Filters
Air filters for ventilation and extract systems — G4 pleated panel filters, F7 bag filters, in-line duct filter boxes and stainless steel baffle grease filters, supplied from UK stock by Alpha Air in Leicester. Filtration protects fans, coils and ductwork, keeps supply air clean and, in kitchen extract, stops grease building up in the duct run. Stocked filters ordered by 3pm are despatched for next-day delivery.
Panel, bag and inline filters
- G4 pleated panel filters — the workhorse pre-filter for air handling units and ventilation plant. Available in 1 inch, 2 inch and 4 inch depths across a wide run of standard imperial face sizes (for example 20 x 16 x 1 and 24 x 24 x 4), so replacing existing panels is straightforward.
- F7 bag filters — fine filtration for supply air systems, used as a second stage after a G4 panel to capture finer dust and particulates.
- Inline filter boxes — duct-mounted filter housings with EU3 filter media, in diameters from 100mm to 315mm. They drop straight into a round duct run to protect inline fans and keep systems clean, and the media can be replaced without disturbing the ductwork.
- Stainless steel baffle filters — washable grease filters for commercial kitchen extract canopies, built to take the heat and cleaning regime of a working kitchen.
How do I choose the right filter grade?
G4 is the standard coarse grade for protecting equipment and general ventilation; it captures the bulk of visible dust. F7 is a fine grade used where supply air quality matters — offices, commercial buildings and anywhere fresh air is delivered to occupied spaces, usually with a G4 panel in front of it to extend its life. Baffle filters are not graded the same way: their job is to strip grease from kitchen extract air before it enters the duct.
Check the depth and face size of your existing filter before ordering — panel filters are usually labelled in inches on the frame. If you are matching a filter to one of our inline filter boxes, choose the box diameter to match your spiral ducting.
Keeping systems maintained
Filters are consumables: a blocked panel starves the fan, raises energy use and can shorten motor life, so most sites change G4 panels on a regular cycle and keep spares on the shelf. Ordering replacement filters in multiples is the easy win — the panel sizes here are standard across air handling plant, so one order can cover every unit on site. Baffle filters, by contrast, are washable and re-usable; keep a spare set so extraction never has to stop while a set is being cleaned. As a Leicester-based UK supplier we hold stock locally, next-day delivery applies to stocked filters ordered by 3pm, and UK mainland delivery is free on orders over £400 ex VAT — lead times for non-stocked sizes are shown on each product page.
Types of Air Filters
Panel Filters
Panel filters (also called pre-filters or coarse filters) are the first line of defence in a ventilation system, capturing large particles such as dust, pollen, and fibres. They are typically rated G3 or G4 and are used in general ventilation applications or as pre-filters ahead of finer secondary filters. Panel filters are available in standard sizes for common air handling units and can be cut to size for custom applications.
Bag Filters (Pocket Filters)
Bag filters provide a higher filtration grade (typically F5 to F9) with greater dust-holding capacity than panel filters. The multiple pockets create a large filter surface area in a compact frame. They are commonly used as secondary filters in commercial HVAC systems where a higher standard of air quality is required, such as offices, hospitals, and clean environments.
HEPA Filters
HEPA (High Efficiency Particulate Air) filters capture 99.97% of particles at 0.3 microns. They are used in critical environments including operating theatres, pharmaceutical manufacturing, cleanrooms, and laboratory ventilation. HEPA filters require careful handling and installation to maintain their seal integrity.
Carbon Filters
Activated carbon filters remove odours, gases, and volatile organic compounds (VOCs) from the air. They are commonly used in kitchen extraction systems, paint spray booths, and industrial processes where chemical or odour removal is required.
Filter Maintenance
Regular filter replacement is essential for maintaining system performance and indoor air quality. Clogged filters restrict airflow, increase energy consumption (the fan works harder to overcome the resistance), and can lead to poor air quality and system damage. Most commercial systems should have filters checked monthly and replaced quarterly, or more frequently in dusty environments.
Why Choose Alpha Air?
We stock replacement filters in common sizes for immediate dispatch and can source specialist filters to order. Contact our team on 0116 246 0031 for help identifying the correct filter for your system.
Frequently Asked Questions
How often should air filters be replaced?
As a general guide, panel pre-filters should be replaced every 1-3 months and bag/fine filters every 6-12 months, depending on the environment. Dusty or polluted environments require more frequent changes. Most modern air handling units have a differential pressure indicator that signals when the filter needs replacing.
What filter grade do I need?
G3/G4 panel filters are suitable for general ventilation and protecting downstream equipment. F5-F7 bag filters provide good air quality for offices and commercial spaces. F8-F9 is used in hospitals, laboratories, and clean environments. HEPA (H13/H14) is for critical applications such as operating theatres and cleanrooms.
Can I wash and reuse air filters?
Some washable panel filters are designed to be cleaned and reused, but most disposable filters (especially bag filters and HEPA filters) must be replaced when spent. Washing a disposable filter damages the media and compromises filtration performance. Always check the manufacturer’s instructions for your specific filter type.