How to Record Differential Pressure Readings for Audit-Ready Maintenance Logs

Differential pressure readings are only useful if they are recorded in a consistent, traceable way. A clear log helps facility managers and mechanical contractors understand filter condition, spot changes over time and show what was inspected, when it was checked and what action was taken.

This is not about making paperwork for its own sake. It is about creating a maintenance record that is easy to read, easy to hand over and useful when a system needs servicing, troubleshooting or review.

Why differential pressure logs matter

A differential pressure reading shows the resistance across a filter or filtration section. As dust loads build up, pressure drop often changes, which is why recording the reading alongside the date and location gives you more value than a single number on its own.

A good log supports:

• •service history that can be followed by another technician or contractor
• •clearer decision-making when filters are inspected or replaced
• •more reliable handover between shifts, sites or service providers
• •easier reference when comparing current readings with previous checks
• •better alignment with site maintenance procedures and equipment instructions

Where gauges or pressure ports are fitted, monitor the reading and record it in the same format each time. For systems covered by site procedures or ventilation requirements, confirm expectations with the mechanical services engineer or building owner, and consider the relevant requirements in AS 1668.2:2024 where applicable.

What to record every time

The goal is to capture enough detail that someone else can understand the reading without guessing.

Include these details in every entry:

• •Date and time of the reading
• •Site name and specific building, plant room or area
• •System or unit identifier such as AHU number, exhaust unit, terminal device or room number
• •Filter stage or location being measured, for example pre-filter, bag filter bank or final stage
• •Upstream and downstream gauge readings, or the differential pressure value shown by the gauge
• •Unit of measurement if it is not already obvious on the gauge, such as Pa or mmWC
• •Condition notes such as clean, loaded, damaged, noisy or bypass suspected
• •Corrective action taken, if any
• •Name or initials of the person who recorded the reading

If your site has several air handling units or multiple filter banks in one area, include enough location detail to avoid confusion later. A simple tag such as “Level 4 eastern AHU, supply side pre-filter” is much more useful than “unit 3”.

Use the same wording each time

Consistency makes the log easier to review. Choose a standard way to describe the system and keep it the same across all visits.

For example, decide in advance whether your records will always show:

• •building first, then plant room, then unit
• •unit number first, then filter stage, then location
• •gauge reading first, then notes, then action taken

A consistent format is especially useful when several contractors service the same site, or when records need to be checked months later.

A practical log format that works in the field

You do not need a complex system to make audit-ready records. A paper sheet, spreadsheet or maintenance management system can all work if the fields are consistent and the entries are legible.

A simple entry should answer these questions:

• •What was measured?
• •Where was it measured?
• •When was it measured?
• •What was the reading?
• •What did the technician observe?
• •Was any action taken?
• •Who made the entry?

If you use digital records, keep the same naming convention for every site and unit. If you use paper logs, make sure the handwriting is clear and that abbreviations are explained somewhere in the register.

For sites that need replacement or special sizes, it can also help to link the log to the exact filter product used. If you are measuring an existing filter before ordering a replacement, our guide on how to measure an air filter can help reduce guesswork when matching dimensions.

Example of a useful entry structure

A readable record might include:

• •Date: 12 June 2026
• •Site: Northside office building
• •System: AHU-02, level 3 plant room
• •Filter position: pre-filter bank
• •Reading: 145 Pa differential pressure
• •Observation: visible dust loading, seals intact
• •Action: noted for service visit and recheck
• •Recorded by: initials or name

The exact layout is less important than keeping the information complete and consistent.

How to note corrective actions properly

If the reading shows a change that requires attention, the corrective action should be specific. Avoid vague notes such as “checked filter” or “fixed issue” unless you also explain what was done.

Useful corrective action notes might include:

• •inspected filter frame and sealing surfaces
• •cleaned housing or gauge port
• •replaced damaged filter element
• •reseated filter to remove bypass risk
• •checked for dirt build-up around the enclosure
• •escalated to building owner or mechanical services engineer
• •scheduled follow-up inspection after further review

If the filter was replaced, note the product type and size if available. If there was visible damage, include that in the record rather than relying on memory later.

Where a filter is intended to be washed, only follow the product instructions and note that the filter was cleaned according to those instructions. Do not assume all filters are washable.

Common mistakes to avoid in maintenance logs

A log becomes less useful when it leaves too much open to interpretation.

Avoid these common problems:

• •recording only “ok” or “good” without the actual pressure reading
• •leaving out the exact location or unit number
• •using different units of measurement without stating them
• •writing after the fact from memory instead of at the time of inspection
• •failing to note whether the reading was taken before or after a filter change
• •recording an action without stating what changed
• •mixing up several units because the naming system is unclear

It is also worth making sure the log matches the equipment labels on site. If the plant room label says one thing and the maintenance sheet says another, the record becomes harder to trust.

If your site uses different filter classes or standards, keep the product details separate from the pressure record. MERV, EN 779 and ISO 16890 do not convert directly, so it is better to record the exact filter type or product reference than to try to force a comparison that may be misleading.

Making records useful for service history and audits

Audit-ready records are not just tidy documents. They should tell the story of how the system has been maintained over time.

A useful service history usually shows:

• •stable naming for each unit and filter position
• •repeated readings taken in the same way
• •notes that explain any unusual changes
• •evidence of follow-up after an issue is found
• •clear linkage between inspection, action and recheck

If your records are spread across paper forms, emails and job sheets, consider consolidating them into one maintenance register. Even a simple shared file can make it easier to find previous readings when a site manager asks for evidence of servicing.

For larger or more complex systems, commercial filter servicing can help keep records consistent across multiple units and buildings. See our commercial filter servicing and filter servicing pages if you want support with the practical side of keeping systems organised.

Keep the process simple and repeatable

The best logging process is one your team can follow every time. Build a template with the same fields, train everyone to use the same location names and make sure corrective actions are written clearly enough for another person to understand later.

If a reading seems unusual, note it exactly as found and investigate before changing the record. That creates a better history than trying to make every entry look neat. For systems where the filter type, dimensions or housing setup needs attention, our products and custom air filters pages may help with matching the right option to the application.

Need help with filters or service records?

Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, and we work with facility managers and contractors who need practical support with filter supply and servicing.

If you need help selecting the right filters, planning a service or improving your maintenance records, call 07 3800 3448 or request a quote. You can also contact us or explore the industries we supply.