How to Specify Replacement Filters for Rooftop Units on Logistics Warehouses

Rooftop packaged units on logistics warehouses work hard in tough conditions. Wind-blown dust, heat, rooftop access limits and weather exposure can all affect how well a replacement filter fits and performs, so the right order starts with careful checking rather than guessing.

For mechanical contractors and facility managers, the key is to confirm the filter dimensions, construction, air flow requirements and how the unit is actually installed on site. A few minutes spent checking these details can save a lot of back-and-forth when ordering replacements.

Start with the unit details, not just the old filter

The first step is to identify the air handling unit correctly. Roof-mounted packaged units are often similar from the ground, but the filter arrangement can vary between models and even between production runs.

Check the unit nameplate and record:

• •Manufacturer and model number
• •Serial number if available
• •Filter bank location and access side
• •Number of filters fitted
• •Any notes on the door, frame or service panel

If the old filter is missing, damaged or crushed, the unit details become even more important. They help you match the correct size, thickness, media type and frame style before you place an order.

If you are unsure how to take the measurements properly, our how to measure an air filter guide is a useful starting point.

Measure the filter correctly

A replacement filter should be specified from the actual filter opening or the existing filter dimensions, not from a rough estimate. Small differences can cause bypass, frame damage or poor sealing.

Measure:

• •Length
• •Width
• •Depth or thickness
• •Any lip, flange or gasket dimensions
• •The inside dimensions of the filter rack if the old filter is missing

Measure in millimetres and check the size in more than one place. On older rooftop units, the frame may not be perfectly square, and the opening may have shifted over time. If the filter is a panel style, measure the media face and the overall frame, not just one visible edge.

Also confirm the direction of airflow. Some filters are designed to be installed in a specific orientation, and the arrow on the frame or label must match the unit airflow.

If the dimensions are non-standard, ask about custom air filters rather than forcing a close enough size. A custom-made filter is often the better option when the frame is unusual or the unit has been modified.

Check the frame, seal and access arrangement

On rooftop units, fitment issues are often caused by the frame and seal rather than the media itself. High wind exposure can work loose any weak points, and rooftop heat can affect gaskets, clips and retaining hardware over time.

Before ordering, check:

• •Whether the filter uses a cardboard, metal or synthetic frame
• •If a gasket or foam seal is fitted
• •Whether the filter slides into rails, clips into a holding frame or drops into a cassette
• •Whether access is from the side, top or end
• •Whether the door clearance allows the filter to be inserted without bending

A filter that is technically the right size can still be a poor choice if the frame does not suit the holding method. For example, a rigid filter may not fit where a flexible panel was originally used, and a thick filter may foul the access door.

If the existing filter seal is compressed, split or missing, replace the seal arrangement at the same time if the unit design allows it. For rooftop units exposed to wind, that detail matters as much as the media grade.

Match the filter type to the site conditions

Logistics warehouses often sit in exposed industrial areas where rooftop units draw in external dust, road grime and airborne debris. That means the filter selection should suit the site, not just the equipment label.

Consider:

• •The type of dust around the site
• •Whether nearby loading docks, roads or yards increase particulate load
• •How much outdoor air the system introduces
• •Whether the unit serves general warehouse areas, offices or both
• •Whether the system has pre-filtration stages already fitted

If the system uses a staged arrangement, confirm whether you are replacing the primary panel, a deeper pleated filter, or both. Mixing the wrong filter types can affect fit and maintenance access.

Filter ratings do not convert directly between MERV, EN 779 and ISO 16890, so avoid guessing based on an old label from another system. If the project documents call up G3, G4 or F5-F9 classes, remember those are EN 779 classes that are still widely used in Australia, even though ISO 16890 is now the current standard framework.

For new installations or upgrades, site requirements should be confirmed with the mechanical services engineer or building owner, particularly where AS 1668.2:2024 applies to the ventilation system design.

Confirm pressure drop and airflow requirements

Rooftop units can lose performance if the replacement filter is too restrictive or too loose for the system design. That is why airflow and pressure drop should be checked before ordering, especially where gauges or sensors are fitted.

Ask for or record:

• •Rated airflow through the unit
• •Initial pressure drop of the current filter type, if known
• •Final or change-out pressure drop guidance from the equipment documentation
• •Whether the unit has differential pressure gauges or monitoring points

If the existing filter is heavily loaded with dust, the pressure reading may not represent the filter specification accurately. In that case, inspect the whole filter bank and compare the current installation with the unit documentation rather than relying only on the old filter label.

Where pressure drop monitoring is fitted, it is best practice to watch how the filters behave over time and replace them according to the equipment manufacturer instructions and site conditions, rather than on a fixed calendar schedule.

Consider rooftop exposure and maintenance access

Logistics warehouse roofs can be harsh working environments. Heat, UV exposure, wind uplift and difficult access all affect the choice of filter construction and the way it is serviced.

A practical spec should take into account:

• •Whether the filter housing is weather-shielded
• •Whether the access route makes large or fragile filters difficult to handle
• •Whether service staff need quick change-outs
• •Whether the unit is likely to see heavy dust loading during certain site activities

Some filters are designed to be washable - check the product instructions before assuming a filter can be cleaned and reused. If a washable option is being considered, confirm that it suits the system, the maintenance process and the site’s cleaning capability.

If the rooftop unit is serviced by an external contractor, make sure the ordered filter format matches the way the contractor accesses and replaces it. A filter that is awkward to fit can lead to damage, leakage or longer downtime.

What to have ready when you place the order

Before you order, gather the key details into one note or service record. This helps avoid mistakes and makes repeat ordering much easier.

Have ready:

• •Unit make, model and serial number
• •Filter length, width and depth in millimetres
• •Frame material and seal type
• •Airflow direction
• •Number of filters required
• •Any special access or fitting notes
• •Photos of the filter rack, old filter label and unit nameplate

If the site has multiple rooftop units, label each filter set clearly. Warehouses often have similar units across a roof, but a close match is not always an exact match.

Keep records of the installed filter specification for future filter servicing and replacements. That saves time when the next order is needed and helps maintain consistency across the site.

Need the right filter for a rooftop unit?

Total Air Filtration is a family-owned air filter manufacturer and supplier based in Hillcrest, Brisbane QLD, and we can help supply or make the right replacement for rooftop packaged units in demanding industrial sites.

If you need help matching a size, checking a frame style or ordering a non-standard filter, call 07 3800 3448 or request a quote.

You can also view our products, learn about filter servicing, or see the industries we supply.