Types of Filters Used in HVAC Systems

The most common HVAC design filter types are fibreglass, pleated, bag/pocket, electrostatic, HEPA, activated carbon, and UV. The different types protect different designs. For example, pleated and fibreglass filters are designed to provide equipment protection. Bag filters protect AHUs, while HEPA filters protect hospitals and laboratories by removing fine particles. Carbon filters protect buildings from unpleasant odours, and UV lights protect against microorganisms. There is no one best HVAC filter type, but a choice depends on the MERV rating, the airflow, the building type, and the budget.

What is an HVAC system?

HVAC stands for Heating, Ventilation, and Air Conditioning. The HVAC system’s meaning is simple: it is the combined equipment that heats, ventilates, and cools a space while controlling air quality. It’s a combination of different technologies. HVAC systems mean heating, ventilation, and air conditioning, and controlling air quality, airflow, and temperature. Filter systems are at the forefront of HVAC systems. The HVAC system works on a feedback system and uses the air return system and the supply system, with air travelling between them, passing through filter systems, fans, cooling and heating coils. 

What are the different filter types used in HVAC designs?

If your cooling bills and stuffy rooms weren’t enough, consider that many facility managers and owners get what they pay for with the filters they pick. They pick based on price, then become annoyed as dust returns quickly after replacement. The guide below provides the types of filters used in HVAC design to ensure the filters fit the space, the budget, and the airflow.

In typical HVAC system designs, air goes through the return system, hits a filter bank, and goes to the heating and/or cooling coil, through a supply system with air supply nozzles, through the rooms, and back to the return system. A simple HVAC system diagram shows this path: return air, filter bank, heating/cooling coil, fan, supply ducts, rooms, and back to the return. In almost every HVAC system diagram for an AHU, the filter bank sits at the start of the path, ahead of the coils.

For this reason, filters in these HVAC designs are usually before the cooling and/or heating coils. In most large HVAC systems used in building construction, multiple air handling units (AHUs) hold one or multiple stages of filters, whereas smaller HVAC fan coil units (FCUs) usually contain a single-stage filter. An HVAC system in building projects is usually split between central AHUs, which hold one or more filter stages, and smaller FCUs, which usually contain a single-stage filter.

Types of Filters Used in HVAC Systems

The table below summarises the types of filters used in HVAC system applications, from lowest to highest efficiency.

1. Fibreglass Filters

The filters are cheap, easily replaced, and are composed of spun glass. Their frame is composed of cardboard. Because of the filter’s low restriction on airflow, they will keep your air systems working at low load. However, the filters do a poor job of air cleaning. The reason for their poor air cleaning is due to their MERV rating of 1-4, which allows for smaller particles to easily pass through the filters.

2. Pleated Filters

This type of filter consists of either polyester or cotton material, folded over. The folded material is similar to other flat media but has a significantly larger surface area, which helps these filters capture and hold a large amount of dust and have a longer filter life than other filters on the market. Manufacturers report that this type of filter has greater strength than filters with a thinner material. Because of this, they are great to be used as a primary or a pre-filter within the AHU.

3. Bag (Pocket) Filters

Bag filters, often referred to as pocket filters, utilise deep fabric pockets for capturing dust and handling air that flows at a high rate. Most pocket filters serve as the secondary filter stage in an AHU, often within hotels and offices and also shopping centres. Pocket Filters’ long, deep construction allows more time between changes and also necessitates a large space for the filter house.

4. Electrostatic Filters

The most commonly utilised method for electrostatic filtration is through the application of a static charge to capture the filter media particles. There are multiple variations of this filtration method, and they can be washed or thrown away. These systems are used both within residential and commercial spaces, and while effective, have an increased noise profile and must be cleaned on a more frequent basis than alternative solutions.

5. HEPA Filters

HEPA filters are the most advanced type of filtration within the industry. This is due to their ability to capture smaller particulates that can’t be captured by standard filters. Hospitals, labs, and clean rooms are typical locations for this type of filtration. Their high level of filtration comes at the price of reduced airflow; thus, they must be integrated into custom-designed systems. For safety, used filters must be handled while wearing a mask and gloves.

6. Activated Carbon and UV Filters

Adsorbent carbon filters trap odours and VOCs. This makes them ideal for labs, industrial sites and kitchens. UV lights, meanwhile, are great for sterilising air by killing off bacteria, viruses, and similar germs. Filters in both cases work best in combination with particulate filters.

Choosing the Right Filter

With the right filter, you get better equipment protection, better indoor air quality, and better energy efficiency. It has been noted by the Department of Energy of the United States that having an air conditioning system with a clean, brand-new filter as opposed to one that is clogged can improve an air conditioner’s energy consumption by as much as 15 percent. This saving can be sustained every month, especially in areas with warm weather where cooling is run for the better part of the year.

• Poorly selected or neglected filters can cause the following:
• Uneven airflow and less than ideal temperatures
•  Clogged evaporators with diminished heat absorption.
• Faster breakdown and reduced lifespan of equipment
• Worse indoor air quality for users.

A filter’s performance is graded using a system called MERV (Minimum Efficiency Reporting Value). As MERV ratings increase, filters are more effective at trapping particles, but they require higher air velocity through the fan. Consequently, you must ensure that your HVAC filter is appropriate for the system.

Choosing the Right HVAC Filter: Step-by-Step

Following a prescribed sequence of steps simplifies selecting an HVAC filter from the options available.

1. Identify the system type. Different system types (e.g., split unit, FCU, AHU, and packaged) will accommodate different sizes and thicknesses.
2. Determine the filter size and housing. Make sure to note how many stages of filters your unit uses and measure the dimensions of the filter space, or consult the existing filter.
3. Define the goal. Consider whether you need protection of the equipment, allergen removal, removal of odours, or sterile air.
4. Select a MERV range. MERV 1-4 meets general requirements. MERV 8-13 provides more sophisticated protection for most comfort situations. Critical health or surgical protection requires even higher MERV ratings, typically above 13.
5. Come up with a filter change schedule. Examine your filters and replace as necessary. Dirty filter replacements become more frequent with animals, dust, and constant system use.
6. Write it down. Put it in your HVAC maintenance log, including the type, size, and when the filter was changed.

Filter Replacement Example

An example to help explain (not an actual result). There were issues with the AC at a mid-sized office space because there were issues with the fibreglass filter. The cooling was uneven, and there were complaints about dust. To resolve these, a pleated pre-filter and bag filter combination was used, and an inspection schedule was created for every two months. This greatly reduced the need to clean the cooling coil, reduced complaints about the AC being uneven, and there was no dust. Two filters are better than one when the fans are correctly set up and checked.

Price and Replacement Intervals

Generally, the higher the filter efficiency, the higher the filter replacement effort. For most filter types:

1. Fibreglass: Least expensive. Replace at approximately 1-month intervals.
2. Pleated: Lower- to mid-cost. Replace at approximately 1-3 month intervals.
3. Bag/pocket: Mid- to high-cost. Replace at approximately 3-6 month intervals.
4. HEPA: Most expensive. Replace at approximately 1-3 year intervals depending on pre-filters.

These are typical intervals and depend heavily on environmental conditions, such as excessive dust or high moisture levels, and on how much the system is used. Contact local UAE filter suppliers for current prices and for temporary UAE project HVAC requirements, you may consider rental equipment with filter maintenance services. For temporary projects, HVAC system rental UAE options are available, and many rental providers include filter maintenance in the service.

Filters, VCDs and Retro-Commissioning

Filtering also requires balanced airflow for maximum efficiency. A VCD in HVAC system design (a volume control damper) regulates how much air reaches each branch. If the dampers of your volume control system aren’t correctly set, filtering will become inefficient, and your air supply to the rooms will become severely reduced. That is why the role of a VCD in HVAC system balancing matters as much as the filter itself.

There are many reasons to consider HVAC system retro-commissioning for an older system, including reduced energy use, increased user comfort, fewer system breakdowns, and clear records of damper and coil conditions. Many of the symptoms you may be experiencing can be corrected, like frequent clogging of filters and inconsistent airflow.

HVAC System Maintenance Tips for Filters

Proper HVAC system maintenance can extend the life of your filters and keep them operating at maximum efficiency. Use these guidelines to maintain your filters:

1. Check filters on a monthly basis, especially with systems that have high airflow.
2.  Do not operate your system without a filter.
3. When you purchase a replacement, make sure that it matches both the size and the airflow rating of your current filter.
4.  Create an airtight seal around your filter frame to eliminate air leaks.
5.  Make an appointment to have coils, drains, and ducts cleaned professionally at least once every six months to a year.

Frequently Asked Questions

Q1. Which kinds of HVAC filters are typically used in commercial installations?

These kinds are fibreglass, pleated, bag (pocket), electrostatic, HEPA, activated carbon, and UV filters. Their ratings of filter efficiency are each designed for different airflow levels and types of buildings.

Q2. Which kind of filter is best suited to a commercial HVAC installation?

A two-stage configuration of a pleated filter, followed by a bag filter, works best for most office environments and shopping malls. Medical and scientific buildings utilise HEPA filters. Kitchens and commercial settings utilise carbon filters.

Q3. How would you describe a MERV rating?

MERV stands for “Minimum Efficiency Reporting Value”. It describes the ability of the filter to remove particles. Higher MERV numbers describe a filter’s ability to remove more and smaller particles from the airstream.

Q4. How Often Do I Change HVAC Filters?

Inspect your system monthly and replace the filter when it gets dirty. Fibreglass and pleated filters, the most common type of filter, should be changed every 1 to 3 months, or more often if your environment is very dusty or your system runs a lot.

Q5. Can I use a HEPA filter in my HVAC system?

No. Because HEPA filters significantly reduce airflow, systems must be specially designed to use them. Installing one in a standard system would put undue stress on the fan and degrade cooling efficiency.

Q6. Do Dirty Filters Increase Energy Bills?

Yes. According to the US Department of Energy, installing a clean air conditioning filter can save 5 to 15% on energy costs.