Types of filters used in HVAC systems

HVAC stands for heating, ventilation, and air conditioning. HVAC systems are responsible for controlling the temperature, humidity and overall air quality in indoor environments, as well as keeping indoor spaces safe and comfortable for occupants.

The filters in these systems play a crucial role in protecting your HVAC system from larger particles that could cause damage, so it’s essential to not only use the correct filter but also replace it when it becomes dirty. There are a variety of options to choose from, with the filter’s performance indicated by its MERV (Minimum Efficiency Reporting Value) rating, which goes from 1 to 20 – the higher the MERV rating, the more effective the filter is at filtering out smaller particles (although high MERV-rated filters may restrict airflow).

In this article, we’ll look at the different types of filters used in HVAC systems, their individual benefits, applications, and how to maintain them.

Types of filters used in HVAC systems

Let’s take a quick sprint through the six different filters and their uses..

1. Fiberglass filters

Fiberglass filters are among the most commonly used and cost-effective HVAC filters. They are designed to capture larger particles such as dust and dirt and are typically disposable and should be replaced every 30 days – although the replacement frequency may vary depending on air pollution levels.

One of the main advantages of fiberglass filters is their affordability, making them suitable for budget-conscious users. They are also easy to replace and do not hinder the airflow in your HVAC system, allowing it to operate efficiently. However, with a low MERV rating of 1-4, fiberglass filters are less effective than other types and allow smaller particles to pass through. This makes them less suitable for individuals with allergies or respiratory conditions.

Fiberglass filters are ideal for homes or offices with low levels of airborne pollutants. They offer a budget-friendly option for those looking to improve air quality but are not recommended for environments with moderate to high levels of pollutants.

2. Pleated filters

Pleated filters, made from materials such as polyester or cotton, are more effective than their fiberglass counterparts due to their larger surface area, allowing them to capture more particles. These filters are available with MERV ratings ranging from 5 to 16.

Pleated filters with MERV ratings from 5 to 8 are classified as medium filters and are the most common in residential HVAC systems. Filters with MERV ratings between 9 and 12 are more efficient, capable of capturing smaller particles, including some bacteria and viruses, making them suitable for commercial or medical office settings.

High-efficiency filters, with MERV ratings from 13 to 16, can capture even smaller particles like smoke, smog, and some viruses. These are often used in hospitals, laboratories, and other high-risk environments. For most households or offices with moderate levels of pollutants, pleated filters with MERV ratings between 8 and 13 are a good choice. They are also beneficial for individuals with mild allergies or respiratory issues. These filters are available in various thicknesses, ranging from 1 to 12 inches.

3. Bag filters

Bag filters are made from synthetic fibres like polyester or fiberglass and are formed into a bag-like shape. They are commonly used in commercial and industrial environments, including hospitals, cleanrooms, and manufacturing facilities where there is a need to eliminate fine particulate matter such as dust, dirt, and pollen from the air. The air enters the bag filter through an inlet, passes through the filter media where particulates (microscopic airborne particles suspended in air) are trapped, and then exits as clean air through an outlet.

Bag filters come in various sizes and filtration efficiencies and can be used as standalone units or as part of a larger air filtration system. They are often utilised in HVAC systems to enhance indoor air quality and protect sensitive equipment from dust and other particulates. Bag filters of 12 to 15 inches deep allow for a higher MERV rating without causing a significant pressure drop, which is a common issue with 2- to 4-inch pleated filters.

Regular maintenance and replacement of bag filters are crucial for proper functionality. Over time, the filter media can become clogged with particulate matter, reducing the filter’s effectiveness, so replacing it regularly is a must.

4. Electrostatic filters

Electrostatic filters are composed of a series of metal plates or grids that are electrically charged. As air passes through the filter, particles in the air become charged and are drawn to the charged plates, where they are captured.

One of the main benefits of electrostatic filters is that they can be washed and reused, unlike traditional disposable filters. Electrostatic filters are particularly beneficial for households or offices with high levels of airborne pollutants. They are also suitable for individuals with moderate to severe allergies or respiratory issues. In industrial applications, similar electrostatic filters (albeit much larger) are used for pollution control (dust, smoke, etc).

Electrostatic filters can be more expensive than traditional filters and often require professional installation. Additionally, they may generate ozone, which can be a concern for individuals with respiratory issues. It is advisable to consult an HVAC professional to determine if an electrostatic filter is suitable for your requirements.

5. HEPA filters

HEPA filters are the most efficient type of HVAC filter, designed with interlaced fibres that capture tiny particles like pollen, pet dander, and bacteria. With a MERV rating of 17-20, HEPA filters are considered the highest-performing in terms of particle filtration.

These filters are ideal for environments with extremely high levels of airborne pollutants, and for individuals with severe allergies or respiratory conditions. However, HEPA filters are very costly, and the HVAC system must be specifically designed to accommodate them for proper operation. They are commonly used in laboratories, clean rooms, and operating rooms where air quality standards are essential.

6. Potassium permanganate filters

Potassium permanganate is a potent oxidising agent which is used to remove impurities from the air. These types of filters operate by air passing through a filter media containing the chemical, which then reacts with and oxidises contaminants, trapping them in the filter. They are effective against VOCs, sulfur dioxide, and other odorous gases.

These filters are often used in commercial and industrial settings such as laboratories, hospitals, and manufacturing plants to eliminate VOCs, odours, and harmful gases. However, they are ineffective at removing particulate matter like dust and allergens, and potassium permanganate can be hazardous if mishandled. Regular maintenance and replacement are crucial for their proper function.

Conclusion

Selecting the right filter for your system is crucial for ensuring optimal air quality and system performance. The appropriate filter can capture contaminants such as dust, pollen, and bacteria, improving indoor air quality and protecting the health of occupants, especially those with allergies or respiratory issues. So, it’s always worth speaking to an expert to determine which filter is right for you.

Daikin is a world leader in HVAC systems, offering a wide range of solutions tailored to meet diverse building requirements – including residential, commercial, and industrial. Daikin offers a full lineup of split systems, packaged units, ductless mini-split systems, VRF (VRV) systems, and more – each designed to deliver exceptional performance, energy efficiency, and comfort. 

With innovative, pioneering technology and exceptional service, Daikin has sold millions of systems in 140 countries. If you would like to find out more about Daikin’s products, contact us today.