What are the pitfalls of Positive Input Ventilation? The experts reveal this ventilation type's downsides

While Positive Input Ventilation has many advantages in the home when it comes to controlling humidity, it isn't a 100% perfect solution.

No-one wants condensation, damp and mould in their home and PIV can help, but it may not always be the perfect fit, as Michael Zohouri, Founder of Pyramid Eco explains, “While PIV units can address certain ventilation problems, they’re definitely not a one-size-fits-all solution. Their reliance on strategic vent placement, internal airflow management, and maintenance needs makes them less practical for some households.”

Here we look at the Positive Input Ventilation pitfalls to help you decide if it is a ventilation system that will or won’t work in your home. And whether or not you should make it part of your home ventilation mix.

Larry Soper

Currently Larry heads up Envirovent's Technical Support Team as well providing internal and external training on ventilation, regulations and specification, including managing Envirovent's NICEIC approved assessment centre.

Positive Input Ventilation pitfalls

Positive Input Ventilation isn’t a home ventilation system that will work for all dwellings. It has plenty of pluses, but here Soper runs through some of the potential downsides that you need to be aware of if you are thinking of installing Positive Input Ventilation.

1. Initial high costs

The price of PIV units are not as budget -friendly as some ventilation options, but by the same token they are more cost effective than others as Soper explains, “The initial outlay on a PIV system can be more expensive than extractor fans, but less expensive than a centralised extract or MVHR System.”

But you won’t need to spend big on their upkeep, he adds, “Many PIV systems require minimal maintenance and maybe only a filter change, like these Nuaire Drimaster Replacement Filters from Amazon, as and when required.”

2. Not a complete solution

While PIV can be a complete ventilation solution for some properties, it isn’t for all. You often need additional ventilation options as Soper explains, “PIV can be a complete solution for some dwellings, other dwellings may require continuous extract fans as well.”

But this will depend on other factors as he continues, “This can depend on the layout, size and occupancy of the dwelling. PIV will work well with most dwellings where all wet rooms are accessible from the central hall, where the diffuser is fitted without the need of extractor fans.

He adds, “Dwellings with internal wet rooms or wet rooms remote to the diffuser, will require continuous extract fans as well.”

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3. Installation costs

Installing a Positive Input Ventilation system is not a job for the average DIYer, ideally you need a trained professional to install it as Soper shares, “Systems should be installed by persons experienced and competent to do so.” This will add to the overall cost of introducing Positive Input Ventilation into your home. A supplied unit and labour costs will be around £800-£1000.

4. Can be costly to run

PIV units are not typically expensive to run, but a heated unit will cost more to run than a basic unit (and typically an extractor fan) and will add to your energy bills. And it will depend on other factors as Soper explains, “Running costs of PIV units with a heater can vary vastly from dwelling to dwelling, and is dependent on the location, size, layout and climate.”

But, the extra costs on your energy bills can negate other maybe costly issues as Soper adds, “You will get the benefits of improved indoor air quality and reduced costs on redecoration and repair work.” Due to the reduction in mould and damp.

5. You usually need a loft

Typically you need a loft space to take advantage of Positive Input Ventilation as Soper reveals, “The most common PIV unit is a loft mounted system”. But, if you live in a flat or don't have a loft space you have to look for a different type of unit he continues, “There are also inline and wall mounted units suitable for dwellings with airtight lofts or no loft space at all.”

But these don't have all the advantages of a loft mounted PIV unit, “However, the benefits of solar gain will not be available with these products.” Solar gain is the heat gain you get in a loft in the warmer months.

6. Limited control over output

“PIV units are a fit and forget system, designed to run in a background mode and to be automatic in their functionality, " explains Soper. He adds that adding a user to the equation can be an issue, “Having a system when the end user has control over settings can cause issues if the operation is not fully understood (increased costs, noise or inadequate airflow resulting in condensation and mould).”

However, Soper shares, “Many systems now have some form of controllability for the end user if required. Wireless controllers and even app versions, making it suitable for those who do understand the operation and wish to have greater control."

7. They can make your house cold

A loft installed PIV unit draws air from a loft space, so in the colder months a PIV can make your house feel cold as it draws colder air. On the reverse side in the summer months it will draw in warmer air to raise the temperature.

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Michael Zohouri

Michael Zohouri founded Pyramid Eco in 2011, evolving the company from property maintenance to a leader in sustainable retrofitting for social housing. With a passion for energy efficiency and ventilation, Michael is committed to creating healthier, more sustainable homes while addressing key challenges like thermal bridging and air quality.

FAQs

Do Positive Input Ventilation units need regular maintenance?

Yes they do as Zohouri explains, “PIV units do require regular upkeep, even though they’re frequently recommended as low-maintenance systems.” He continues, “The filters typically need replacing every 2–5 years, depending on the air quality in your home.”

Zohouri recommends regular checks on the unit itself, “To keep the unit running efficiently, it’s a good idea to do an inspection every year or two to make sure there’s no dust or debris accumulating around the motor.”

As for servicing he suggests, “While some manufacturers recommend servicing every five years, this isn’t regular enough, especially in homes with higher levels of airborne particulates.”

What problems can a PIV unit help solve?

While a Positive Input Ventilation system can have a lot of plus points it might not always be the perfect fit for a home. Zohouri says, “Without a PIV unit, homes can face common issues like condensation, dampness, poor air quality, stale air, and even potential health concerns related to mould and humidity.”

He adds, “However, PIV units aren’t the only – or necessarily the best – solution for these problems.”

Positive Input Ventilation can work well as part of a ventilation mix in the home. But, Zohouri suggests it needs to work with other types of ventilation. “For condensation and damp, improve natural ventilation by opening windows and installing extractor fans in moisture-prone areas like kitchens and bathrooms can often be more effective.”

To improve air quality he recommends , “Air purifiers with HEPA filters can target specific pollutants and allergens, offering a more precise approach to improving indoor air quality.”

He finishes by saying. “Tackling the root causes of moisture and dampness – such as leaks or insufficient insulation – is crucial for creating a healthy indoor environment. Otherwise, you’re just fixing the symptom and not the cause.”

Ventilation in the home is all part of reducing moisture in the air. It can help tackle window condensation, which can lead to unwanted and ugly mould. Check out our guides on removing mould from walls and how to remove mould from grout in bathrooms and kitchens for a better looking and healthier home.