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AHU Maintenance Checklist: How to Conduct an Audit and Inspection

Benefit from efficient cooling and longer service life of air handling units by using an AHU maintenance checklist. General inspection procedures are a must-know in this industry. With the help of a checklist, you can be reassured that no item is accidentally forgotten.

What Is an AHU Maintenance Checklist?

An AHU maintenance checklist is a document used as a reference when conducting preventive maintenance for air handling units (AHU). It contains a list of specific procedures that need to be regularly and thoroughly conducted by the inspector and maintenance team because it enables the air handling unit to operate efficiently.

An air handling unit has various mechanical components that enable it to play the role of a heat exchanger. The way it works is that a centralized pump pushes cold or hot water through pipes or coils inside the air handling unit. A fan or blower generates pressure which takes air from the conditioned space and then heats or cools it in the AHU. Afterward, it is returned to the conditioned space.

Air handling units are an integral part of centralized air-conditioning systems since it serves as a large heat exchanger between water and air. This is especially true for large commercial establishments that need to condition large volumes of air every day. And the reason for this is that using water as a medium for cooling and heating is more efficient on larger scales.

In this short guide for AHU audit and maintenance, we will reference the AHU maintenance checklist from the U.S. National Renewable Energy Laboratory (NREL).

In this article, the following points are explained:

1. AHU audit general procedures and maintenance

2. Inspecting AHU components for preventative maintenance

3. How a digital AHU checklist can benefit your business

AHU working energy-efficiently with the help of a maintenance checklist

What Is the General Procedure of an AHU Audit?

An AHU audit is a process used to assess the performance and condition of the air handling units. This includes the assessment of housekeeping and if the current AHU maintenance schedule is adequate.

During an AHU audit, there is a general procedure that needs to be done in sequence. The reason for this is that there is certain information that an inspector needs to collect before moving on to the actual testing.

At the start of the AHU audit, the responsible person must first gather information about the air-conditioning system. Experts recommend doing so by getting the mechanical plans, AHU layouts, and AHU specifications.

Then, study these plans and compute the approximate efficiencies of the system and each air handling unit. Afterward, compute the expected airflow rates from the fan and motor specifications. The results of the computation will be compared to the actual values taken from the tests.

After the computation, the next step is to check the Building Maintenance System (BMS) and record the values of the water and air temperatures that appear in the monitoring system. This will also be compared with the actual values taken during testing.

Finally, it is now time to conduct the actual inspection and testing of the air handling units. The tests to be conducted includes:

  • AHU Fault Detection and Diagnostics (FDD) – This includes reading of temperature and flow rate of water and air (both supply and return). It’s also the calculation of actual performances and comparison with the actual results.
  • VDD/VSD Fault Detection and Diagnostics (FDD) – This includes testing the accuracy of the valve and fan controls.

After the inspection and testing, the next step is to conduct the scheduled preventive maintenance.

Building pipework on the outside of a brick wall

How to Inspect Components During an AHU Preventive Maintenance

As previously stated, an air handling unit is composed of various mechanical components. And these components need to be regularly inspected and maintained to ensure that it is working efficiently. In effect, not only does it reach the desired room temperature but also consumes less energy.

Below are some of the principal components that need to be maintained and some procedures mentioned on the NREL AHU maintenance checklist.

Heating/Cooling Coils

The coils are the component where the heat exchange process happens between water and air. It is also very eye-catching during inspections because of its neatly arrayed fins. And this component is usually protected by filters that remove any unwanted material from going into the coil.

During the air handling unit preventive maintenance, check for any issues within the coils like dirt, dents, and signs of corrosion. Also, the maintenance crew should clean the filters and check for any signs of damage, such as tears and holes. If left dirty, it will cause a decreased cooling/heating efficiency and increased power consumption.

If the coils and filters are consistently getting dirty despite a regular AHU maintenance schedule, it may indicate that there is a need to increase the maintenance frequency. It is also good to consider adjusting the maintenance schedule if there are any nearby sources of dust and debris, such as construction projects.


As previously mentioned, fans and blowers are the moving components of an air handling unit that generate enough pressure to circulate the air between the conditioned space and the air handling unit.

According to the NREL air handling unit preventive maintenance checklist, observe any unusual noises, burnt smells, or excessive vibrations. An unusual noise can indicate that there are loose belts or metal components that are striking each other. A burnt smell can show that motor windings have a problem or that the belt is heating due to friction. Excessive vibrations can indicate that the fan is misaligned.


A damper is an AHU component that is used to control the introduced fresh air, released exhaust air, and recirculated air of the air-conditioning system.

According to the NREL air handling unit preventive maintenance checklist, it is essential to assess if all the dampers are working correctly. To do so, cooperation between the BMS operator and the inspector is needed to check if the damper modulates according to the command given.


An economizer is a system that introduces outside air to the system if the outside air temperature is lower than the return air and if the relative humidity is ideal. This equipment uses temperature and humidity sensors to assess outside air.

According to the NREL AHU maintenance checklist, the inspection is very similar to the damper inspection, where the inspector will check if it is modulating properly. But inspecting an economizer also involves testing the sensors to see if it’s working properly.

Valves and Ducts

Valves are moving components that control the flow of water and air into the cooling coil. These are usually controlled and monitored on BMS or Building Maintenance Systems, so it also needs the cooperation of the BMS operator to check if the valves are modulating properly.

Ducts are metal conduits that serve as air passageways and are connected to the AHU. Because leaks greatly reduce the cooling/heating efficiency of the system, it is important to check if the connection between the AHU and the ducts has leaks during an AHU inspection.

The Benefits of a Using a Digital AHU Inspection Checklist

To make sure your equipment can withstand the test of time, it’s going to need a little polish here and a little oil there every now and then. This is otherwise known as scheduled maintenance. Usually, people think of maintenance as a preventative measure to safeguard against anticipated breakdowns. However, if maintenance is done incorrectly or by an untrained individual, it can end up doing more harm than good. The help of a reliable checklist can prevent expensive machine downtime and repairs by reminding mechanics of the right procedures.

What other advantages does Lumiform offer mechanics doing service maintenance on AHU units?

  • Digitize Checklists – With Lumiform’s digital app and software, you can convert paper documents into digital checklists at the click of a button.
  • Faster CommunicationWith the super intuitive mobile app , you can instantly communicate with your team and alert them to any new maintenance checks and inspections.
  • In addition, we offer more than 10,000 read-made templates for you to adapt and improve to help you get started.
  • All results, images, and comments are automatically bundled into a digital report.This saves you time on post-analysis.
  • You can perform AHU inspections up to 4X faster with a digital checklist than with an old-fashioned pen and paper.

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Inside an air handling unit's red hot heating coils
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