PUBLIC HEALTH INFORMATION*:
Loft-mounted positive-input ventilation
What is loft-mounted positive-input ventilation?
In-loft PIV is installed in a loft space and is advertised as a ventilation solution for condensation, damp and mould.
The machine extracts air from the loft space through a filter and delivers it through ceiling vents into the living space.
Lofts are not designed as controlled environments. They are often exposed to airborne particulates and biotoxins including dust, mould, insulation fibres, rodent or bird droppings, all of which can be drawn into the PIV system and delivered directly into the home’s living areas. An environmental change - such as a rodent moving in or a roof leak - can have an impact on the air quality within hours.
"Particles that can't be filtered pose the greatest health risk."
World Health Organisation
Are PIVs suitable for homes?
As standard, in-loft PIV systems use G4 filters, which filter particles larger than 10 μm. Mould spores are 2-40μm and mycotoxins - the microbial volatile organic compounds (MVOCs) released by some spores - are 0.1μm.
By the World Health Organisation’s definition: “ultra-fine or nano-particles pose the greatest health hazard, as they can cross the alveolar-capillary barrier, enter the lungs directly via the bloodstream and consequently spread to organs, including the brain.”
Disclaimer: Indoor Air Aware is making no claims relating to any brand or technology. This campaign relates to and communicates information provided by first-hand experiences associated to be linked with the installation of the technologies mentioned.
Shared experiences - stories from families
The Shepherds
The Shepherd family rented a council property in Devon. After reporting condensation issues - despite good heating and ventilation behaviours - the council instructed a third party property management company to install an in-loft PIV. The Shepherds explained that the ventilation company didn't survey the loft, but went ahead and fitted the PIV. The loft space was mouldy due to water entering via the old leaking roof.
After a few weeks of the in-loft PIV being fitted and activated their youngest daughter - Elizabeth, aged 10 months, whose bedroom was next to the vent, became very sick and went into anaphylaxis and rushed to hospital.
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Louisa
Louisa's rental property had water leaks from the roof affecting the internal walls. Louisa reported that, instead of fixing the structural issues, the landlord fitted a positive input ventilation system into a mouldy, damp loft. Within weeks of the PIV being fitted, Louisa reported that her health declined, resulting in brain fog, chronic fatigue, skin conditions, and facial swelling. Symptoms reduced when Louisa left the property.
Louisa has reported that her possessions were contaminated by the mould, leaving her homeless and unable to take any belongings with her. Louisa is now recovering in a new property and is able to continue her important work as a phlebotomist.
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Shelley & family
Shelley flagged high moisture and mould issues to her landlord. While researching solutions online, she saw a PIV advertised as delivering fresh, filtered air. She suggested this as a solution to the landlord.
The landlord agreed and a local tradesman installed it.
Within weeks Shelley and members of her family said they noticed a variety of physical and neurological health symptoms and suspected it may be the air from the PIV causing the issues - the only obvious environmental change.
After employing the services of Dr Suhail Ahmed - a highly-skilled environmental scientist, the evidence was very clear. See below.
Dr Suhail Ahmed Investigation
"When we attended the property, the PIV unit had been switched off as previously arranged. We carried out our Stage 1 protocol, which included a visual assessment and air sampling. Once this was completed, the PIV was switched back on and we assessed the air being delivered into the living space. During this check, the airborne fungal particle levels in the supply air appeared elevated, which was a concern because a PIV should ideally supply clean, filtered air rather than introducing additional particulates into the home."
Dr. Suhail Ahmed BSc, MSc, PhD Senior Environmental Scientist
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Are you experiencing symptoms?
People react differently to mould because our bodies, brains and immune systems are unique. Smell perception varies hugely between individuals: some people have a very sensitive sense of smell and can detect the musty compounds mould releases at extremely low levels, while others simply don’t register them at all. On top of that, prior exposure, genetics, allergies, asthma, and immune responses all influence how the body reacts. For some, mould triggers headaches, fatigue or breathing problems long before it’s visible; for others, there may be little or no immediate reaction.
Symptoms of poor air quality can range from chronic fatigue, to skin rashes, and migraines to hair loss. Any health symptoms that alleviate during time spent away from your home may be linked to the home itself.
If you think you have been impacted by mould email contact@indoorairaware.co.uk for more information.
Response from ventilation manufacturers / installers
After gathering experiences and health impacts associated with the installation of in-loft PIV, Indoor Air Aware met with a handful of UK manufacturers of the technology to request changes in the interest of public health.
We requested, at the meeting in August 2025, that:
1) All in-loft PIV products to be discontinued
2) A health advisory to be sent to everyone who has purchased an in-loft PIV / has an in-loft PIV installed
During the meeting the manufacturers acknowledged the real-life experiences and the mycology evidence and tentatively agreed to improving the following features:
1) Improved filters as standard
2) Better loft-survey advice to installers
3) Health advisory
However, six weeks later we received an official response from manufacturers via BEAMA, that was disappointing. During this time BEAMA requested more evidence, but we explained that we felt the evidence provided was sufficient.
The correspondence said:
HEALTH ADVISORY
In a significant number of cases, this is not practical because manufacturers do not know where these systems are. I also do not believe it is a realistic proposition to send such a communication to customers without a sufficient body of evidence and/or any legal ruling to base such an action on. I cannot conceive of any manufacturer across any technology group or sector that would undertake this action.
POTENTIAL IMPLICATIONS - Any households whose health has been impacted by in-loft PIVs will remain unaware of the potential cause. The manufacturers are waiting for a legal ruling or more evidence before taking action.
SURVEY
I can confirm that in discussion with manufacturers they have agreed to review their instructions to ensure it is clearly stated that a full loft survey is required before installation to ensure supply air is safe. We would note that manufactures only propose the use of loft PIV in a properly ventilated loft already, which is covered in Part C of the Building Regulations and references BS5250.
POTENTIAL IMPLICATIONS - Anyone can buy and install an in-loft PIV. There's no guarantee that a survey will be completed at all. This will not guarantee public health and safety.
FILTERS
They have also agreed - over sufficient time taken to address supply chain 'wash through' of existing products using G4 filters - to upgrade the standard filter specification to F7 quality filters if analysis shows that this will reduce risk of effects which are out of manufacturer control.
POTENTIAL IMPLICATIONS - This is a positive response to our campaign, however it is not enough in our opinion. F7 filters can not filter out nanoparticles which are the most hazardous to our health. These filters are more expensive, meaning consumers pay more to maintain a system that cannot filter the most dangerous particles.
ENVIRONMENT
This brings us onto environment. I believe the installed environment will be something of a topic for debate because this is, in the majority of cases, out of manufacturer control and is an issue for the specifier and actors further down the supply chain. As already stated, we can bolster instructions to note the key elements of BS5250 in this regard, but as many PIV units are sold through distribution, again, this is out of our control.
POTENTIAL IMPLICATIONS - This response confirms the uncontrolled distribution and management of the installation of these systems.