Air Handling Unit (AHU) Maintenance Checklist
Keep your AHU running efficiently with structured checks for filters, coils, belts, dampers, and frost protection — built for FM teams managing commercial HVAC plant.
What is an air handling unit (ahu)?
An air handling unit conditions and circulates air as part of a building's heating, ventilation, and air conditioning system. It typically contains filters, heating and cooling coils, fans, dampers, and sometimes humidifiers. AHUs serve large zones or entire floors and are central to maintaining indoor air quality and thermal comfort in commercial buildings.
A typical commercial AHU draws return air from the served space, mixes it with fresh outside air through a mixing box, passes the combined stream through pre-filters and bag/HEPA filters, then through heating and cooling coils, and delivers conditioned air via supply ductwork. Some AHUs include thermal-wheel or plate heat-exchanger recovery to reduce energy use, particularly in modern buildings designed to Part L. Larger plant rooms may run several AHUs in parallel, each serving a separate zone or floor.
From an FM perspective, AHU maintenance — whether you call it air handling unit maintenance, air handling maintenance, or simply servicing the AHU — focuses on three things: air quality (filter condition, coil cleanliness, drain pan hygiene), efficiency (belt condition, bearing health, damper response), and statutory safety (fire and smoke damper interlocks, frost protection). Failures cluster around blocked filters, slipping belts, fouled coils, and seized dampers — most of which are detectable on a structured monthly visual round before they become a fault call.
Typical AHU maintenance checklist
A practical starting point for planned preventive maintenance. Always refer to the manufacturer's O&M manual and site-specific requirements.
Visual Checks
- Inspect pre-filters and bag filters for loading — replace if differential pressure exceeds manufacturer limit
- Check fan belts for tension, wear, and cracking — adjust or replace as needed
- Inspect heating and cooling coils for fouling, fin damage, or corrosion
- Inspect heat recovery wheel or plate exchanger for fouling and bypass damper operation
Functional Checks
- Verify mixing, fresh air, and exhaust dampers operate fully open and closed
- Confirm supply and return air temperatures match BMS setpoints within tolerance
- Check fan bearings for noise, vibration, and temperature
- Test frost protection stat and low-limit controls
- Measure supply and return air pressure to confirm fan operating point
- Verify variable speed drive (VSD) frequency and current at duty point
- Check humidifier operation, demineralised water supply and steam delivery (if fitted)
Cleaning & Housekeeping
- Clean condensate drain pan and confirm drain line and trap are clear
- Clean coil surfaces with appropriate coil cleaner where accessible
- Vacuum or wipe internal AHU casing — including filter housings and mixing box floor
Safety Checks
- Verify fire and smoke damper interlocks function correctly on test signal from fire panel
- Check access panels, interlocks and guards are secure with no exposed rotating parts
Record Keeping
- Record filter differential pressures, fan currents, supply/return air temperatures and VSD speed
- Log belt replacements, filter changes, coil cleans and any component repairs in the asset record
Typical maintenance frequency
Suggested intervals for air handling unit (ahu) maintenance. Actual frequencies should follow manufacturer guidance and site-specific risk assessments.
Monthly
- •Check filter differential pressures
- •Inspect condensate drain pan
- •Visual inspection of fan belts
- •Log fan currents and VSD speed
Quarterly
- •Replace pre-filters if required
- •Check belt tension and alignment
- •Inspect coils for fouling
- •Test damper operation
Every 6 Months
- •Replace bag filters
- •Lubricate fan bearings
- •Full damper stroke test
- •Check frost stat operation
- •Inspect heat recovery components
Annually
- •Full AHU internal inspection
- •Coil deep clean
- •Fan vibration analysis
- •Electrical connection checks
- •Review BMS trending data
- •Statutory fire/smoke damper drop test
Common faults and issues
Issues to be aware of when maintaining air handling unit (ahu) equipment.
Safety and compliance notes
Key safety considerations for air handling unit (ahu) maintenance. This is general guidance only — always follow OEM instructions, statutory requirements, and your organisation's safe systems of work.
Managing AHU documentation with PM Assist
PM Assist helps FM and building operations teams search their O&M manuals and building drawings in seconds. Upload your air handling unit (ahu) documentation and ask questions like “What are the AHU filter specifications?” or “Where is the isolation point for the AHU?” — and get source-cited answers instantly.
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