Why do HVAC filters matter?
The filter is the cheapest yet most effective part of a climate control system. A filter of the right class and kept clean protects coils and fans from dirt, improves indoor air quality and lets the system run at its design airflow. A clogged filter, on the other hand, increases fan energy, reduces airflow, and causes coil icing and loss of efficiency. A filter that is installed incorrectly or has a leaking frame lets dirty air bypass it around the filter, defeating the filtration.
- Cleaner indoor air and less dust
- Lower fan energy consumption
- Longer life for coils and fans
- Maintaining the design airflow
- Hygiene requirements in hospitals and clean rooms
- Protecting electronic equipment in data centers
Filter classes: from EN 779 to ISO 16890
For many years, general ventilation filters were classified under the EN 779 standard as G (coarse), M (medium) and F (fine). In 2018 this standard gave way to ISO 16890. ISO 16890 rates a filter by the share of real particle sizes (PM10, PM2.5, PM1) it captures. Since both classifications are still used together in the field, the table below gives an approximate comparison.
| EN 779 (legacy) | ISO 16890 (approximate) | Particles captured | Typical use |
|---|---|---|---|
| G3 – G4 | ISO Coarse 60–90% | Coarse dust, pollen, fibers, insects | Pre-filter, split and fan coil filter, air handling unit first stage |
| M5 | ePM10 50–60% | Coarse and medium-size dust | Intermediate stage in office air handling units |
| M6 | ePM2.5 50–65% | Fine dust, most pollen | Commercial buildings |
| F7 | ePM1 50–65% | Fine particles, part of the soot | Final stage in office, school and hotel air handling units |
| F8 | ePM1 65–80% | Fine particles | Buildings requiring high indoor air quality |
| F9 | ePM1 80–90% | Very fine particles | General hospital areas, pre-HEPA stage |
In hospital operating rooms, clean rooms and laboratories, high-efficiency filters classified under EN 1822 / ISO 29463 are used. These filters are tested at the most penetrating particle size (MPPS).
| Class | Efficiency (MPPS) | Typical use |
|---|---|---|
| E10 – E12 (EPA) | %85 – %99,5 | Sensitive process areas, pre-HEPA |
| H13 (HEPA) | at least 99.95% | Operating rooms, intensive care, clean rooms |
| H14 (HEPA) | at least 99.995% | Sterile areas, pharmaceutical production, critical clean rooms |
| U15 – U17 (ULPA) | 99.9995% and above | Semiconductor and specialized clean room applications |
HVAC filter types
| Type | Construction | Advantage | Point to watch |
|---|---|---|---|
| Panel (cassette) filter | Cardboard or metal frame, pleated or flat | Inexpensive, easy to replace; G3–G4 pre-filter | Short service life; frame sealing |
| Washable filter | Aluminum or synthetic mesh | Reused in split and fan coil units | Clogs quickly if not washed regularly |
| Bag filter | Multi-pocket synthetic or glass fiber bag | Large surface, long life; M5–F9 | Pockets must hang upright and open |
| Compact (V-bank) filter | V-shaped pleated packs | Low pressure drop, high efficiency; F7–F9 | Heavy; frame gasket is critical |
| Roll filter media | Cuttable synthetic felt | Adapted to custom sizes | Requires correct cutting and fixing |
| Activated carbon filter | Carbon-impregnated media or granules | Captures odors and gases | Odor returns once saturated; used together with a dust filter |
| Nanofiber cassette filter | Nanofiber filter media, rigid cassette frame | Fits in the G4 slot and replaces the F5–F7 bag stage; washable, service life up to 5 years | Regular washing according to the dust load of the environment |
| HEPA filter | Micro glass fiber, with separators or mini-pleated | Highest particle capture | Always protected by a pre-filter; seating and gasket test |
| Grease (hood) filter | Labyrinth-type metal | Captures grease in kitchen exhaust | Frequent cleaning; fire safety |
Nanofiber filters and nanofiber cassette filters
Nanofiber filters use a filter layer made of fibers much finer than one micron in diameter (typically in the hundreds of nanometers). Because the fibers are so fine, the pores between them are also very small; this lets fine particles be captured on the filter surface.
In classic filters, particles are captured by becoming embedded inside the media (depth filtration), and pressure drop rises quickly as the filter fills. In a nanofiber layer, most particles stay on the surface (surface filtration). That is why the filter can be cleaned by washing and operates with lower pressure drop at similar efficiency: the fan is strained less and energy consumption falls.
What is a nanofiber cassette filter?
A nanofiber cassette filter is a ready-made filter module in which nanofiber filter media is placed inside a rigid cassette frame. It replaces a standard G4 cassette filter and fits in the same slot. This way, without changing the duct, unit or filter cell, you move to a filter that captures much finer particles in the place of the G4 pre-filter.
Key features
- Fits directly into a standard G4 cassette filter slot
- Removes the need for a separate F5, F6 and F7 bag filter stage
- Washable; does not deform as it is washed
- Rigid construction keeps its shape and fit
- Offers a service life of up to 5 years
- Saves fan energy with low pressure drop
- Reduces frequent filter purchases and waste filters
- Used in all HVAC, ventilation and air conditioning systems
One filter, two stages
In air handling units, fine filtration is usually done in two stages: a G4 pre-filter followed by an F5, F6 or F7 bag filter. Bag filters cannot be washed, are renewed regularly, and themselves create a significant pressure drop. A nanofiber cassette filter fits in the G4 slot and provides this fine filtration in a single stage; a separate bag filter stage is no longer needed.
| Feature | G4 cassette + F5/F6/F7 bag filter | Nanofiber cassette filter |
|---|---|---|
| Number of stages | Two stages (pre-filter + bag) | Single stage |
| Installation location | G4 slot + separate bag filter cell | Standard G4 cassette slot |
| Fine particle capture | According to the bag filter class | Replaces the F5–F7 bag filter stage |
| Cleaning | Cannot be washed, replaced | Washable, does not deform as it is washed |
| Construction | Bag pockets must hang upright | Rigid cassette construction |
| Service life | Bag filters are usually replaced every 6–12 months | Up to 5 years |
| Pressure drop and energy | Combined pressure drop of the two stages | Single stage, low pressure drop |
| Waste and consumable cost | New filter and waste at every replacement | Washed and reused |
Where is it used?
- Air handling units
- Fan coils
- Heat pumps
- Chiller condensers
- Precision air conditioners and data centers
- Ventilation and heat recovery units
- Cassette, ducted and VRF indoor units
- All HVAC, ventilation and air conditioning systems
On chiller and heat pump condensers, a nanofiber cassette filter in front of the coil captures dust, pollen and fibers and reduces condenser fouling; as long as the coil stays clean, condensing pressure stays low and efficiency is maintained.
At YOİ Mühendislik, we measure your existing G4 cassette filters, supply nanofiber cassette filters in the suitable size, install them, and add the washing interval to your maintenance schedule.
Which filter is used where?
| Application | Recommended filter stage |
|---|---|
| Home and office split air conditioner | Washable pre-filter; optional carbon or fine filter accessory |
| Fan coil | G3–G4 panel or washable filter |
| Office, school and shopping mall air handling unit | G4 pre-filter + F7 final filter, or a single-stage nanofiber cassette filter in the G4 slot |
| Hotel and high indoor air quality | G4 + F7/F9, activated carbon if needed |
| General hospital areas | G4 + F7 + F9 |
| Operating room and intensive care | G4 + F7/F9 + terminal HEPA H13/H14 |
| Clean room and pharmaceutical production | Pre-filter + F9 + H13/H14 (depending on class) |
| Data center and precision air conditioning | G4 or F7 (per the equipment manufacturer's recommendation) |
| Industrial kitchen exhaust | Metal grease filter, carbon if necessary |
| Parking garage and exhaust fans | Usually unfiltered; G4 at the fresh air intake |
When should the filter be replaced?
Filter replacement is ideally tracked not by the calendar but by differential pressure (the pressure difference between the front and back of the filter). The manufacturer of each filter gives an initial and a recommended final pressure drop; the filter is replaced as it approaches this value. Installing a differential pressure gauge (manometer) on air handling units removes the guesswork about when to replace the filter.
| Filter | Approximate check / replacement interval | Note |
|---|---|---|
| Split and fan coil washable filter | Wash every 1–3 months | Monthly in a dusty environment |
| G4 panel pre-filter | Usually 2–4 months | According to differential pressure and ambient dust |
| F7–F9 bag or compact filter | Usually 6–12 months | Lasts longer if the pre-filter is replaced regularly |
| Nanofiber cassette filter | Washing according to the dust load of the environment; service life up to 5 years | Does not deform as it is washed |
| HEPA H13/H14 | Usually 1–3 years | According to differential pressure and validation results |
| Activated carbon | When odor returns or per the manufacturer's service life | Earlier if the dust load is high |
| Precision air conditioner filter | Usually 3–6 months | According to the filter alarm |
Filter-related problems and solutions
| Symptom | Likely cause | Solution |
|---|---|---|
| Weak air discharge | Clogged filter | Filter cleaning or replacement; differential pressure check |
| Icing on the coil | Low airflow, dirty filter | Filter replacement, coil cleaning, refrigerant check |
| Increase in electricity consumption | High pressure drop, strained fan | Filter replacement; switching to a low pressure drop filter |
| Bad odor | Damp and dirty filter, saturated carbon filter | Filter replacement, drain and pan cleaning |
| Increased dust in the space | Frame leakage, wrong class, torn filter | Gasket and seating check, filter of the right class |
| Torn bag filter | Excessive pressure, no pre-filter | Adding a pre-filter stage, replacement |
| Filter alarm on precision air conditioner | Clogged filter or faulty differential pressure sensor | Filter replacement, sensor check |
| High particle count after HEPA | Gasket leak or damaged filter | Seating and gasket check, filter replacement, retest |
Our filter service
- Determining the class and size of existing filters
- Supply of custom-size panel, bag, compact, nanofiber cassette and HEPA filters
- Filter replacement for air handling units, fan coils, split and precision air conditioners
- Installation of differential pressure gauges (manometers)
- Frame, gasket and seating check
- Replacement schedule and documented reporting
- Coil and drain pan cleaning
- Periodic replacement under the annual maintenance contract
In areas that require validation, such as hospitals and clean rooms, we plan HEPA filter replacement in line with the facility's testing and validation process.
Our headquarters is in Etimesgut, Ankara. We work with a daily field team in Ankara and with a planned team from Ankara in other provinces, on a project, annual maintenance contract and public tender basis. See the areas we serve.
Frequently asked questions
What is the difference between a G4 and an F7 filter?
G4 is a pre-filter that captures coarse dust, pollen and fibers. F7 is a final-stage filter that captures fine particles. In air handling units, a G4 pre-filter is usually used together with an F7 filter to protect it.
What is ISO 16890?
It is the international standard that classifies general ventilation filters by their efficiency in capturing PM10, PM2.5 and PM1 particles. It replaced the old EN 779 standard in 2018.
How often should a split air conditioner filter be cleaned?
Usually every 1–3 months, depending on how heavily it is used. In dusty environments and during peak season, monthly cleaning is recommended.
What happens if the filter is not replaced?
Airflow drops, the fan uses more energy, the coil gets dirty and may ice up, and indoor air quality gets worse. In the long run, the fan motor and compressor are also strained.
Is installing a higher-class filter always better?
No. A higher-class filter creates more pressure drop; if the fan cannot handle it, airflow drops. The filter class should be chosen according to the fan capacity and the needs of the application.
Can you supply filters in custom sizes?
Yes. We determine the size and class of your existing filter, supply a custom-size panel, bag, compact or HEPA filter, and carry out the replacement.
What is a nanofiber filter?
It is a filter medium made of very fine fibers (hundreds of nanometers in diameter). Because it captures particles mainly on the surface, it can be cleaned by washing and operates with lower pressure drop at similar efficiency.
Can a nanofiber cassette filter be installed in my existing air handling unit?
Yes. A nanofiber cassette filter replaces a standard G4 cassette filter and fits in the same slot. We measure your existing filter and supply the suitable one.
Is a bag filter still needed when using a nanofiber cassette filter?
No. In a G4 slot, a nanofiber cassette filter provides the fine filtration of an F5, F6 and F7 bag filter stage; you do not need to use a bag filter as well.
Is a nanofiber cassette filter washable, and how long does it last?
Yes, it is washable, and thanks to its rigid structure it does not deform as it is washed. It offers a service life of up to 5 years.
Can a nanofiber filter be used instead of HEPA?
No. A nanofiber cassette filter is a general ventilation filter. In areas that require HEPA it can be used as a pre-filter, but a HEPA filter is required at the terminal stage.