HVAC Symbols and Meanings (50+ Symbols Explained)

HVAC drawings, schematics and single line diagrams contain a lot of symbols. These symbols represent the devices, equipment and components used in the HVAC system. Beginners often struggle to understand what these symbols mean. So, I made a table to explain the meaning of these common HVAC symbols.

Duct, Grille and Damper

In an HVAC layout drawing, most of the symbols are surrounding ductwork and the related components. So, I start off with these symbols and here are the symbol look and the explanation:

Symbols	Name	Description
	Volume Control Damper	The symbol for Volume Control Damper is a dot and a diagonal line within a rectangular box. The volume control damper symbol can be found on the duct layout drawings and system schematics. The abbreviation “VCD” underneath the symbol indicates the damper is used for volume control.
	Fire Damper	The symbol for fire damper is a dot and a diagonal line within a rectangular box. The fire damper symbol can be found on the duct layout drawings and system schematics. The abbreviate “FD” underneath the symbol indicates the damper is fire-rated. The type of fire damper with such a symbol is usually fusible link.
	Motorized Fire Damper	The symbol for motorized fire damper is a dot and a straight line within a rectangular box. The motorized fire damper symbol can be found on the duct layout drawings and system schematics. The abbreviate “MFD” attached to the symbol indicates the fire damper is controlled by a motor, better known as an actuator.
	Motorized Fire and Smoke Damper	The symbol for motorized fire and smoke damper is a dot and a straight line within a rectangular box. The motorized fire and smoke damper symbol can be found on the duct layout drawings and system schematics. The abbreviate “MFSD” attached to the symbol indicates the motorized damper is not only fire-rated, but also low-leakage to prevent smoke from passing through.
	Non-Return Damper (Backdraft Damper)	The symbol for non-return damper or backdraft damper is a dot and a diagonal line within a rectangular box. The non-return damper symbol can be found on the duct layout drawings and system schematics. The abbreviation “NRD” underneath the symbol indicates the damper is used to prevent airflow from flowing in the opposite direction.
	Linear Diffuser (1-Slot)	The symbol for linear diffuser is a rectangular within a rectangular box. The linear diffuser symbol can be found in the layout drawings. A single internal rectangular box means the linear diffuser is a single slot type.
	Linear Diffuser (2-Slot)	The symbol for linear diffuser is a rectangular within a rectangular box. The linear diffuser symbol can be found in the layout drawings. Two internal rectangular boxes means the linear diffuser a 2-slot type.
	Linear Diffuser (3-Slot)	The symbol for linear diffuser is a rectangular within a rectangular box. The linear diffuser symbol can be found in the layout drawings. Three internal rectangular boxes means the linear diffuser a 3-slot type.
	Linear Diffuser (Side Throw)	The symbol for linear diffusers that are positioned for side throw is two rectangular boxes back-to-back with a smaller box indicating the duct collar. This symbol can be found in the layout drawings. It indicates the supply air will be coming from the wall instead of dropping from the ceiling.
	4-Way Ceiling Diffuser	The symbol for 4-way ceiling diffuser is a square box with 4 arrows pointing at north, south, east and west directions. The 4-way ceiling diffuser symbol can be found in the layout drawings. The arrows indicate the supply air direction. If there are only 2 arrows, it means the supply air blows on two sides only.
	Return / Exhaust Grille	The symbol for return or exhaust grille is a square box with a diagonal line. The return/exhaust grille symbol can be found on the layout drawings. It represents any type of grilles that used for return or exhaust air.
	Round Diffuser	The symbol for round diffuser is a circle with 4 arrows pointing at north, south, east and west directions. The round diffuser symbol can be found in the layout drawings. The arrows are often indicative as round diffusers supply air in all directions.
	Supply Air Duct	The symbol for supply air duct is two lines with the word SAD. If the word is RAD, it means return air duct. If the word is EAD, it means exhaust air duct. If the word is FAD or OAD, it means fresh air duct or outdoor air duct. By default, air conditioning ducts are insulated and toilet exhaust ducts are not insulated even though the symbol doesn’t indicate but the drawing notes do.
	Duct Transition (Reducer / Enlarger)	The symbol for duct reducer and enlarger (transition) is a pair of sloped lines connecting two ducts. Sometimes, the lines are not sloped. This means the duct size changes is on the height instead of the width. This changes can be viewed more clearly on the section/side view drawings.
	45° Entry Branch Duct	The symbol for 45° entry branch duct is a slope before the branch duct. The 45° entry symbol can be found in the duct layout drawings. It indicates the branch duct requires a 45° entry fitting to reduce pressure loss.
	90° Duct Elbow	The symbol for duct elbow is a pair of curved lines connecting two ducts. The angle of the curve is 90° and hence, the elbow is a 90° elbow.
	45° Duct Elbow	The symbol for duct elbow is a pair of curved lines connecting two ducts. The angle of the curve is 45° and hence, the elbow is a 45° elbow.
	Guide / Turning Vanes	The symbol for guide or turning vanes within a duct elbow is multiple internal curve lines. The guide/turning vanes symbol can be found in the duct layout drawings. The number of curved lines indicate the number of guide vanes in the duct elbow. Guide vanes help the air to turn better and reduce pressure loss.
	Duct Internal Insulation (Duct Liner)	The symbol for duct internal insulation or duct liner is a pair of dotted lines on the inside of the duct. The duct liner symbol can be found in the duct layout drawings. It often stretch a few meters from the AHU/FCU for noise suppression.
	Duct Collar	The symbol for duct collar is a small box protrudes out of the duct. The duct collar symbol can be found in the duct layout drawings. It indicates the location where a flexible duct is tapped off the branch duct.
	Duct Canvas (Flexible Connector)	The symbol for duct canvas is a flexible connector between two ducts. The duct canvas symbol can be found in the detail connection drawings of a fan. Duct canvas is used to prevent vibration from propagating from the fan to the duct as large fans move a lot during startup.
	Flexible Duct	The symbol for flexible duct is a cylindrical shape that bends and twists. The flexible duct symbol can be found in the duct layout drawings. The bending and twisting of the symbol is indicative only. In practice, flexible ducts must always be fully extended and installed as straight as possible to reduce pressure loss.
	Vane Axial Fan	The symbol for vane axial fan is two triangle shapes pointing toward a rectangular box. The axial fan symbol can be found in the layout and schematic drawings. It resemble the fan motor and fan blades. The vane axial type of fan is often used in the smoke extraction and pressurization system.
	Propeller Fan	The symbol for propeller fan is two fan blades attached to the shaft of a motor. The propeller fan symbol can be found in the layout drawings, especially on the wall of mechanical rooms that required ventilation. Propeller fan is a type of fan that often installed in the wall.
	Thermostat	The symbol for thermostat is a simple circle with the T word. The thermostat symbol can be found in the layout drawings, schematics and equipment detail drawings. It represent the location of thermostats. Additionally, the symbol can also be used as a general indication of any type of temperature sensors.
	Carbon Monoxide (CO) Sensor	The symbol for CO sensor is a simple circle with the CO word. The CO sensor symbol can be found in the layout drawings, often in basement carpark floors. It represent the location of CO sensors that used to trigger ventilation fans.
	Carbon Dioxide (CO2) Sensor	The symbol for CO2 sensor is a simple circle with the CO2 word. The CO2 sensor symbol can be found in the layout drawings and the schematics of fresh air system. It indicates the use of CO2 sensors to control the amount of outdoor air needed for breathing and general ventilation.

Piping, Valve and Pump

In chilled water system, the layout drawings, schematics and detail installation drawings involve many symbols about the piping, valves and pumps. So, here are the symbol look and the explanation:

Symbols	Name	Description
	Pump	The symbol for pump is a triangle within a circle. The pump symbol can be found in the layout drawings, piping schematics and equipment detail drawings when there is an internal pump. The direction of the triangle arrow indicates the water flow direction.
	Gate Valve	The symbol for gate valve is two opposite triangles. The gate valve symbol can be found in the layout drawings and the piping schematic drawings. Sometimes, the same symbol is used to represent any type of valves that can isolate the pipe section (also known as isolation valve).
	Ball / Globe Valve	The symbol for ball or globe valve is two opposite triangles with a circle in the middle. The ball valve symbol can be found in the layout drawings and the piping schematic drawings. The circle resemble the ball mechanism which ball valves used for water flow control.
	Butterfly Valve	The symbol for butterfly valve is two opposite triangles plus a lever. The butterfly valve symbol can be found in the layout drawings and the piping schematic drawings. The lever resemble the butterfly valve handle that used to open/close the valve.
	Check Valve	The symbol for check valve is a horizontal Z shape. The check valve symbol can be found in the piping schematic drawings. It is usually located after a pump. Sometimes, there is an arrow on the center line or above the symbol which indicates the correct water flow direction.
	Motorized Valve	The symbol for motorized valve is two opposite triangles with an extended M word. The motorized valve symbol can be found in the piping schematic drawings. It is usually located before or after an equipment such as a cooling tower. If the middle of the valve has a circle, it indicates that the valve type is ball or globe valve instead of gate or butterfly valve. The M word means the valve is automatically controlled by a motor or an actuator. But, it can also mean the valve is manually operated but motor-aided (large valve), especially when there is a text saying it is motor operated.
	Balancing Valve	The symbol for balancing valve is two opposite triangles with an extended B word. The balancing valve symbol can be found in the piping schematic drawings. It is usually located before an equipment such as AHU/FCU. If the middle of the valve has a circle, it indicates that the valve type is ball or globe valve instead of gate or butterfly valve. The B word means the valve is meant to manually balance the water flowing into the equipment.
	Pressure-Independent Balancing and Control Valve (PIBCV)	The symbol for pressure-independent balancing and control valve (PIBCV) is a motorized valve symbol with an extra symbol underneath that represents the pressure-independent feature. The PIBCV symbol can be found in the piping schematic drawings. It is usually located after an equipment such as AHU and FCU. If PIBCV is present, balancing valve is not required.
	3-Way Valve	The symbol for 3-way valve is three opposite-facing triangles. The 3-way valve symbol can be found in the piping schematic drawings, especially near the AHU/FCU. The three triangles indicate the direction of the pipe connection and thus the water flow direction. The additional pipe connection is usually for bypass purposes.
	Y-Strainer	The symbol for y-strainer is a straight line with an angled line protruded out. The y-strainer symbol can be found in the piping schematic drawings. The symbol resemble the shape of a y-strainer. The protruded line should be inline with the direction of the water flow.
	Flexible Joint	The symbol for flexible joint is a pair of curved lines, resembling the rubber of a flexible joint. The flexible joint symbol can be found in the piping schematic drawings. It is usually located before and after a vibrating equipment such as pump, AHU, FCU and chiller.
	Temperature Gauge	The symbol for temperature gauge is an extended line with the word T within a circle. The temperature gauge symbol can be found in the piping schematic and equipment detail drawings. The symbol resemble the temperature gauge installation. Sometime, there is an extra symbol underneath the T and circle which indicate a thermowell that ease the maintenance work.
	Thermometer	The symbol for thermometer is an extended line with a rectangular box. The thermometer symbol can be found in the piping schematic drawings. It usually located after an equipment such as pump, cooling tower and chiller. The thermometer is a traditional device used to read water temperature. Sometime, there is an extra symbol underneath the symbol which indicate a thermowell that ease the maintenance work.
	Pressure Gauge	The symbol for pressure gauge is an extended line with the word P within a circle. The pressure gauge symbol can be found in the piping schematic and equipment detail drawings. The symbol resemble the pressure gauge installation. If there is a gate valve symbol on the extended line, it indicates a gate valve is needed for isolation and easy maintenance.
	BTU / Energy Meter	The symbol for BTU or energy meter is a rectangular box with the word BTU. The BTU meter symbol can be found in the layout drawings and the piping schematic drawings. It indicates the location of the BTU meter which is a device used to measure energy usage. Sometimes, there are two lines extended out of the symbol. They are temperature sensors which is a part of the BTU meter used to record the temperature differences.
	Flow Switch	The symbol for flow switch is a square box with the word FS. The flow switch symbol can be found in the piping schematics and equipment detail drawings. It indicates the use of a flow switch which is a device to confirm the present of water flow.
	Differential Pressure Sensor / Switch	The symbol for differential pressure sensor (DPS) is the word DPS within a circle. The DPS symbol can be found in the layout drawings and the piping schematic drawings. It indicates the location of the DP sensors which use for variable speed control.

Electrical, Equipment and Component

There are also many unique symbols in electrical single line diagram (control panel drawing), equipment detail connection drawing and some refrigeration component schematics. So, here are the symbol look and the explanation:

Symbols	Name	Description
	Contactor (Normally Open)	The symbol for contactor is two lines with a gap in between. The contactor symbol can be found in the electrical single line diagram of HVAC systems. The gap indicates the contactor is normally open. Meaning, unless there is a signal, power will not flow through this line to energize the equipment after the contactor.
	Contactor (Normally Closed)	The symbol for contactor is two lines with a gap in between. The contactor symbol can be found in the electrical single line diagram of HVAC systems. When there is a slash on the contactor symbol, it means the contactor is normally closed. Meaning, unless there is a signal to open the contact, power will always flow through this line to energize the equipment after the contactor.
	Compressor	The symbol for Compressor is a circle with two converging lines. The compressor symbol can be found in the schematic diagram of chilled water system, internal refrigeration process and others. The converging lines resemble the compression process where volume is reduced.
	Capacitor	The symbol for capacitor is a straight line and a curved line with a gap in between. The capacitor symbol can be found in the electrical single line diagram of HVAC systems that have a capacitor such as a central air conditioner.
	Cooling Coil	The symbol for cooling coil is two lines with a negative sign in the middle. The cooling coil symbol can be found in the detail drawings of air handling units (AHUs). It is located in between the filter and the supply fan.
	Heating Coil	The symbol for heating coil is two lines with a positive sign in the middle. The heating coil symbol can be found in the detail drawings of air handling units (AHUs). It is located in between the filter and the supply fan.
	Controller	The symbol for controller is a square box. The controller symbol can be found in the detail and schematic drawings of HVAC systems. Some controller symbols contain more details such as a display and buttons to further indicate their functions.
	Humidifier	The symbol for cooling coil is a line with two water spraying icons. The humidifier symbol can be found in the detail drawings of air handling units (AHUs). It resemble the humidification process which involves spraying water into the airstream.
	Finned-Tube Heat Exchanger	The symbol for Finned-Tube Heat Exchanger is a stream of bending line crossed by multiple perpendicular lines. The heat exchanger symbol can be found in the refrigeration schematic of air conditioners. It resemble the evaporator and the condenser of typical split air conditioners where the finned-tube heat exchanger is used.
	Air Filter	The symbol for air filter is two lines with several triangular shapes in between. The filter symbol can be found in the detail drawings of air handling units. It often indicates the primary filter. The secondary filter may be indicated by a more complex symbol or differentiated by a text within the symbol.