FAQs on air filters-answers from an air filtration expert

There is a lot of good information on air filters and air filtration systems on the internet. However, there are also a lot of myths. For example, did you know that even if an air filter looks dirty, it may still have plenty of life left? Also, not all air filters are made equal. The quality of the media used in filters, as well as the overall design, affects the filter’s longevity and possible energy savings. In this article, we will be taking an in-depth look at these issues and much more as part of our two-part series with Canadian air filter expert Berni Baier.

How often should you perform maintenance on an air filter?

In a commercial setting, air filters should be checked every three months. This should be sufficient unless you are in a highly contaminated area, for example, with construction or some demolition occurring nearby.

In an industrial setting, air filters can last three months on rooftop units. Still, if your company has an internal process with many contaminants, sometimes maintenance staff may have to check filters weekly.

Air filters being replaced should be examined when new filters are installed. When they have reached their end-of-life, in a particular application, it is best to take note of the lifespan and, after a few changeouts, set an estimated timeline for changeouts as long as conditions remain the same.

If you install an air filter and see that it’s clogging up every two weeks, you should check it weekly to establish a changeout schedule because it’s likely a heavy-use application requiring more frequent maintenance.  

Why is it important to maintain air filters properly? -What are the benefits?

The main benefits of proper air filter maintenance are maintaining good indoor air quality and airflow throughout the air filtration system, allowing for appropriate heating and cooling distribution. If filters get clogged up, you cannot get good airflow through the air handling system, and coils may freeze (at any time of the year), or motors may burn out. 

Another critical thing to keep in mind is that if filters are in service too long, there is a chance they can blow out and get sucked into the air handling system. If that happens, it can clog up the coils. Fibres from filter media can quickly go downstream and get stuck on coils and get sucked into fans, ruining them. Another danger is that particles and filter materials can blow through ducts and end up in offices and other work areas. Workers then breathe in dangerous particles, or they can end up in or on products being manufactured, contaminating them. 

Leaving air filters in too long will lead to much more energy consumption in variable frequency drive (VFD) applications, as airflow is restricted, and fans must work harder to compensate. Performing timely changeouts with high-efficiency air filters can help you achieve your energy savings goals and contribute to the longevity of HVAC equipment. As air filtration systems run smoother when clean, they require less maintenance. Air circulation is essential for maintaining building comfort. Proper air filter maintenance ensures good air circulation. 

What are some important things to remember when servicing and maintaining air filters?

  • Make sure that gaps in the air filtration system are eliminated. Any gap will allow particles to bypass the filtration process, especially if you’re using a high-efficiency filter.
  • Install air filters correctly. Pleated filters should always have the pleats running vertically, not horizontally. Pleats running vertically make the filter stronger and reduce the chance of it collapsing, bending, or bowing out.
  • Use the correct air filters. People often mix and match filters or use the same filter in front and behind to try and improve efficiency. If you have a two-stage filtration system, the secondary filter should always be a higher efficiency than the first filter.
  • The first filter is a prefilter that filters out larger particles over 1 micron before they reach the second stage. This prolongs the life of the main filter and protects equipment by keeping it cleaner. The main filter removes much smaller, more harmful particles such as PM2.5 and PM1.
  • Most applications go with two-stage filtration, with a high-efficiency secondary stage filter, MERV 14-A to MERV 16-A. If installing a MERV 14-A or 16-A efficiency filter is possible, it is best to use a single-stage process, incorporating a bag filter, giving you higher airflow and a lower pressure drop.

What methods could be used to determine when to replace an air filter? 

A lot of people will look at an air filter and see that it’s dirty and want to change it. If a filter is dirty, it’s not that the filter is not doing its job; it’s quite the opposite. A filter is meant to get dirty. There are better ways of determining when a filter should be changed than the ‘eye test.’

A better way to determine if a filter has reached the end of its life, is to look for minor bowing. Properly constructed filters are rigid, but after a certain point, they’ll start bowing slightly if there’s not too much humidity. If you start seeing a bow in the filter, it means the filter is likely reaching a point where it must be replaced.

The best way to determine when a filter needs to be changed is to use a pressure gauge, such as a Magnehelic gauge, on the system so that you know exactly when to change it out. The pressure gauge will show you the resistance to the airflow, and once a filter reaches a one-inch maximum, for example, on a pleated filter, that’s when you have to change it.

To save energy, change the filter at about twice the initial pressure drop. If you wish to maximize the filter’s life and are not so concerned with saving energy, run the filter all the way up to the manufacturer’s final recommended pressure drop before you change out the filter.

What happens if you don’t change your air filters on time?

If you don’t change your air filters at the right moment, filters can become clogged, restricting airflow, leading to poor indoor air quality and higher energy consumption because fans must work harder to cool or heat a building. Filter blowout can cause significant issues downstream in the system. 

Do better-constructed air filters make a difference?

Better construction is advantageous for many reasons. The main reason is lifespan. If you use a filter that’s been appropriately pleated, is strong enough, and has all of its surface area open to the airstream instead of the pleats being bunched up, you will have a lower pressure drop. When all the media in the filter is being utilized, it lasts longer. If a filter has media that is bunched up and, as a result, only utilizes half of the media, the filter will load much faster. Patches of clean media should not be visible on used pleated filters.

Another consideration is the strength of the filter’s frame and its backing. Many filters use a weak expanded metal grid backing. If the filter incorporates expanded metal, make sure it features a heavier gauge metal. A high-quality wire grid backing is solid and resilient and will maintain the shape of the filter and the shape of the pleats.

Lastly, the frame itself is crucial. With a strong beverage board frame design that is water resistant (filters can get wet or humid from the humidification system) it will last longer than a standard cardboard frame. 

Conversely, is it better to buy cheap air filters to save money?

In applications where air filters are changed out frequently, e.g. in pharmaceutical applications where it’s mandated that filters be disposed of frequently due to changes in a process, then it makes sense to use lower-cost filters. Still, it is essential to ensure the filter maintains the expected efficiency. If a MERV-8 filter is required, ensure it’s a MERV-8-A tested filter for maintained efficiency throughout the filter’s life. In an application where the longest filter life and lowest average pressure drop are desired, high-capacity, pleated filters with high-quality media provide the longest life and the lowest energy usage.

Why are MERV-13 air filters in such high demand?

Years ago, consensus was reached in the air filtration industry and by medical officials that the minimum efficiency required to remove submicron particles harmful to human health was MERV-13. It was concluded that natural defences could filter out larger particles.

However, while MERV-13 filters were in high demand, many air handling units were not designed for proper 6″ or 12″ deep, secondary filters as they had one or two-inch tracks. Some filter manufacturers then developed coarse-fiber filters (mainly synthetic media) that were electrostatically charged to bring them to a MERV-13 rating. The problem with this manufacturing method is that even though an air filter may be rated MERV-13 when new, as the charge starts to deteriorate, you may soon be left with a filter that would only test at a MERV-8-rated efficiency. A MERV-8 filter is a far cry from a MERV-13 regarding indoor air quality. Look for a MERV-A rating to ensure it is tested to perform as a true MERV-13 filter. See more on MERV air filter ratings 

What are the advantages of pleated filters versus non-pleated or pad filters?

The main differences are in lifespan, pressure drop, and efficiency. Pleated filters feature more media, offer lower pressure, and last longer. Pleated filters usually start at a MERV-8 efficiency. Pad filters typically begin at a lower efficiency, have a higher pressure drop, and have a much shorter lifespan. 

How do pleated air filters work?

Pleated filters usually come in 11 (Standard Capacity) or 15 (High Capacity) pleats per linear foot. A 15-pleat-per-foot filter using the same media as an 11-pleat-per-foot filter will last longer and have a lower average pressure drop. Adding more than 15 pleats per foot could have the opposite effect, as the full media cannot be utilized due to the media bunching up.  

How do high-quality air filters help to save labour costs?

Definitely, the higher the quality of the filter, the longer it will last. Coupled with a prefilter, a standard bag filter will last anywhere from six months to a year. If you use a high-quality bag filter such as a Hi-Flo ES®, you can expect a filter life of one year without a prefilter. A Durafil® can last three to five years with proper prefiltration. 

Using longer-lasting filters means maintenance personnel don’t have to go up to a rooftop air handling unit very often. Filters should be checked annually, but changeouts may not be necessary for three to five years. This is especially desirable if you use stairways during changeouts or if you use elevators or hoists to bring the filters up to the rooftop and bring the used filters back down. This can be a considerable time and cost saver, allowing for the reallocation of labour for more pressing issues.

To consult with an air filtration expert on the topics covered in this post or for further information, please use this contact form and an air filtration expert from Camfil Canada will answer any questions you may have. 

About Camfil Canada Clean Air Solutions

For 60 years, Camfil has been helping people breathe cleaner air. As a leading manufacturer of premium clean air solutions, we provide commercial and industrial systems for air filtration and air pollution control that improve worker and equipment productivity, minimize energy use, and benefit human health and the environment. Read more about Camfil Canada


Source: air filtration expert Berni Baier 

Media Contact:

Phillip Ilijevski

Camfil Canada Inc.

T: 437-929-1161

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