Ruth MacEachern, Product Manager at EnviroVent discusses PIV and MVHR and choosing the right ventilation strategy for healthier indoor environments

As awareness of indoor air quality continues to grow in line with new regulations like Awaab’s Law, ventilation is no longer viewed as a “nice to have” but a fundamental part of delivering healthy, compliant living spaces. Homes today are more airtight than ever, which brings energy efficiency benefits but also increases the risk of trapped pollutants, excess moisture, condensation, and indoor air quality issues if ventilation isn’t properly addressed.

Two of the most commonly specified whole‑house ventilation approaches in UK homes are Positive Input Ventilation (PIV) and Mechanical Ventilation with Heat Recovery (MVHR). While both are designed to improve indoor air quality, they work in very different ways and suit different property types and scenarios.

Understanding how each system functions and where it performs best is key to ensuring the right solution is specified for each home.

How PIV works

Positive Input Ventilation is a whole‑house system that works by gently supplying filtered air into the property, typically from the loft space. This continuous input of air creates a slight positive pressure inside the home, which helps to push stale, moisture‑laden air out through natural leakage points such as trickle vents, air bricks and gaps around doors and windows.

Rather than extracting air mechanically from individual rooms, PIV focuses on dilution and displacement. Pollutants such as excess humidity, odours, airborne allergens and everyday household contaminants are gradually forced out and replaced with filtered air.

Because the air is introduced at a low flow rate and filtered before entering the living space, modern PIV systems operate quietly and unobtrusively, providing background ventilation without relying on occupant interaction.

The indoor air quality and health benefits

PIV can play a particularly valuable role in reducing condensation, damp and mould, which remain some of the most common indoor air complaints in UK housing. Excess moisture generated from everyday activities such as cooking, showering and drying clothes can quickly build up in poorly ventilated homes, creating ideal conditions for mould growth and dust mite proliferation.

By constantly introducing drier external air, PIV helps to stabilise humidity levels across the entire dwelling, reducing surface condensation and limiting the conditions mould needs to thrive. This, in turn, supports better respiratory health, especially for occupants affected by asthma, allergies or other breathing conditions.

Unlike intermittent extract fans, which depend on manual operation or occupancy sensors, PIV systems run continuously, maintaining consistent air movement and improving overall air freshness throughout the home.

When PIV is the best option

PIV is particularly well suited to existing homes and retrofit scenarios, where installing a ducted ventilation system may be disruptive or impractical.

It is commonly specified in:

• Older properties with limited or inconsistent background ventilation
• Homes experiencing condensation or mould but without major structural defects
• Social housing and private rental properties where minimal disruption is important
• Occupied homes where residents need an immediate, low‑maintenance solution

Because installation requirements are relatively straightforward, PIV offers a cost‑effective and scalable way to address indoor air quality issues across large housing portfolios. Its simplicity, reliability and ease of upkeep make it a popular choice where a quick improvement in living conditions is required.

However, it’s important to recognise that PIV relies on the building’s natural leakage paths to expel air. As housing stock becomes increasingly airtight, this is where alternative strategies may be more effective.

Introducing MVHR

Mechanical Ventilation with Heat Recovery operates on a fundamentally different principle. Rather than supplying air into the property and allowing it to escape naturally, MVHR systems extract stale air from wet rooms such as kitchens and bathrooms, while simultaneously supplying fresh air to living and sleeping spaces via a fully ducted system.

What sets MVHR apart is its ability to recover heat from outgoing air. As warm, stale air is extracted, the heat is retained within the heat cell to pre‑warm the incoming fresh air, improving thermal efficiency while maintaining a continuous supply of air. This controlled, balanced airflow allows MVHR systems to manage indoor air quality with a high degree of precision.

Why MVHR delivers long‑term indoor air quality control

MVHR is particularly effective in airtight, modern properties, where uncontrolled air leakage is minimal and ventilation must be carefully managed.

Because air supply and extract rates are balanced, MVHR prevents pressure imbalances within the home, reducing draughts and helping maintain stable internal conditions. The continuous removal of humidity and pollutants directly from source rooms makes MVHR highly effective at reducing condensation and helping to protect the building fabric.

From an indoor air quality perspective, MVHR systems also offer excellent filtration, helping to reduce the ingress of outdoor pollutants and allergens, which are a growing consideration in urban environments.

When MVHR is the right choice

Under Approved Document F of Building Regulations, MVHR is suitable for a dwelling with any air permeability level, however MVHR is often suited to:

• New‑build homes designed to high airtightness standards
• Properties undergoing deep retrofit or whole‑house renovation
• Homes where energy efficiency and occupant comfort are key priorities

While installation is more complex than PIV, the long‑term benefits in terms of comfort, air quality control and energy performance make MVHR a strong choice where design conditions allow.

Choosing the right system

No single ventilation system is right for every property. The most effective solution depends on a range of factors, including:

• The age and airtightness of the building
• Existing ventilation pathways
• Occupant behaviour and lifestyle
• Budget, disruption tolerance and long‑term performance goals

In many existing homes, PIV provides a practical and accessible route to improving indoor air quality and reducing moisture‑related problems. In contrast, MVHR offers maximum control and efficiency for homes designed to support a fully ducted ventilation strategy.

What matters most is that ventilation is considered early, specified correctly, and matched to the realities of the building and its occupants. With indoor air quality now firmly on the agenda, choosing the right approach has never been more important.

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Mould has become the topic everyone is talking about, and not just the housing sector. Since Awaab’s Law was announced, damp and mould have been in the news, and this is having a knock-on effect that is being felt through the supply chain. For electrical wholesalers, ventilation is suddenly a hot topic, and Positive Input Ventilation is flying off the shelves. Andy Inskip, Sales Director at Manrose, explains.

Mould is in the news. With Awaab’s Law coming into force for social housing landlords on 27th October 2025, there has been a huge surge in awareness about the health risks of living with mould. Social housing landlords now have to investigate and fix damp and mould problems within strict timeframes, but the ripple effect has reached beyond the social housing sector. Private landlords and homeowners are now paying attention too, and they are looking for quick, effective solutions. For electrical wholesalers, this means they are seeing a surge in Positive Input Ventilation (PIV).

Nationwide problem

Awaab’s Law was introduced after the tragic death of two-year-old Awaab Ishak, caused by mould in his home. The new legislation aims to stop that ever happening again, forcing social housing landlords to act fast when tenants report damp or mould. Since 27th October 2025, social landlords are required to address damp and mould hazards that present a significant risk of harm to tenants, within fixed timescales. They also have to address all emergency repairs, whether they relate to damp and mould or any other hazard, as soon as possible and within no longer than 24 hours.

While the law only applies to social housing, it has raised public awareness about the dangers of damp and condensation. Homeowners who once ignored black spots on the bathroom ceiling or musty smells are now taking them seriously. Newspapers and social media are now full of mould horror stories, and that is driving consumers to look for preventative solutions, not just a quick wipe with bleach.

Mould is a nationwide problem. The English Housing Survey recently revealed that around 5% of English homes have damp problems, the highest in five years. Condensation is the biggest culprit, affecting 3% of homes overall, and rising to 7% in local authority properties. That is almost a million homes in need of better ventilation

This demand is not slowing down. As Awaab’s Law came in, it highlighted how important it is to keep our homes dry and healthy. The shift in awareness means wholesalers and contractors are increasingly fielding questions about ventilation, condensation and indoor air quality (IAQ). And PIV is becoming the go-to fix.

Positive Input Ventilation

PIV works by drawing fresh filtered air from the loft and gently introducing it into the home. This positive pressure pushes out stale moisture-laden air, reducing condensation and preventing mould from forming.

It is simple, effective and ideal for retrofits, which is exactly what many homes in the UK need. For electricians PIV is a breath of fresh air since it is effortlessly installed. Simple to fit and commission in any size loft, only a hole in the ceiling is needed to fit the diffuser and no external cut outs are needed.

Designed to make both electricians’ and electrical wholesaler’s lives easier, PIV like Manrose’s Lo-Watt Pivotal comes complete with a ceiling diffuser, flexible duct and G4 filters, plus hanging kit and floor mounting base as standard, so there is everything that is needed to complete the installation. Meanwhile, a handle incorporated into the unit makes it easy and safe to carry the PIV which is especially useful when lifting through loft hatches.

The unit is supplied with a diffuser to be installed in a central location within the property e.g. in the main hallway of a bungalow or in the landing in a conventional property. The unit is easily set to the appropriate speed at installation based on the size of the property. Natural leakage points that are present in all properties, as well as purpose provided exhaust points, enhance the air change.

Once the PIV is installed, depending on the property, it could take between a few hours to a few days to start to see the effects and may take a couple of weeks for the areas affected with mould to dry out completely. So, households should be happy with seeing a solution that works so quickly.

Cost of living

Another feature wholesalers should also make electricians aware of is the low running costs of the latest energy efficient PIV. This will make PIV attractive for households in the current cost-of-living crisis. The latest PIV continuously ventilates silently in the background while in ‘Trickle’ mode and uses less energy than a standard lightbulb. They can also recover warmth from the loft air during winter, helping to lower heating bills.

Breathe easy

PIV also provides whole house air purification and humidity control, which adds up to a great solution for households. PIV isn’t just about stopping black mould, it also improves IAQ, reduces allergens and creates a fresher, more comfortable home.

Wholesalers can also reassure their customers that PIV units will not cause an irritating cool draft either. Many units come with a comfort heater which tempers the incoming air. For example, the Lo-Watt Pivotal range includes a heater and non-heater model, the Lo-Watt Pivotal with 500W heater helps reduce the chill as fresh air enters the property.

With this new, increased demand for PIV, being ready with the right stock, product knowledge and advice will make wholesalers a key part of the solution, helping electricians meet demand and helping households breathe easier.

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Wholesalers are witnessing a growth in Positive Input Ventilation (PIV) sales as households increasingly ask electricians for help tackling condensation and mould. PIV is a very effective solution that removes persistent mould and improves indoor air quality (IAQ) and so is a great product for electrical wholesalers to offer. Katie Mairs, Channel Marketing Manager at Vent-Axia, explains more.

Condensation, damp, and mould affect thousands of homes across the UK. More than just an eyesore, these problems can cause serious damage to properties, lead to extensive repairs, and even put health at risk. An ongoing issue for many households, Awaab’s Law has brought the risks of living in a mouldy home into sharp focus following the tragic death of two year old Awaab Ishak. As a result, households are asking electricians, who are completing work in their property, for help in tackling condensation and mould, as well as indoor air pollution. Positive Input Ventilation is a very effective solution that removes persistent mould and improves IAQ and so is a great product for electrical wholesalers to offer.

So, what is Positive Input Ventilation? Ideal for existing properties, PIV offers a whole house ventilation solution that can be installed in the loft. The technology gives wholesalers a highly effective option to offer electricians to help their customers to control condensation and mould in their homes. Designed to remove stale, moist air from the home and replace it with filtered, drier air, PIV prevents moisture buildup that can cause condensation and mould, improving IAQ.

Tackling condensation and mould

Ventilation is condensation and mould’s biggest enemy since it tackles the root cause: moisture in the air. By removing moisture from the air, condensation cannot settle on cold surfaces and mould cannot grow, removing the problem at the source. PIV also provides whole house air purification and humidity control, which adds up to a great solution for electrical wholesalers. Operating by drawing in warm, fresh air from the loft, PIV units, such as Vent-Axia’s PureAir Home, filter all incoming air via high-grade ISO ePM10 or ePM2.5 filters before gently introducing it into habitable areas of a property via a ceiling-mounted diffuser. The diffuser directs the airflow upwards, where the incoming drier air mixes with the warm, moist air that gathers at ceiling height. Providing filtered, tempered air (heater model only) into the home, which is drier than the inside air, the PureAir Home creates an indoor environment where condensation and mould find it hard to exist. This improves IAQ and quickly eradicates conditions that lead to mould growth and associated health issues, such as asthma and itchy skin, as well as avoiding the damaging effects on the building.

Happy households

PIV units like Vent-Axia’s Lo-Carbon PureAir Home are highly energy efficient, unobtrusive, near silent, and help provide a healthy environment. Once installed in a loft, a PIV unit will operate without the household even noticing it is running due to its quiet operation. There are PIV units now available that are near silent in operation; for example, at the point of supply into the house the PureAir Home is almost inaudible. The unit will continuously ventilate silently in the background whilst in ‘Trickle’ mode.

Wholesalers can also reassure their customers that PIV units won’t cause irritating cool draughts either. Many units come with an energy-efficient comfort heater which tempers the incoming air. However, every home is different. This makes fine control of air velocity and heat temperature essential to eliminate cold draughts. Vent-Axia’s PureAir Home, therefore features Smart Sense technology, which allows for 1l/s or 1ºC adjustments to ensure a home’s ideal thermal comfort. Plus, once the unit automatically senses excess heat being lost into the loft, the airflow will increase to ‘Energy Recovery’ mode to recover heat that would otherwise be lost through the roof.

Finally, in the current energy climate, households will be happy to know that the PureAir Home features a quiet-running Lo-Carbon motor and ultra-low power consumption, which works out typically less than a traditional lightbulb to run. Plus, the unit is also made using recycled material, offering a more sustainable choice for households.

Happy installers

Electrical Wholesalers can be assured that PIV offers a simple install for their customers. Vent-Axia’s PureAir home is uniquely flexible offering two installation methods, high-sided anti-vibration legs and a hanging set come as standard, allowing it to be installed quickly in any size loft. If installed on the floor, Vent-Axia’s PureAir Home features unique anti-vibration legs and mounts that eliminate the vibration caused when PIV units are fixed to the joists in the loft, reducing any noise.

Easy to fit, installer safety was a key driver when designing Vent-Axia’s Lo-Carbon PureAir Home. With the unit sized to fit all standard loft hatches, the PureAir Home is a lightweight one-man-lift, with an easy-grip top-mounted handle moulded into the main body, which makes transporting the unit into the loft simple and safer.

Vent-Axia’s PureAir Home is also supplied with a purpose designed diffuser to be located over the stairwell of a conventional dwelling, in the main hall of a bungalow, in the landing or hallway. The four point contact easy fit technology allows fast and repeatable ‘drill free’ installation. Once installed using Smart Sense Technology the unit is easily set to the appropriate speed at installation based on the size of the dwelling.

Helping provide a healthier indoor environment for households, PIV proactively prevents condensation and mould while combating a wider range of indoor air pollutants. Ticking all the right boxes for electricians too, electrical wholesalers can be confident that Vent-Axia’s PureAir Home PIV will tackle condensation and mould, offer easy install, and ensure homeowner satisfaction, so fewer callbacks.

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