Reference Guide
Mechanical & HVAC Abbreviations Guide
100+ common mechanical and HVAC abbreviations used on construction drawings
Last updated: February 2026•Reference Guide
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Equipment
AHU
Air Handling Unit
ACU
Air Conditioning Unit
BLR
Boiler
CHL
Chiller
CRAC
Computer Room Air Conditioning
CT
Cooling Tower
CU
Condensing Unit
DOAS
Dedicated Outdoor Air System
EF
Exhaust Fan
ERV
Energy Recovery Ventilator
FCU
Fan Coil Unit
HRU
Heat Recovery Unit
HP
Heat Pump
MAU
Makeup Air Unit
RTU
Rooftop Unit
SF
Supply Fan
UH
Unit Heater
VAV
Variable Air Volume (Box)
VRF
Variable Refrigerant Flow
WSHP
Water Source Heat Pump
Ductwork & Airflow
CFM
Cubic Feet per Minute
EA
Exhaust Air
FPM
Feet per Minute (air velocity)
MA
Mixed Air
OA
Outside Air
RA
Return Air
SA
Supply Air
TA
Transfer Air
FD
Fire Damper
FSD
Fire/Smoke Damper
MD
Manual Damper
MBD
Manual Balancing Damper
VD
Volume Damper
SD
Smoke Damper
CD
Combination Damper
FL
Flexible (duct)
LG
Linear Grille
RD
Round Duct
REG
Register
Piping & Hydronic
CHW
Chilled Water
CHWR
Chilled Water Return
CHWS
Chilled Water Supply
CWR
Condenser Water Return
CWS
Condenser Water Supply
GPM
Gallons per Minute
HWR
Hot Water Return
HWS
Hot Water Supply
PRV
Pressure Reducing Valve
PSI
Pounds per Square Inch
STM
Steam
COND
Condensate
Units & Measurements
BTU
British Thermal Unit
BTUH
BTU per Hour
DB
Dry Bulb (temperature)
EAT
Entering Air Temperature
EWT
Entering Water Temperature
LAT
Leaving Air Temperature
LWT
Leaving Water Temperature
MBH
Thousand BTU per Hour
RH
Relative Humidity
SP
Static Pressure
TON
Ton of Refrigeration (12,000 BTU/hr)
WB
Wet Bulb (temperature)
WC
Water Column (pressure)
WG
Water Gauge (pressure)
Controls & Automation
ATC
Automatic Temperature Control
BAS
Building Automation System
BMS
Building Management System
DDC
Direct Digital Control
VFD
Variable Frequency Drive
T-STAT
Thermostat
H-STAT
Humidistat
P-STAT
Pressure Switch/Stat
CO2
Carbon Dioxide (sensor)
DPT
Differential Pressure Transmitter
Refrigeration
DX
Direct Expansion
EEV
Electronic Expansion Valve
RFL
Refrigerant Liquid Line
RFS
Refrigerant Suction Line
TXV
Thermostatic Expansion Valve
SEER
Seasonal Energy Efficiency Ratio
EER
Energy Efficiency Ratio
COP
Coefficient of Performance
HSPF
Heating Seasonal Performance Factor
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