Filtration FAQs

For optimal performance we recommend changing the air filters in your air handling unit at least every six months. Pre-filters on dusty sites often need changing every 3–6 months, while secondary bag filters usually last 6–12 months. The best guide is the pressure drop across each filter bank – we can fit gauges and offer condition-based monitoring so filters are changed when they need it, not before.

Filters are now graded to ISO 16890 (ISO Coarse, ePM10, ePM2.5 and ePM1), which replaced the old EN 779 G, M and F classes. A typical AHU uses a coarse pre-filter (old G4) to protect a finer secondary filter (old F7, roughly ePM1 50–65%). High-care food areas, laboratories and cleanrooms may need HEPA filters (H13/H14 to EN 1822).

We’ll check your unit, the space it serves and any audit requirements and recommend the right grades.

There is no single UK figure for air quality in food factories. The BRCGS Food Safety standard expects air in high-risk and high-care areas to be controlled by risk assessment – the right filter grades, positive pressure where needed, and documented filter changes, cleaning and maintenance. We provide the service records auditors ask for.

As filters load with dust the resistance to airflow rises, so the fan has to work harder (or airflow drops). Changing filters at the right pressure drop, choosing low-resistance filters and keeping coils clean all reduce running costs – we can carry out energy surveys on your AHUs.

Yes. Filter frame, damper, fire damper, fan and motor, plug fan and heating / cooling coil replacements are all part of our AHU remedial and refurbishment work – often a cost-effective alternative to a new unit. See AHU refurbishment.

A Local Exhaust Ventilation (LEV) system captures harmful airborne contaminants – dust, fume, mist, vapour or gas – at source, before they reach the people working nearby, and carries them away to a filter or a safe discharge point. It is a key control measure under COSHH.

COSHH regulation 9 requires a thorough examination and test of LEV at least once every 14 months. Some processes listed in Schedule 4 of COSHH need testing more often (as often as monthly), and records of each test must be kept for at least five years. We provide LEV testing and can put your system on a regular schedule so it never lapses.

Normally around 6 to 12 months, but it depends on the dust type, the volume of air and how many hours the system runs. Rising differential pressure, poor capture at the hoods or dust at the clean-air outlet are signs the filters need attention.

Fine powders, heavy or abrasive dust, sticky or oily mist and welding fume all need different filter media, cleaning systems and duct velocities. Many dusts – wood, flour, sugar and some metals – are also combustible, so DSEAR / ATEX requirements apply. Tell us about your process during the free site survey and we’ll specify the right equipment.

Yes. As well as dust collectors we install, service and repair extraction for oil mist from machining, process fume and spray – the same principles of capturing at source, filtering and maintaining apply.

Ask for evidence. Our engineers carry CCNSG safety passports and IPAF and PASMA training for work at height, we are CHAS accredited and SafeContractor approved, and we provide RAMS before work starts.

We recommend cleaning your air handling units at least every six months to maintain efficiency and hygiene – more often in high-care food areas, where the cleaning schedule should be set by your risk assessment. Coils, drip trays, filter sections and fan chambers are the main places dirt and moisture collect.

It depends on the dust and how much is produced. Build-up in ducts reduces airflow at the hoods and, with combustible dust, increases fire and explosion risk. We check ducting during maintenance visits and recommend cleaning when it is needed.

A full inspection of filters, coils, fans, dampers, belts and bearings, cleaning, filter replacements, performance testing (airflow, temperatures, humidity), diagnostics and recommendations. See AHU & dust collector maintenance.

There is no single law, but employers must keep ventilation systems clean and in good repair, and BESA’s TR19 is the recognised UK specification for ventilation hygiene. Insurers and auditors (for example BRCGS) expect cleaning to be planned and recorded.

Keep a record of every filter change, clean, service and LEV test. We provide service paperwork for each visit, and existing customers can access their documents through our customer portal.

Fabric ducting (also known as air socks or textile ventilation) is air distribution ducting made from polyester material. It spreads air evenly and draught-free along its length, which suits food production, laboratories, warehouses and sports halls.

Yes. We expertly measure on site, supply the right fabric ducts or air socks for your system and fit them for you – including replacing old, worn or damaged socks.

Not on their own. Fabric ducts distribute the air – heating, cooling and humidity are controlled by the air handling unit that feeds them. Choosing the right fabric and outlet pattern does help avoid draughts and condensation.

Most fabric ducts can be taken down and laundered, which is important in food production. Over time seams, joints and fixings weaken – we can inspect them, take them down and refit them, or supply replacements.