Air Filters 101: Types, Materials, and Maintenance

Air filters are an essential part of maintaining good indoor air quality, but with so many types and materials available, it can be overwhelming to choose the right one.

There are several types of air filters, including fiberglass, pleated, and HEPA filters. HEPA filters, in particular, are known for their high efficiency in removing 99.97% of particles as small as 0.3 microns.

When it comes to maintenance, air filters should be replaced every 1-3 months depending on usage and manufacturer recommendations.

Additional reading: Types of Air Filters for Hvac

Air filters come in various types, each designed to capture different sizes of particles.

Coarse filters are used as primary filters and have a particulate size approaching 100% retention of >5 μm.

The European normalization standards EN 779 recognize the following filter classes for coarse filters: G1, G2, G3, and G4, with performance ranging from 65% to 90%.

Fine filters, on the other hand, are used as secondary filters and have a particulate size approaching 100% retention of >5 μm.

Here's an interesting read: High-efficiency Particulate Air Filters

The European normalization standards EN 779 also recognize the following filter classes for fine filters: M5, M6, F7, F8, and F9, with performance ranging from 40-60% to 95%.

Semi HEPA filters, such as E10 and E11, are designed to capture smaller particles, with a particulate size approaching 100% retention of >1 μm and >0.5 μm respectively.

HEPA filters, like H13 and H14, are designed to capture even smaller particles, with a particulate size approaching 100% retention of >0.3 μm.

Here's a table summarizing the different types of air filters and their performance:

Foam is a popular choice for air filters in off-road rallying and other motorsport applications where high levels of dust are encountered. It can offer minimal airflow restriction or very high dirt capacity, depending on the grade and thickness of foam employed.

Oil-wetted polyurethane foam elements are widely used in aftermarket replacement automobile air filters. They're also commonly used on air compressors for air tools up to 5 horsepower.

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Cotton gauze is another material used in air filters, particularly in high-performance aftermarket automotive air filters. Oiled cotton gauze is employed in these filters to provide a high level of filtration.

Stainless steel mesh is a medium that allows more air to pass through, making it a popular choice for extreme modified engines. It comes with different mesh counts, offering different filtration standards.

Foam is a popular material used in air filters, especially in high-dust environments like off-road rallying and motorsport applications. It's oil-wetted polyurethane foam elements make it a great choice for capturing large amounts of dust without restricting airflow.

Foam filters are commonly used on air compressors for air tools up to 5 horsepower. This is because they can offer minimal airflow restriction or very high dirt capacity, depending on the grade and thickness of foam employed.

The way dust is captured on foam filters is a key advantage. Large amounts of dust can be trapped without causing a measurable change in airflow restriction.

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Cotton is a versatile material used in various applications, including automotive air filters.

Oiled cotton gauze is particularly popular in high-performance aftermarket air filters.

Cotton gauze was previously limited to non-automotive uses, but it's now being used in original-equipment automotive air filters, starting with the Abarth SS versions.

Fiat's subsidiary supplies cotton gauze air filters as OE filters, marking a significant shift in the industry.

Stainless steel is a popular choice for applications where high airflow is required, as it allows more air to pass through.

Stainless steel mesh comes in different mesh counts, offering varying filtration standards.

In some extreme engine modifications, a stainless steel mesh is used over the turbo to prevent particles from entering the engine.

This solution is often chosen when there's limited space for a traditional cone-based air filter.

On a similar theme: Stainless Steel Air Filters

High Efficiency filters are a big deal when it comes to removing finer particles from the air. They can remove particles in the 1 to 3 micron range, which is impressive.

MERV ratings of 9 to 12 are considered high-efficiency, but they're still relatively inexpensive. However, filters rated MERV 13 to 16 are highly efficient and remove very fine particles.

True HEPA filters, rated MERV 17 and up, can remove 99.97 percent of particles down to 0.3 microns. These filters are usually only installed in central air systems designed or upgraded to accommodate them.

Some newer homes are designed with central air system ductwork to accommodate true HEPA filters. If you have a central heating and cooling system with filtration, you may want to consider upgrading to a high-efficiency filter.

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Air filters can be used in various applications to improve indoor air quality. They're particularly effective in homes with pets, as they can reduce indoor concentrations of cat and dust mite allergen by up to 60% when using a HEPA filter.

In homes with asthma sufferers, simple low-cost interventions including air filters can lead to significant improvements in health scores. A study found that using a high-efficiency furnace filter (MERV 12) and HVAC service resulted in improved asthma quality-of-life surveys.

Room air cleaners can also be beneficial, especially when used in conjunction with other interventions such as dehumidifiers and dryer exhaust ventilation. However, the most effective interventions relative to symptoms were HVAC servicing with improved air filtration and dehumidifiers, according to the study.

Whole house filtration is a comprehensive approach to improving indoor air quality, and it's a game-changer for people with allergies or asthma. This method involves using a high-efficiency furnace filter in conjunction with a room air cleaner and other interventions.

Studies have shown that whole house filtration can be effective in improving health scores, particularly when combined with other interventions like cleaning and repairing the home to eliminate water intrusion and mold.

A study of 219 children with asthma found that using a high-efficiency furnace filter (MERV 12) and other interventions like room air cleaners, dehumidifiers, and dryer exhaust ventilation resulted in significant improvements in asthma quality-of-life surveys.

The most effective interventions relative to symptoms were HVAC servicing with improved air filtration and dehumidifiers, with room air cleaners also showing benefits.

To give you a better idea of the effectiveness of different filter efficiencies, here's a breakdown of the predicted reductions in indoor mass concentrations for various particle sizes:

It's worth noting that increasing filter efficiencies above a certain point may not result in significant additional benefits, and that airflow exchange rates can be more important than filter efficiencies in achieving good indoor air quality.

The automotive cabin is a vital part of your vehicle, and it's essential to keep it clean and free of allergens.

Cabin air filters, also known as pollen filters in the UK, are typically pleated-paper filters placed in the outside-air intake for the passenger compartment.

Some cabin air filters are uniquely shaped to fit specific vehicles' outside-air intakes.

The first automaker to include a disposable filter was Nash Motors with their "Weather Eye" in 1940.

A reusable heater core filter was available as an optional accessory on Studebaker models starting in 1959.

Clogged or dirty cabin air filters can significantly reduce airflow from the cabin vents and introduce allergens into the cabin air stream.

Clogged filters can greatly reduce the effectiveness and performance of the vehicle's air conditioning and heating systems.

Some cabin air filters perform poorly, and manufacturers often don't print a minimum efficiency reporting value (MERV) filter rating on their products.

Consider reading: Clogged Air Filters

Internal combustion engines use a combustion air filter to prevent abrasive particulate matter from entering the engine's cylinders, where it would cause mechanical wear and oil contamination.

Most fuel injected vehicles use a pleated paper filter element in the form of a flat panel, usually placed inside a plastic box connected to the throttle body with duct work.

Older vehicles that use carburetors or throttle body fuel injection typically use a cylindrical air filter, usually between 100 millimetres and 400 millimetres in diameter, positioned above or beside the carburetor or throttle body.

The overall unit, including the filter and housing, is called the air cleaner.

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The 2nd edition of the guide to air cleaners in the home was published in August 2018.

To select a portable air cleaner, consider the size of the room it will be used in. The guide covers portable air cleaners and furnace or HVAC filters used in a home.

A portable air cleaner can be an effective way to remove particles in a large room. It's available in both HTML and PDF formats, with the PDF version being 2.9 MB.

The guide includes tips for selecting a furnace filter or HVAC filter, which is essential for maintaining good indoor air quality.

On a similar theme: How to Install Air Filters in Furnace

Air filters come in various classes, each designed to capture specific sizes of particles. These classes are crucial in determining the effectiveness of an air filter.

Coarse filters, used as primary filters, are categorized into four classes: G1, G2, G3, and G4. Each of these classes has a different particulate size approaching 100% retention, ranging from >5 μm to >5 μm.

The performance of coarse filters varies, with G1 and G2 filters achieving an average particulate removal of 65% and 65-80%, respectively. G3 and G4 filters have a slightly higher performance, with average particulate removal of 80-90% and 90%, respectively.

Fine filters, used as secondary filters, are also categorized into different classes. These classes are M5, M6, F7, F8, and F9, with each having a different particulate size approaching 100% retention, ranging from >5 μm to >1 μm.

Here's a comparison of the different filter classes:

Semi HEPA filters, which are used in air purifiers, have a higher particulate removal rate than coarse and fine filters. The E10, E11, and E12 classes have a particulate removal rate of 85%, 95%, and 99.5%, respectively.

HEPA filters, which are used in high-end air purifiers, have an even higher particulate removal rate. The H13 and H14 classes have a particulate removal rate of 99.95% and 99.995%, respectively. These filters are designed to capture particles as small as 0.3 μm.

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For a healthy home, it's essential to have the right air filters in place. A good quality air filter can make a huge difference in the air you breathe.

Using a filter rated MERV 10 or higher is a great starting point for a central air system. This will help capture smaller particles and allergens that can aggravate respiratory issues.

Regular cleaning and replacement of air filters is crucial. I've seen dust and debris accumulate quickly if filters are not maintained regularly.

For portable air filters, look for one with a high-efficiency or HEPA filter. These filters are designed to capture 99.97% of particles as small as 0.3 microns.

The California Air Resources Board has a list of certified air cleaners that you can check to ensure you're getting a high-quality filter.