View our range of Airflow Products.

Airflow -

The movement of air in a specific direction.

Airflow Rates -

Measurement of a flow of air through a ventilation unit or duct.
See also Extraction Rate.

Axial Fans -

Most common style of Bathroom wall mounted fan. Specific design of fan impeller or blades used to move air where the air flows parallel to the axis of rotation. Most domestic wall fans are axial. Axial fans are great for small duct runs of less than 5m. They usually come in different versions, being operated, for example by a timer, humidistat, pull cord or PIR and may be switched on by the lights. Some axial fans are available in both 240v and SELV 12v for when installing in Zones 1 and 2 of the bathroom. Axial fans are not good for long duct runs. Anything over 5m will impair their ability to extract air because of the larger air pressures present in the duct.
View our range of Axial Bathroom Fans.

Back Draft -

Air that flows backwards into a property through ducting when the extraction unit is dorment.

Back Draught Shutter -

A back draught shutter can take a couple of forms but performs the same function: They prevent air travelling back up the duct, through the impellars of the fan and into the room - particularly important in winter! Back draught shutters may be integral to the fan, in which case they may be as simple as a one way hinged membrane (they blow backwards when the fan is on, but cannot bend forward when it's off), or may be thermo-electrically controlled. However, back draught shutters are also available as stand alone units which may be fitted anywhere in the duct run. These are more commonly used when one is fitting a centrifugal fan.

Bathroom Fan -

An extractor fan designed specifically for removing moisture and odours from bathrooms.
View our range of Bathroom Fans.

Bathroom Zone -

Bathrooms and the increasingly popular wetrooms are divided into different areas, or zones, which allow an installer to work out the likelihood of water exposure and therefore pick the correct product to install in the correct area that adheres to the safety regulations. Bathrooms have three zones for bathtubs and shower trays, whereas wetrooms have just two zones. The higher the zone number the lower the risk of water exposure - for example Zone 0 is a high risk area whereas Zone 2 is a relatively low risk area. Each zone has a specific three dimensional volume and anything within the “box” created is rated as within the zone.
Visit our Guide to Bathroom Zones.

Boost Speed -

This term is used specifically in relation to continuous ventilation units which offer a low continuous extraction rate, (referred to as Trickle) and higher 'Boost' extraction rate for times when increased airflow is required - for example when the shower is in use.
View our range of Ventilations Systems.

Building Regulations -

A minimum standard for design, construction and alteration of buildings. Part F of the Building Regulations specifically covers ventilation requirements where part 1 looks specifically at ventilation requirements for dwellings.
Visit our Guide to Building Regulations.

Centrifugal Fan -

Centrifugal fans blow air at right angles to the intake of the fan, and spin the air outwards to the outlet (by deflection and centrifugal force). The impeller rotates, causing air to enter the fan near the shaft and move perpendicularly from the shaft to the opening in the scroll-shaped fan casing. A centrifugal fan produces more pressure for a given air volume, and is used when longer duct runs are necessary. Centrifugal fans can be an Inline duct fan or a wall mounted fan.
View our range of Centrifugal Fans.

Condensation -

The process by which water vapour in the air becomes liquid as it cools.

Condensation Trap -

A collar installed within a verticle duct run to allow for the collection and removal of condensation from a venting system. Used predominently on verticle venting through roofs but an important addition to any verticle ducting that is higher than the fan unit's location.
Visit our Guide to Condensation Traps. 

Constant Live -

A positive side of an electrical circuit with continuous current.

Continuous Ventilation -

Increasingly popular, this term is applied to ventilation devices which run 24 hours a day at a low 'Trickle Rate' and can be boosted to higher extyraction rates when needed. See also dMEV, MEV, Heat recovery and MVHR.
Visit our Guide to Extractor Fan Wiring.

Damp -

A problem where moisture build-up or moisture ingress into a building or structure can cause both damage to the fabric of the building and/or promote mould from forming.
Visit our Guide on How to Prevent Mould and Condensation.

dB (Decibels) -

Decibels are a measurement of sound which can be confusing. The linear rise in decibels does not correlate to the logarithmic curve that tracks the perceived volume we hear as humans. Effectively, the best way to describe how we perceive sound is that the perceived volume we hear doubles every 10dB.
For more information visit our Noise Levels Explained article.

Demista -

Demista Pads are supplied by Heat Mat. Heat Mat is one of the leading manufacturers and distributors of electric underfloor heating in the UK and the brand name of choice for the professional installer. Contact: 01444 247020.
View our range of Demista Products.

Diffuser Grille -

An internal grille designed to allow the user to control the airflow either into or out of a room by adjusting a valve that can be spun open to allow higher air flow to pass or spun closed to limit or stop airflow altogether. Used predominantly with multi-room systems such as MEV or MVHR systems. Not normally suitable for use with inline fans.

dMEV - Decentralised Mechanical Extract Ventilation -

dMev is the term given to a single room MEV unit. The distinguishing feature between a dMEV unit and normal extractor fan is the fact that a dMEV unit is continuous running. They constantly extract air from a room at what is known as a 'Trickle Rate'. Most dMEV units also feature a 'Boost' flow rate which is comparable to the extraction offered by a standard extractor fan for times of increased demand - such as shower time when more steam is present.
Visit our Guide to dMEV Fans.

Domus -

Domus Ventilation is a manufacturer of market-leading ventilation systems that save energy and improve indoor air quality. Established over 30 years ago, and now part of the Genuit Group, Domus Ventilation manufactures high quality and solution based ventilation products for the domestic and light commercial building industry from its state-of-the-art production facilities in South Wales. The company provides differentiated ventilation solutions, transforming the way developers, contractors, installers, home owners and distributors meet Building Regulations Parts F & L and emerging environmental standards. Previously Silavent. Contact: 03443 715523.
View our range of Domus Products.

Duct -

Duct or ducting is the pipe which takes the extracted air away from the extraction zone. It comes in various sizes to match the spigot sizes of extractor fans. The most common domestic sizes are 4 and 6 inch, but commercial fans will use 9 and 12 inch ducting. The most common types of ducting are solid, pvc, aluminium and insulated. The general rule is that you can only use ducting that has an equal or larger diameter than the fan unit but never ducting with a smaller diameter than the fan unit. This is to reduce putting any pressure on the fan motor by constricting the airflow.

Envirovent -

EnviroVent is one of the UK’s leading manufacturers of low energy, sustainable domestic ventilation equipment designed to create all year round, healthy fresh and ideal indoor environments. Contact: 01423 810810.
View our range of Envirovent Products.

Exhaust Fan -

Different terminology for extractor fan.

External Louvre -

A vent cover designed to prevent the entry of rain, debris, and pests into ventilation openings.
See also Gravity Grille.

Extraction Rate -

Extraction rate is the term given to the amount of air extracted over a given period. This figure is commonly represented in one of two ways: Either as metres cubed per hour (m3/hr) or litres per second (L/s). A half decent extractor fan should be somewhere around 70m3/hr or 20L/s. To convert m3/hr into L/s simply multiply the L/s figure by 3.6 so 25L/s = 90m3/hr.

Extractor Fan -

A unit designed to expel air from an enclosed space.

FAI (Fresh Air intake) -

Passive vent or opening that allows outdoor air to return into an enclosed space.
See also Trickle Vent.

Fan Speed Controller -

A device used to adjust the speed of a fan and therefore control airflow speed.

Filter -

Used in some units to filter particle matter from the air. More commonly found in whole house ventilation systems and some kitchen fan units.
See also Grease Filter.

Filtration -

The process of removing particles and contaminants from the air using filters.
View our range of Air Purifiers.

Forced Ventilation -

The use of fans or mechanical systems to actively circulate air and provide ventilation.
See also Positive Pressure Ventilation.

Free Air -

The movement of air through an unobstructed route.

Gravity Grille -

A passive external vent cover designed with hinged louvres that fall closed when not in use to minimise backdrafts and are blown open by the escaping air when the extractor fan is in operation.

Grease Filter -

A filter designed to capture and remove grease particles from the air, commonly used in kitchen ventilation.

Greenwood -

Greenwood was founded in 1879 and today is a market leader in the design, manufacture and specification of SMART ventilation systems for new build and refurbishment residential markets.
View our range of Greenwood Products.

Grille -

The Grille finishes off the installation. Internal and external grilles prevent objects entering the duct run.

Heat Exchange Unit -

A device manufactured from thermo-conductive materials used in heat recovery systems such as MVHR units.
View our range of Single Room MVHR Units.

Heat Mat -

Heat Mat is one of the leading manufacturers and distributors of electric underfloor heating in the UK and the brand name of choice for professional installer. Contact: 01444 247020.
See also Demista.

Heat Recovery -

The practice of transfering the heat from old / stale / moist air which is being extracted from a room or building to the fresh incoming air going back in to the building via a heat exchanger. Heat Recovery can lower heating bills whilst improving air quality.

Heatmiser -

Heatmiser UK is located in Blackburn, in the heart of Lancashire. Established in 1968, Heatmiser has become one of the UK’s leading smart room thermostat manufacturers. Heatmiser has established partnerships with heating installers and heating equipment manufactures across the UK and has the ability to private label and custom design. Contact: 01254 669090.
View our range of Heatmiser Products.

HEPA Filter -

High-Efficiency Particulate Air filter that captures fine particles and allergens in the air.
View our range of Air Purifiers.

Humidistat -

A humidistat measures the relative humidity of the air. If the RH reaches a pre-set level the humidistat will turn the fan on. Humidistats may be integral to the fan, (in which case the fan code usually includes an 'H' such as QT100HT or ST100HT) or may be separate switch units. In the latter case, remote humidistats are used to switch inline duct fans, which of course do not sit in the room from which they are extracting air.
Visit our Guide to Setting Up Humidistat Fans.

Humidity -

Amount of moisture in the air. Usually measured by percentage - for example 70% humidity.

HVAC (Heating, Ventilation, and Air Conditioning) -

The system responsible for regulating indoor climate and air quality.

Impeller -

The impeller in a fan is the blade assembly. Impellers come in two main types: axial or centrifugal. The more common for domestic fans is axial as these are cheaper to produce and require smaller housing. Impellers may be backward or forward curved and may have any number of blades. Axial impellers commonly have between 8 and 11 blades and pull air through them linearly. Centrifugal impellars blow air at right angles to the intake of the fan, and spin the air outwards to the outlet by deflection and centrifugal force.

Indoor Air Quality (IAQ) -

The cleanliness and healthiness of the air inside a building, which can be improved through ventilation.
View our range of Air Purifiers.

Inline Fan -

Inline fans, as the name suggests are situated in the length of ducting. They therefore look completely different from wall fans but most importantly are not installed in the room from which they are extracting air. Ducting will run from one end of the fan to a ceiling grille in the extraction zone and from the exhaust end of the fan to the outside grille. Inline fans are excellent for use above bathrooms or kitchens where extra extraction power is required. Inline fans almost always use a centrifugal impeller and as such can usually extract over very long duct runs.
View our range of Inline Fans.

Intermittent Ventilation -

Mechanical ventilation that does not run all the time, usually running only when there is a particular need such as cooking or bathing/showering. Intermittent fans can be controlled either manually or automatically.

Joist -

Horizontal structural beams in a building's framework, which can affect the layout of ventilation systems.

Kilowatt (kW) -

A unit of power often used to quantify the energy consumption of fans and other ventilation equipment.

Kinetic / Kinetic Switching -

Kinetic is the energy of movement. Some wireless switching systems utilise kinetic energy to create a small electrical charge by converting movement energy into electricity. This is used to produce a radio signal that can be received to trigger fans and other electrical appliances into operation.
See the Culina Konect switching options for more information.

Kitchen Extraction -

The process of removing airborne grease, smoke, and odours from cooking spaces. Most kitchen fans are 150mm or 6" axial fans and will extract a minimum of 60l/s in line with the extraction rates stated in Part F of the Building Regulations.
View our range of Kitchen Fans.

Kitchen Hood -

A canopy or enclosure positioned above a cooking area to capture and remove cooking-related pollutants. These usually pull air through a filter and will either extract the air out of the building or recirculate the air internally once filtered. These are specialist units with fan motors designed to pull aitr passed a filter rather than extractor fans that pull free air only.

Knockout -

A perforated section on a duct or ventilation component that can be removed to create an opening for connections.

L/S (Litres per Second) -

A measurement of air movement.See also m3/h (metres cubed per hour).

Lint Trap -

A filter or screen used to capture lint and debris from exhaust air, commonly used in dryer vents. Not suitable for household extraction units as these collect dust and lint which over time build up to restrict the airflow.

Live -

The positive side of an electrical circuit.
Visit our Guide to Extractor Fan Wiring.

Louvre -

A slatted opening or panel that allows airflow while preventing the direct entry of rain, debris, or animals. Can also block direct line of sight through vent openings.

Manrose -

Formed in 1987, UK-based manufacturer Manrose is a leading manufacturer of domestic ventilation fans and equipment. Manrose offers mechanical extract ventilation fans, heat recovery products, hand dryers, electrical heating systems and cooling products. Manrose also provides accessories such as electrical controllers, electrical speed controllers, roof vent kits, ducting and ventilation accessories and boxed venting kits.Our products are used in various domestic and commercial applications. Contact: 01753 691399.
View our range of Manrose Products.

Mechanical Ventilation -

Powered devices to actively move air and provide ventilation.

MEV - Mechanical Extract Ventilation -

MEV is the term given to a special type of ventilation unit which extracts air from the whole house. Situated centrally in the loft or sometimes cupboard, MEV units has multiple duct connections which are receive stale air from multiple rooms. It then expels the waste air through one duct run to the outside world.
View our range of MEV Units.

Mixed Flow Fans -

Mixed Flow Fans combine the characteristics of both axial fans and centrifugal fans. The air moves in both an axial and radial direction relative to the shaft. Mixed flow fans, like centrifugal fans, develop higher pressures than axial fans. Since this technology is only ever used in Inline Fans, the terms are interchangeable.

Monsoon -

See National Ventilation.
View our range of Monsoon Products.

Mould -

A type of fungus that thrives in damp areas. Mould can be both hazardous to health and cause damage to building structure.
Visit our guide to the best fan options for Combatting Mould and Condensation.

MVHR - Mechanical Ventilation Heat Recovery -

MVHR is the specific term given to a special type of ventilation system that not only extracts stale air form a room or whole house, but also returns fresh air from outside that has been warmed by the extracted air through a heat exchanger. MVHR systems are becoming a very popular method of ventilation as it both keeps air fresh and saves heating costs.
View our range of Whole House Heat Recovery Systems.

National Ventilation -

National Ventilation is a leading supplier of innovative, energy efficient, low noise ventilation products across the domestic, commercial and industrial sectors, all designed to improve air quality. In the last year alone National Ventilation has seen huge growth and continued to build and support our enviable reputation for great service. 
National Ventilation is a leading supplier of innovative, energy efficient, low noise ventilation products across the domestic, commercial and industrial sectors, all designed to improve air quality. In the last year alone National Ventilation has seen huge growth and continued to build and support our enviable reputation for great service. The National Ventilation team are all dedicated to help with all your ventilation needs, this includes a network of Area Sales Engineers and Special Projects Team which cover the whole of UK, and this is backed up by a Technical Sales Team based in Somerset. Working through approved wholesalers and ventilation stockists, we provide a full design service, site visits, consultations, quotations and technical support, all free of charge. Manufacturers and suppliers of Monsoon Products. Contact: 01823 690290.
View our range of Monsoon Products.

Natural Ventilation -

The process of allowing fresh air to passively ventilate such as open windows or passive trickle vents.

Negative Pressure -

A condition where indoor air pressure is lower than outdoor air pressure, causing air to be drawn into the building. On a smaller scale, negative air pressure can be created in a single room such as a bathroom by extracting moisture laden air, causing fresh dry air to be pulled into the room from the rest of the house and minimising the amount of moisture laden air from flowing into the house from the bathroom area.

Net Free Area -

The unobstructed opening in a vent or grille that allows air to pass through.

Nine Inch Extractor Fan -

A nine inch extractor fan is a very powerful fan usually used in commercial installations including larger kitchens, restaurants, club rooms, pubs, shops and offices.

Noise Control -

Techniques used to minimize noise generated by ventilation equipment, ensuring quieter indoor environments.

Noise Rating or NR -

A measurement of noise, usually measured in dB (decibels). For more information click here.
Visit our Noise Levels Explained article.

Odour Control -

Methods and technologies employed to remove or neutralise unpleasant odours from the air.
See an example from Vent Axia.

Outlet -

An opening through which air can exit.

Outside Air -

Fresh air from the outdoors that is introduced into a building's ventilation system for improved indoor air quality.

Over Run Timer -

A device usually integral to the fan which permits operation after the fan has been manually turned off. Usually adjustable from around 3 - 30 minutes the over run period is determined during installation. This functionality ensures moisture extraction continues after the room is vacated and the source of the moisture (usually a shower) has been turned off.
See also Timer.

Overpressure -

A condition where indoor air pressure is higher than outdoor air pressure, causing air to be pushed out of the building.
See also Positive Pressure

Part F - Building Regulations -

Part F of the Building Regulations specifically covers ventilation requirements where part 1 looks specifically at ventilation requirements for dwellings.
Visit our Guide to Building Regulations.

Particulate Matter -

Tiny particles suspended in the air that can be harmful to health, which can be removed by filtration in certain ventilation systems.
View our range of Air Purifiers.

Passive Grille/Passive Ventilation -

Non mechanical vent that allows air to move through it naturally.See also Trickle Vent.

PIV (Positive Input Ventilation) -

A ventilation system that pushes air into a property to reduce humidity and contaminants rather than extracting air. Positive Input Ventilation or PIV systems have been around for decades and largely only used to treat condensation and mould issues. However in recent times, PIV has seen a resurgence in both domestic and commercial settings as the need for clean, fresh air has become more important than ever.
See also Positive Pressure Ventilation.
Visit our Guide to PIV Systems.

Plenum -

Plenums or Plenum boxes are junctions used to facilitate the pulling in, distribution and extraction of airflow in a multi vent extraction systems such as MEV and MVHR systems.

Positive Pressure Ventilation -

A ventilation system that pushes air into a property to reduce humidity and contaminants rather than extracting air. Also known as Positive Input Ventilation or PIV, these systems have been around for decades and largely only used to treat condensation and mould issues. However in recent times, PIV has seen a resurgence in both domestic and commercial settings as the need for clean, fresh air has become more important than ever.
Visit our Guide to PIV Systems.

Pressure Drop -

The decrease in air pressure as it flows through a ventilation system, often due to friction and resistance.

Pullcord -

A pullcord is a cord attached to an extractor fan, which turns the fan on and off. Not so common nowadays on Bathroom Fans, but still popular on Kitchen Fans.Some pullcords are used to activate secondary functions such as delayed starts as well as a manual on/off function such as the Tornado ST100HT

Purge Ventilation -

Facility to change air within a room at a rapid rate (i.e. open a window). Some fan units have a purge function that periodically either turns on an intermittant fan to purge a room or boosts a continuous flow fan for the same effect. 
See the Room Refresh mode on the Airflow QT100T as an example of this.

Quality of Air -

The cleanliness and healthiness of the air within a property or the cleanliness and healthiness of the air provided by a ventilation system, influencing indoor air quality.

Quantity of Air-

The volume of air moved through a ventilation system within a given time, often measured in m3/h or l/s.

Radon -

A harmful gas formed underground in rock which can seep up naturally into buildings.

Recirculation Mode -

An operation mode where a ventilation system recirculates indoor air without bringing in fresh outdoor air. Most notibly found as the functionality of many kitchen extractor hoods or cooker hoods where the air is pulled through a filter and reintroduced into the room.

Resistance -

Friction caused by accesories and components used in ventilation such as ducting, grilles, backdraft shutters etc.

Return Air -

The air that is pulled back into a ventilation system to be conditioned and recirculated.

Roof Vent -

A vent installed on the roof of a building to allow for the escape of stale air and moisture.
See also Tile Vent. 
For more information on venting vertically through roofs visit Our Guide.

Silavent -

See Domus.
View our range of Silavent Products.

Soffit Vent -

A vent installed in the eaves or soffits of a building to facilitate air intake or exhaust.
Ideal grille type for this use are the fixed external grilles.

Spigot -

A spigot is the connecting section found on fans, grilles and other ducting items which fits tightly into the ducting for the transference of air through the system. When using solid ducting, a fan or grille spigot will fit snugly into the duct, however if flexible ducting is being used, a duct clamp will be needed to affix the ducting onto the spigot to hold in place firmly.

Static Pressure -

The resistance that air encounters as it moves through ducts and components in a ventilation system.

Switch Live / Switched Live -

A live line that is controlled by a switch or sensor - most commonly the light switch which will activate the fan at the same time the lights are turned on.Visit our Guide to Extractor Fan Wiring.

Timer -

A device usually integral to the fan which permits operation after the fan has been manually turned off. Usually adjustable from around 3 - 30 minutes the over run period is determined during installation. This functionality ensures moisture extraction continues after the room is vacated and the source of the moisture (usually a shower) has been turned off.See also Over Run Timer. 

Tornado -

Tornado Ventilation offer high end extraction at an affordable price. With both the Silent Tornado axial fans and the Turbo Tube inline fans, our ranges offer high extraction rates, low running noise and confidence in the quality of our products with a 5 year warranty as standard across all units. In 2022 the range underwent an overhaul which saw fresh new designs and upgraded components across the ranges. This included an upgraded bearing set and more efficient motors across the ranges; a more attractive, slimline front grille for the Silent Tornado range and a more user friendly casing for the Turbo Tube range. With over a decade of experience, Tornado Ventilation are proud to offer high end ventilation solutions you can rely on.
View our range of Tornado Products.

Total Equivalent Length (TEL) -

The combined length of ducts, fittings, and other components that contribute to airflow resistance.

Trickle Speed / Trickle Flow -

Low continuous extraction rate used in continuous fan units such as dMEV, MEV Heat Recovery and MVHR systems.
See also Boost Speed.
View our range of Ventilation Systems.

Trickle Vents -

Passive ventilation - normally fitted in windows or as air bricks in walls.

Velocity -

Speed at which air travels through a duct or ventilation unit.

Vent Axia -

For 80 years, Vent-Axia has set the ventilation standard. Founded in 1936 by Joe Akester, we are immensely proud of our heritage as a dynamic British manufacturer. From the World’s first electrically-operated window fan, to the first App controlled bathroom fan, we have always been forward-thinking, innovative and dedicated. Contact: 08448 560 580.
View our range of Vent Axia Products.

Ventilation -

Removal of moist and/or stale air and/or the introduction of fresh air to a dwelling.

Ventilation Duct -

A tube used to transport air from one area to another within a ventilation system, which can be solid/rigid, semi-rigid or flexible. Solid ducting is the most effective for maximising airflow and minimising noise and is available in round of flat options, whereas flexible ducting is the easier option for difficult installation paths.

Venturi Effect -

The reduction in air pressure that occurs when air flows through a constricted section of a duct or component.

VOC -

Volatile Organic compounds - colourless and odourless gas released from various household products.

Whole House Ventilation -

The continual ventilation rate within a dwelling. More often associated with multi-vent systems such as MEV and MVHR.
View our range of Whole House Ventilation Systems.

Wireless -

Radio controlled operation of boost or fan speed.See also Kinetic Switching.

Y-Piece -

A duct component that divides airflow into two branches, often used to connect multiple ventilation lines.

Year-Round Ventilation -

Ventilation systems designed to operate effectively in all seasons, maintaining comfortable indoor conditions.

Zoning -

Dividing a building into different zones for independent control of ventilation and temperature, most often utilised in smart homes for extraction programming.
See also Bathroom Zones.