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A Beginners Guide To Ventilation

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By Ruth MacEachern

Product Manager

Mar 06, 2020

An effective ventilation system is an essential part of any home or business premises. Ventilation refers to any system that allows air to flow and move between the inside and outside of a property, providing fresh air for the occupants. 

In the past, buildings relied on natural or uncontrolled ventilation. It could involve opening windows and doors, fixed air vents, and natural gaps in the structure. It is not always effective in a modern property - though, especially as energy-efficient homes and offices are built to increasingly airtight designs. Natural ventilation can either over ventilate or under ventilate a building and is uncontrollable. 

Mechanical systems are often required to achieve the required airflow rates in a building. These can help safeguard the health of the occupants and prevent issues such as damp. For new-builds, it might also be a building regulations requirement, while some workplaces will have ventilation as part of their health and safety requirements. 

Adequate ventilation is essential in maintaining a healthy environment, as it: 

  • prevents the build-up of excess levels of humidity (which can lead to condensation, mould and can consequently result to health issues) 
  • provides air for fuel-burning appliances, such as wood burners 
  • removes cooking smells 
  • in some instances it can help remove allergens and other irritants, such as tobacco smoke. 

The core ventilation methods are: 

Mechanical Ventilation with Heat Recovery 

Positive Input Ventilation 

Continuous Mechanical Extract Ventilation 

Natural Ventilation with Intermittent Extract Fans and Background Ventilators.

Buildings are ventilated through a combination of uncontrolled ventilation (draughts, air bricks and trickle vents, etc) and, increasingly in new homes, controlled ventilation solutions such as mechanical ventilation with heat recovery. 


Mechanical Ventilation with Heat Recovery (MVHR) is a whole house ventilation system that both supplies and extracts air throughout a property. Heat recovery is a domestic heat recovery system, which is increasingly used to reduce the heating and cooling demands of buildings. Heat recovery systems typically recover about 73–95% of the heat in exhaust air and have significantly improved the energy efficiency of buildings.

MVHR is an ideal choice when: 

✔ You are doing a full renovation or building a new house rather than a retrofit. 

✔ You require a whole house ventilation solution. 

✔ You want to make your home energy efficient. 

Some newer builds are aiming for a low air permeability requires controlled ventilation to be able to balance airflows effectively, has a more measured take on ventilating dwellings, and also provides both the installer and homeowner to have a more personalised level of controllability over their indoor air quality. As the airtightness therefore improves, so does the requirement for controlled ventilation – most commonly in the form of MVHR – in order to maintain a healthy environment without the needless loss of too much heat. 

MVHR systems consist of two independent ducted airflows, each with its own fan: 

The extract fan extracts the stale, humid air from the wet rooms (bathrooms, kitchen, utility, etc). This stale air is then passed over a heat exchanger – where heat is ‘recovered’ – before it is discharged outside the house. The second fan draws fresh air from outside. It then filters it to get rid of pollution and airborne allergens, and then passes it over the heat exchanger in order to warm it — and so supplies pre-warmed fresh air to all the living areas and bedrooms. 

Besides the drive to make houses more efficient, there are other reasons, which lead towards the installation of MVHR systems: 

Noise: if there are noise complaints with a dwelling, e.g. traffic or airport, MVHR systems with adequate silencers will provide a good solution for ventilation without the need to open windows. Additionally, noise reduced glazing will help. 
Air quality: if the air quality is problematic, e.g. for people suffering from hay fever, various kind of filtration in MVHR systems can deal with pollen, rural and industrial smells. Also, the position of the air intake can be carefully chosen in order to avoid the intake of polluted air from nearby roads. 
High levels of humidity: Besides constant ventilation, MVHR systems will actively dehumidify when it is outside colder than inside. 
Comfort: In areas with high midge infestation, MVHR systems with good tight-fitting filters can help to keep the dwelling free from these flying insects. 

MVHR units are fairly sizeable products, as the air needs space to move efficiently and quietly. A good insulated housing will also add to the size of the MVHR unit. 

Things to consider for situating an MVHR unit: 

Easy access for filter changes and maintenance. For accessing your MVHR unit, you probably don’t want to balance over a stretch of ceiling joists, whilst trying not to stick your foot through the ceiling. 

Maintenance space around the MVHR unit (typically 500mm in front of the unit). 
Ideally the unit is situated in a central location, which minimises duct runs.

Often the unit is placed within the thermal envelope, e.g. a utility room, plant room, warm loft or store room. In this case the unit should be close to an external wall, which keeps the intake and exhaust ducts as short as possible.

Well insulated units can also be installed outside the thermal envelope, e.g. in a garage: In such cases situate the unit close to the partition wall of the house, in order to keep the supply and extract ducting as short as possible.

Smaller MVHR units can also be ceiling mounted with a maintenance hatch. In this case the unit should be close to the external wall with the intake and exhaust penetrations.

If all this is not possible, MVHR units can be installed in a cold loft. In this case particular attention needs to be paid that the supply and extract ducting, which carry ambient air, are not exposed to the cold. Ideally these are placed fully underneath the loft insulation. If this is not possible for some lengths of ducting, these need to be insulated well. The UK standard is 25 mm of quilt insulation (or equivalent), but we find that it should rather be 50mm to 100mm of quilt insulation with aluminium foil coating. This needs to achieve a set thermal conductivity rate, so this should be checked.

A MVHR unit can make your home more energy efficient when installed correctly, extracting moisture caused by condensation which can be especially prevalent in wet rooms like bathrooms and kitchens. All of our MVHR products offer a wide range of innovative benefits in addition to exceptional performance and low maintenance. 


Positive Input Ventilation (PIV) works as a whole house ventilation system and creates healthy living environments by supplying fresh, filtered air into a property at a continuous rate throughout the dwelling. This is a very popular method of whole house ventilation.  

PIV is required when: 

✔ You don't want to do a full renovation. 

✔ You require a whole house ventilation solution. 

✔ You don't want to remove any walls or go back to brickwork.

Positive Input Ventilation (PIV) is a whole house air ventilation system that works by drawing in fresh, filtered air into a property from outside. These can be either installed in a loft space or on a wall in a flat or apartment. They ensure that a continuous supply of air is supplied into the home to eliminate or significantly reduce condensation.  


The central unit draws air from either the loft or outside, filters it, and delivers it into the property, creating a positive pressure which, in turn, forces the stale air out. 

New airtight homes are recommended to install a heat recovery ventilation system (MVHR) or a continuous mechanical extract system (MEV/d-MEV) and ideally not a positive ventilation unit (PIV). A positive ventilation unit works by pressurising the property and the contaminated air is pushed out through natural paths in the dwelling's facade or window trickle vents. If the property is built at or below 3 m3/hr/m2 air losses at a pressure of 50 Pa there would not be enough air leakage for the unit to work effectively, and background ventilation methods such as trickle vents in windows.

MEV (or d-MEV) 

Continuous mechanical extract ventilation (MEV or d-MEV) is almost the opposite of PIV and is effectively either a centrally situated fan or independent set of fans that gently extracts stale or moist air from points of high humidity such as the bathroom or kitchen. 

This creates a negative pressure, which theoretically draws fresh air evenly into the property through the envelope of the building. 

MEV d-MEV is required when: 

✔ You are doing a full renovation or building a new house.

✔ De-centralised MEV or d-MEV is also a great option if retrofitting.

✔ You want an easy to install, whole house ventilation solution. 

✔ You want a fit and forget solution. 

Continuous Mechanical Extract Ventilation (MEV) refers to centralised and de-centralised systems which provide extract ventilation helping to reduce excess moisture using either a multi point extract or singular fan. MEV systems provide all year round good indoor air quality, protecting your home from condensation, damp and mould. Our MEV systems also come with a 2-year guarantee, giving you peace of mind when purchasing.  

Extractor Fans 

Extractor fans are a functional and practical solution for controlling excess humidity, smoke, heat removal or unwanted odours. Bathroom extractor fans are generally smaller than kitchen extractor fans but can come with a timer for more efficient use. 

A bathroom is a wet room by definition, so providing proper ventilation is imperative, both for the occupant's health and for the bathroom itself. Renewing the ambient air limits the emergence of any condensation and the appearance of mould all the while reducing the humidity level. 

Bathrooms and wet rooms are divided into zones, based on proximity to water sources. An industry standard, the IP rating, designates the zones in which any electrical fixtures or equipment can be installed. There are special requirements for extractor fans being sited in these zones. For example mains fans must be at least IPX4 rated and a 30mA RCD must be protecting the circuit. Alternatively SELV fans can be fitted. Qualified electricians will ensure the correct type of fan and wiring is installed in accordance with IET wiring regulations. 

For greatest effectiveness, your fan should be as far as possible from the source of replacement air (i.e. an internal door in a bathroom) and generally as high as possible. You can install extract fans in the ceiling but should make sure there are no joists, pipes or cables in the area above the site. 

You will also need to consider any ducting and venting issues, which is usually a job best left to professionals. If you are having a fan fitted into a window, it is important to check that the window size and type is suitable for the unit. A professional glazier will be able to advise and cut the requisite hole. You will also want the fan to be somewhere it can be easily accessed for maintenance and any repairs. 

Extractor fans can be ideal for extracting stale, polluted, or damp air out of individual wet rooms, such as kitchens, bathrooms, wet rooms and utility rooms. Without extractor fans, bathrooms can be prone to condensation, which can lead to damp and the growth of black mould. The moist, damp air in the wet rooms can also migrate around the rest of the property, causing issues in other rooms. Extractor fans can also be useful for removing odours and freshening up the room, which can be important if your toilet is in the bathroom. It is important to install an extractor fan in your wet room or bathroom in order to stop the build up of excess moisture and keep your whole home healthy and well ventilated. 

Every property is different and each property has their own ventilation requirements, what works for one won’t necessarily work for the next. It’s very important to ensure that you properly look into the different options, installing a whole house solution may seem daunting but it will also mean any damp or mould issues will no longer be a problem.   

EnviroVent offer a free home survey as standard to ensure the correct product is installed. During a free home survey your local expert will assess any condensation, damp and mould problems that you may be facing in your property and take readings of the relative humidity levels throughout the property.

All our ventilation specialists are highly trained in carrying out home surveys to identify any underlying problems and make recommendations to ensure the correct solution is provided, all complying with current Building Regulations.