When it comes to ensuring fresh air in our homes and removing indoor pollutants, UK Building Regulations Part F outlines the essential requirements for ventilation in new and existing homes. One key element is Purge Ventilation, addressed in sections 1.26 to 1.31 of the document. While the traditional method relies heavily on opening windows and doors, there is a growing case for mechanical alternatives that provide more comfort, efficiency, and control.

It is also important to note that purge ventilation does not remove the need for independent ventilation requirements in kitchens, utility rooms, bathrooms and other wet rooms. These are still mandatory in line with Part F of the building regulations, starting at section 1.17. Purge ventilation requirements are an additional requirement for improved indoor air quality in all homes, especially more modern built homes with higher air-tight construction.

What is Purge Ventilation?
Purge Ventilation, as defined in Part F (1.26–1.31), refers to the rapid removal of indoor air pollutants, excess moisture, or heat build-up, particularly during activities like painting, cooking and cooking mishaps like burning food, or overheating in summer. The guidance typically recommends large openings, such as windows or external doors, to achieve the necessary air changes per hour (ACH) for effective purging.

The regulations specify:

• Minimum openable areas based on the floor area of the room or dwelling (generally 1/20th of the floor area).
• The importance of direct access to the outside.
• Special consideration for overheating and indoor air quality in airtight, energy-efficient homes.

While effective in principle, relying solely on manual opening of windows and doors for purge ventilation has several drawbacks in real-world settings.

The Problem With Opening Windows and Doors.
Although it's the simplest method, opening windows and doors for purge ventilation can introduce several issues, especially in modern living:

1. Noise Pollution: Homes located near busy roads or in urban centres may experience unacceptable levels of outdoor noise when windows are open.
2. Air Pollution: Outdoor air can carry harmful particulates, NOx emissions from traffic, and allergens, particularly problematic for those with respiratory issues.
3. Heat Loss: In colder months, opening windows can rapidly decrease indoor temperatures, leading to discomfort and higher heating bills.
4. Pollen Infiltration: Especially in spring and summer, open windows allow pollen indoors, affecting allergy sufferers.
5. Home Security Risks: Leaving doors or windows open, even briefly, can compromise home security, particularly in ground-floor rooms or densely populated areas.

Mechanical Ventilation: A Better Way to Purge
To address these limitations, mechanical ventilation systems offer a smart alternative for purge ventilation. These solutions ensure effective air changes while providing a much higher level of control and comfort. Common systems include:

1. Mechanical Extract Ventilation (MEV & dMEV)
A centralised or decentralised system that extracts stale air from “wet” rooms (kitchens, bathrooms) and/or living spaces (living rooms, dining rooms, bedrooms and hallways) and vents it outside. It helps quickly clear moisture and pollutants without opening windows, although a return of air is required to balance the air pressure in the home via passive trickle vents.

2. Mechanical Ventilation with Heat Recovery (MVHR & dMVHR)
MVHR systems extract stale air and simultaneously supply filtered, fresh air from outside. Heat from the outgoing air is recovered and transferred to the incoming air, significantly reducing energy loss. Most MVHR and dMVHR units have a manual purge setting that forces the unit into its highest airflow configuration to meet the air movement requirement for purge ventilation.

3. Purge Fans (High-Rate Extract Fans)
Some homes use dedicated high-capacity extract fans to purge specific rooms rapidly. These fans are often activated manually or by sensors and can meet purge airflow requirements in compliance with Part F. In general, larger 6 inch/150mm high-powered inline fans are suitable for this task, but will generally only vent from one room of the home.

Benefits of Mechanical Purge Ventilation
Adopting mechanical ventilation for purge purposes provides several clear advantages:

• Reduced Noise Intrusion: No need to open windows means less traffic and neighbourhood noise.
• Improved Air Quality: High-grade filters remove particulates, allergens, and pollution from incoming air.
• Energy Efficiency: MVHR systems retain heat, reducing the energy needed to reheat fresh air.
• Allergy Reduction: Filters keep pollen and other allergens out, improving indoor health.
• Enhanced Security: All ventilation occurs through sealed, tamper-proof systems, not open windows.

Final Thoughts
While traditional purge ventilation methods comply with Building Regulations, they often conflict with the goals of comfort, energy efficiency, and indoor air quality. Mechanical solutions offer a modern, more effective, secure, healthy and compliant alternative that meets the same ventilation objectives - but with added benefits that suit today’s building standards and lifestyles. Whatever mechanical ventilation option you choose, you can enjoy the benefits of a controlled environment without the downsides of opening windows.

In general, the best option is a system that supplies filtered air as well as extracts - this will maximise your protection from outdoor airborne pollutants entering your home. MVHR is ideal as it will cover your home with one system, but is ideally installed during construction or a major renovation, as installation is very intrusive. Alternatively, dMVHR or single room heat recovery units are a much easier option for an existing build. However, as single-room systems, multiple units may need to be installed to meet whole-house purge requirements. Both options here have the downside of initial high costs, but the savings in heating costs in winter months and the protection from pollutants all year round and overheating in the summer months will outweigh this initial inconvenience.

Alternatively, MEV or dMEV units can be a less costly install, but you will rely on a return of outside air via trickle vents or, in older buildings, through the natural gaps in the fabric of the building - this will also be the case with specific purge fans - so not filtration options here.

Below are a list of links to the fans we recommend for each of the extraction options as well as a link to our MVHR specification site should this option be suitable for you:

MVHR
Contact us to discuss MVHR systems - we offer a free specification service to identify and design the right system to meet your home's specific needs to meet all regulations and building control requirements.

dMVHR
Blauberg Vento-Maxi Single Room Heat Recovery Unit - multiple units can be installed throughout the home, which can all link wirelessly to work together.

MEV
Vent Axia 443298 MVDC-MSH Whole House MEV with Humidistat - has automatic boost via humidity sensor as well as two switched live connections, allowing for a dedicated manual purge switch. The extraction rate can be adjusted, allowing for independent trickle, humidity boost, switched live 1 and switched live 2 speeds to be set by the user.

dMEV
Silent Tornado ST100DMEVS dMEV - Ideal for living spaces, this version of the popular Silent dMEV from Tornado has fully adjustable trickle and boost speeds, allowing for quiet background extraction and a wired switch to manually boost the fan to purge when required. No over-run timer or humidistat means complete control for the user and no disturbances due to automatic boosting.

Purge Fans (High-Rate Extract Fans)
Tornado TT150PROS - High-powered inline fan option. Larger units are available, but this is a great place to start if you are looking for a single, central & dedicated inline unit for purge ventilation.

You can visit the current Building Regulations Part F for more information on domestic ventilation requirements.