HVAC Legends and Acronyms

In mechanical and HVAC (Heating, Ventilation & Air Conditioning) drawings, engineers use standard symbols and abbreviations to represent equipment, ducts, diffusers, dampers, and control devices. Understanding these HVAC legends is most important for understanding construction drawings, preparing BOQs, executing site work, or coordinating with consultants.

This guide provides clear definitions of all commonly used HVAC abbreviations, based on real project drawings and industry standards.
“Note: Following HVAC legends and abbreviations may vary depending on project specifications and international standards.

HVAC Equipment Abbreviations

• FCU – Fan Coil Unit
• FAHU – Fresh Air Handling Unit
• SP – Split AC Unit
• CU – Outdoor Condensing Unit
• AHU – Air Handling Unit
• ACCU – Air Cooled Condensing Unit

Exhaust & Ventilation Systems

• T-EXF – Toilet Extract Air Fan
• KEF-EXF – Kitchen Extract Air Fan

Ductwork Legend

• FA – Fresh Air Duct
• TFAD – Treated Fresh Air Supply Duct
• TRAD – Treated Return Air Duct
• SA – Supply Air Duct
• RA – Return Air Duct

Diffusers & Grilles

• SD – Supply Air Diffuser
• RD – Return Air Diffuser
• SLSD – Supply Linear Slot Diffuser
• RLSD – Return Linear Slot Diffuser
• SAG – Supply Air Grill
• RAG – Return Air Grill
• SAR – Supply Air Register
• RAR – Return Air Register
• EAD – Extract Air Diffuser
• EAL – Exhaust Air Gravity Louver

Dampers & Air Control Devices

• BDD – Back Draft Damper
• DG – Door Grill
• EAG – Extract Air Grill
• VD – Volume Control Damper
• NRD – Non-Return Damper
• SMD – Smoke Damper
• FD – Fire Damper
• MD – Motorized Damper
• MSD – Motorized Smoke Damper
• MFD – Motorized Fire Damper
• MSFD – Motorized Smoke & Fire Damper

Controls & Safety Devices

• SA – Sound Attenuator
• S – Smoke Detector
• CO2 – CO₂ Sensor
• T – Thermostat