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Why is ventilation so important?

Traditionally, UK dwellings have relied on wind-driven air in and out to provide adequate ventilation, i.e. to expel “stale” air (containing pollutants such as moisture and high concentrations of carbon dioxide), to provide a supply of “fresh” (i.e. external) air.


Since the 1970s the installation of double-glazed, draught-stripped windows, the draught-stripping of external doors and the insulation of lofts and cavity walls have improved energy efficiency but also reduced the air permeability of many homes, reducing infiltration and air leakage.


In some cases, this has been compensated for by introducing intermittent extract ventilation fans into “wet” spaces (kitchens and bathrooms) to expel moist stale air and by installing background ventilators (air inlets, commonly known as trickle ventilators) in other spaces to provide balancing supplies of fresh air. However, the existence of a ventilation system is not proof that a building is adequately ventilated, and many existing buildings are not adequately ventilated.


Improving the air-tightness of a dwelling to reduce wind-driven air in and out, when combined with adequate controlled ventilation, significantly improves energy efficiency.


However, without adequate ventilation, the installation of any additional insulation anywhere in the building reduces the in and out air flow rate and increases the risk of high relative humidity (which carries a risk of condensation and mould growth), high concentrations of pollutants such as carbon dioxide and dust mites. All of these can contribute to serious health risks for occupants or potential damage to building finishes, fabric and structure.


When installing any insulation measure the adequacy of the existing ventilation shall be assessed and if necessary improved.




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Do I have adequate ventilation?

For the purposes of claiming funding for any insulation install an acceptable, complete ventilation system shall one of the following:

  • an intermittent extract ventilation (IEV) system consisting of correctly sized extract fans in all “wet” rooms and correctly sized background ventilators (to admit “fresh” external air) in all living spaces and bedrooms;

  • a passive stack ventilation (PSV) system consisting of passive stack ventilators serving all “wet” rooms, and correctly sized background ventilators (to admit “fresh” external air) in all living spaces and bedrooms;

  • a continuous positive input ventilation (PIV) system that supplies “fresh” air, combined with correctly sized background ventilators (to allow moist `stale’ air to escape) in all living space and bedrooms;

  • a continuous mechanical extract ventilation (MEV) system that extracts moist, “stale” air from all “wet” rooms combined with correctly sized background ventilators (to admit “fresh” external air) in all living spaces and bedrooms;

  • a whole-house supply and extract MVHR system that extracts moist “stale” air from all wet rooms, supplies “fresh” eternal air to all living spaces and bedrooms, and has been properly commissioned and balanced.


If you already have one of the above and it is deemed adequate at survey then no additional ventilation work will be required.

However, if you don’t or the existing ventilation arrangement is deemed inadequate, we will have to fit additional ventilation solutions in your property in addition to the insulation work.

In living areas not deemed “wet rooms” we will fit air-box vents to openable windows which take around 5 mins per vent to install, don’t require any drilling and are fitted from inside. No mess, no damage and totally controllable air flow in and out.

In “wet rooms” we will fit extractor fans of adequate size and design to pull “stale” moist inside air out of your property.  

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Air-Box® air valves

Why fit them?

Condensation on windows is the first sign of deterioration of the home microclimate; increased humidity contributes to the spread of fungi, bacteria and mould. The cause is generally poor ventilation.

Mould and fungi are dangerous to health. Fungal spores lead to the occurrence of allergic cough, bronchitis, headache, nausea and other unpleasant sensations.

With ventilation, there is always associated heat loss. Through open windows, heat loss occurs tens of times faster than with the Air-Box system®.


The Air-Box system® ensures air exchange in accordance with the standard LBN 231-15 "Heating and ventilation of residential and public buildings". The system is really useful as its fast to fit without any need to cut the window profile.

The Air-Box system® includes

  • noise protection

  • cleaning of incoming air from pollen, dust, spores and soot.

    • Fresh air gets into the channel between the frame and sash in places where standard sealing rubbers are replaced with special ones.

    • Air flow is controlled with the adjuster handle, which ensures a smooth and even adjustment of the air supply.


Fresh air reduces the occurrence of allergic reactions and other diseases. From a medical point of view, the Air-Box system® ideal for young children, the elderly, people with allergies and asthma.

The system also reduces heat loss and makes a significant contribution to saving money on your heating bills.