How to Spot Airflow Imbalance Between Parallel Filter Banks

If you manage a facility with parallel filter banks, uneven airflow can be easy to miss until pressure drop, dust loading or comfort complaints start to change. The challenge is that one bank can quietly begin doing more of the work while the others contribute less, which can affect filtration performance and make maintenance planning less predictable.

The good news is that there are practical signs to watch for. With the right checks, you can identify imbalance early, understand what is causing it, and decide whether the issue needs cleaning, replacement, rebalancing or a broader system review.

What airflow imbalance means in a parallel bank arrangement

In a parallel arrangement, air should be shared across each bank as evenly as the system design allows. If one bank has a lower resistance than the others, it may draw a larger share of the airflow. If another bank is more blocked, damaged or poorly seated, it may see less airflow and underperform.

That imbalance matters because the whole system is only as effective as its weakest point. If one bank is overloaded, it can load up faster, increase resistance sooner and create uneven service needs across the installation.

Common reasons for imbalance include:

• •different stages of dust loading across banks
• •damaged or poorly fitted filter frames, seals or gaskets
• •bypass air around the filter bank
• •variations in ductwork layout or damper settings
• •fan or control issues affecting distribution
• •one bank containing a different filter type or condition than the others

If your site uses custom sizes or mixed configurations, it is worth confirming the filter selection and fit with custom air filters or your equipment documentation.

Signs one bank is doing more work than another

You do not always need specialist instruments to notice that a bank is carrying more load. Often the first clues are operational and visual.

Uneven dust loading

When you inspect the banks, one side may look visibly darker, more loaded or more impacted than the others. A bank that is seeing higher airflow will often trap more dust sooner and may show a more pronounced build-up across the media.

Look for:

• •one bank developing resistance faster than the rest
• •more dust on the upstream face of a single bank
• •uneven discolouration across otherwise similar filters
• •a clear difference in condition between banks installed at the same time

Pressure drop differences

If gauges or differential pressure measurements are fitted, compare the readings across each bank where possible. A bank with higher resistance may be more loaded, while a bank with lower resistance than expected may be bypassing air or not sealing properly.

Pressure readings are especially useful when a site has a history of recurring issues. They can show whether the problem is isolated to one bank or part of a wider system imbalance.

Air movement and comfort clues

In some facilities, airflow imbalance shows up through the system rather than the filter itself. You may notice that one zone receives stronger supply air than another, or that airflow at diffusers is less even than expected.

This does not automatically point to the filters alone, but it is a useful clue that the system may not be distributing air evenly across the banks.

Unusual noise or vibration

A bank that is pulling more air than intended can sometimes change the way the system sounds or vibrates. This is not a definitive test, but changes in fan noise, whistling or a new pattern of vibration can justify a closer look.

Why imbalance matters for performance

Airflow imbalance is not just a maintenance curiosity. It can influence how the whole filtration stage behaves.

When one bank does more work than the others, you may see:

• •uneven loading across the installation
• •a shorter useful life for the heavily loaded bank
• •underused filters that do not contribute as expected
• •unstable system resistance over time
• •more frequent corrective maintenance than planned

This can also make it harder to plan filter servicing. If one bank is approaching its loading limit while the others are still relatively clean, you may end up replacing filters in an uneven pattern rather than in a tidy service cycle.

For sites that need to align filtration with ventilation requirements, it is worth checking the broader system against AS 1668.2:2024 and confirming site-specific needs with the mechanical services engineer or building owner.

How to check for imbalance in the field

A practical inspection does not need to be complicated. The aim is to compare like with like and look for differences that point to airflow sharing problems.

Compare similar banks under the same conditions

Check that the banks are the same size, same filter type and similar age. If they are not, the comparison is less meaningful. Mixed media, different efficiencies or different fitments can create resistance differences that are expected rather than faulty.

Inspect seals, frames and seating

A filter that is not seated correctly can allow bypass air and alter how much flow it receives. Check for:

• •gaps around the frame
• •damaged seals or gaskets
• •bent retaining hardware
• •filters that sit unevenly in the housing
• •signs of air leaking around the bank rather than through it

Review dampers and ductwork

If the filter banks feed from common ducting, the issue may sit upstream or downstream. Damper position, duct geometry and restrictions can all affect how air splits between parallel paths.

Use pressure readings where available

When gauges are fitted, note the readings for each bank and compare them over time. A steady change in one bank relative to the others can be more informative than a single reading.

If your site uses a gauge and you are not sure how to interpret it, our guide on how to measure an air filter can help with the basics.

What to do when you find an imbalance

Once you have identified a likely airflow imbalance, the next step is to decide whether the cause is filter-related or system-related.

If the problem appears to be with the filters themselves, you may need to:

• •replace one bank that is significantly more loaded than the others
• •check whether the installed filters match the required specification
• •confirm that all banks were fitted correctly and seated properly
• •review whether the replacement filters are appropriate for the application

If the issue seems to come from the system, the next step may involve a mechanical review of dampers, fans, ductwork or housing design. In that case, your maintenance team or mechanical services engineer should assess the setup before you reset the service plan.

For ongoing support, filter servicing and commercial filter servicing can help keep inspections consistent and documentation organised.

Planning maintenance around uneven loading

When banks do not load evenly, a fixed service assumption can lead to wasted material or missed issues. A better approach is to base maintenance on what the system is actually doing.

That means tracking:

• •pressure drop trends where gauges are installed
• •visual condition of each bank
• •any recurring bypass or sealing issues
• •changes in airflow or system noise
• •whether replacement filters are matching the original fit and resistance

Inspection frequency depends on the system, the site conditions and the dust load. Follow the filter and equipment manufacturer instructions, and use observed condition and pressure drop to guide service decisions.

Some filters are designed to be washable - check the product instructions before cleaning or reusing any product.

If you need to compare options for a difficult installation or a non-standard housing, our our products page can help, and industries we supply shows the types of sites we work with.

Get the right filters for a balanced system

If one bank is working harder than the others, the best fix is not always replacing everything at once. Sometimes the answer is a better fit, a better seal or a filter specification that matches the housing and airflow path more closely.

Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, and we can help you source or make the right filters for your system. Call 07 3800 3448 or request a quote when you need support with standard or custom filter requirements.