Deep Pleat vs Standard Pleat in Packaged Rooftop Units

Packaged rooftop units often have a simple brief: fit neatly into a tight cabinet, keep airflow steady, and provide enough filter surface to handle the site’s dust load. That is where the choice between deep pleat and standard pleat becomes more than a catalogue decision. The right construction can affect how well the filter fits, how much media is available for loading, and how easily technicians can access and replace it.

What changes between deep pleat and standard pleat

At a glance, both filter types do the same job: they remove airborne particles from the airstream before air moves through the system. The practical difference is in how much filter media is packed into the frame and how that media is supported.

A standard pleat filter uses pleated media in a slimmer profile. The pleats are closely spaced, which gives a reasonable amount of surface area in a compact frame. This makes standard pleat filters useful where access is limited and the filter slot depth cannot be changed.

A deep pleat filter uses a deeper frame and more media depth. That extra depth allows the pleats to be spaced and supported in a way that can provide more surface area in the same face size. In many rooftop applications, that matters because more surface area can mean the filter can suit a higher air volume or a heavier dust environment without forcing the system into an awkward retrofit.

The construction difference is not just about appearance. It affects:

• •available media area
• •initial airflow resistance
• •how the filter sits in the rail or track
• •how much room is left for access panels, seals and retaining hardware
• •whether the cabinet can close cleanly without distortion

Why space matters in packaged rooftop units

Packaged rooftop units are rarely generous with filter space. The filter bay may be shallow, awkward to reach, or designed around the original equipment manufacturer’s dimensions. In those situations, a filter that looks suitable on paper may still be difficult to install if the depth, framing or access path is wrong.

This is where mechanical contractors need to think beyond face size alone. A filter can match the length and width of the opening but still fail to work well if the frame is too deep for the available cabinet space, if the holding frame is uneven, or if the filter is forced into position and bypass gaps appear around the edges.

A standard pleat is often chosen when:

• •the cabinet depth is limited
• •access is tight and service speed matters
• •the original design only allows a shallow filter section
• •the unit does not have enough room for a deeper frame without modification

A deep pleat is often worth considering when:

• •there is enough clearance to take a deeper frame
• •the system needs more media area in the same face size
• •the rooftop unit sees higher dust loading
• •the owner wants to reduce the likelihood of rapid loading in a small filter bank

If you are measuring an opening for replacement work, how to measure an air filter is a useful starting point before ordering.

Capacity is about more than filter size

When buyers ask for a “higher capacity” filter, they usually mean one that can handle more dust before resistance rises too quickly. In a rooftop plant application, that is influenced by several practical factors, not just the nominal dimensions.

Deep pleat filters can provide more media area in the same face area, which is one reason they are often considered when space is limited but a more robust filter is needed. That added surface area can help distribute the dust load across a larger area of media. The result may be a better fit for demanding HVAC conditions, provided the unit can physically accommodate the frame.

Standard pleat filters remain a sensible choice where the system was designed around them. They are often easier to handle in narrow or shallow cabinets, and for many packaged units they are the most straightforward replacement. But when the application is more demanding, a standard pleat may reach its loaded condition sooner simply because there is less room for media.

For contractors, the right question is not “which is better” in isolation. It is:

• •what depth does the cabinet allow
• •what pressure drop range is acceptable for the system
• •how much dust is present on site
• •how much service access is available
• •whether the holding frame seals properly with the chosen filter

Airflow, pressure drop and practical service life

Filter selection in rooftop equipment should always consider airflow and pressure drop. A filter that fits physically may still be a poor choice if it places too much resistance on the fan or if the system is sensitive to changes in static pressure.

Deep pleat filters are often selected because they can offer more media area, which may help manage pressure drop as the filter loads. That does not mean every deep pleat will outperform every standard pleat. Construction details such as media type, pleat spacing, frame strength and seal design all affect how the filter behaves in service.

A standard pleat may be the better option when the system needs a compact replacement and the site conditions are relatively clean. A deep pleat may be the better option when the unit must keep operating in a harsher rooftop environment and there is enough room to use the deeper format without creating installation problems.

For ongoing maintenance, inspection frequency depends on the system, site conditions and dust load. Follow the filter and equipment manufacturer instructions, and monitor pressure drop where gauges are fitted. If the filter is in a plant room or rooftop unit that is hard to access, that monitoring becomes especially useful because a visual check alone may not tell you how much loading has occurred.

Choosing the right construction for the job

For commercial buyers, the easiest mistake is treating all pleated filters as interchangeable. In rooftop plant, the filter needs to suit the cabinet, the fan, the maintenance access and the operating environment. A smaller or shallower filter that is easy to fit may be practical in one building, while a deeper filter with more media area may be better in another.

A good selection process should include:

• •the exact filter dimensions available in the unit
• •the direction of airflow through the holding frame
• •how the filter is retained and sealed
• •whether the cabinet can accept a deeper profile without modification
• •whether the replacement needs to match the original equipment design or can be improved within the same footprint

If a project has unusual dimensions or a non-standard filter bay, custom air filters may be the most practical answer. That is often the case with older rooftop plant or equipment that has been modified over time.

Some filters are designed to be washable - check the product instructions. For most rooftop applications, though, contractors and building owners should focus on the product that best suits the intended maintenance method and the site’s dust conditions rather than assuming all reusable-looking filters behave the same way.

When standards and system requirements matter

If the rooftop unit is part of a broader ventilation system, the filtration choice may need to be considered alongside the building’s air handling requirements. In Australia, AS 1668.2:2024 is often part of that discussion, but the site requirements should always be confirmed with the mechanical services engineer or building owner.

It is also worth noting that filter rating systems do not convert directly across standards. MERV, EN 779 and ISO 16890 are not interchangeable on a simple one-to-one basis, so the safest approach is to compare the actual product data for the application rather than relying on rough conversions.

Where higher-efficiency filtration is specified, the details become even more important. For example, HEPA filters are defined by EN 1822 performance at the most penetrating particle size, with H13 at greater than or equal to 99.95% and H14 at greater than or equal to 99.995%. That level of filtration is not the same discussion as a typical rooftop pre-filter or panel filter, so the duty and the housing must suit the product.

Getting the right fit for rooftop plant

The best choice between deep pleat and standard pleat usually comes down to space, access and loading conditions. Standard pleat filters are often the neatest fit in shallow cabinets. Deep pleat filters are worth considering when the unit has room for the extra depth and the application needs more media area in the same footprint.

Total Air Filtration is a family-owned air filter manufacturer and supplier based in Hillcrest, Brisbane QLD, established 2009. We can help supply or make the right filters for your rooftop equipment, whether you need an off-the-shelf replacement or a custom solution.

Call 07 3800 3448 or request a quote. You can also explore our products or contact us if you need help matching a filter to a specific rooftop unit.