Attic Fan Symbol
Definition: The Attic Fan symbol represents an electrically powered ventilation fan installed in an attic, gable, or roof space to exhaust hot air from the building's upper zone, shown in residential wiring diagrams as a fan-blade icon within a circle connected to Hot and Neutral supply lines, consistent with NEC Article 430 motor wiring conventions and ANSI/IEEE 315-1975 motor/fan symbol practices.
Also known as: attic ventilation fan, gable fan, whole-attic fan, roof exhaust fan, power attic ventilator, PAV.
What the Attic Fan symbol means
The Attic Fan symbol in a wiring diagram represents a single-phase AC-powered ventilation fan that exhausts hot air from an attic or roof cavity to the outside, reducing attic temperatures and the associated heat load on the air conditioning system. The symbol indicates a motorised load connected to the building's AC branch circuit, with the Hot line carrying the switched live conductor and the Neutral completing the circuit.
Attic fans appear in residential wiring diagrams alongside their control devices — typically a thermostat, humidistat, or manual switch — that determine when the fan runs. The symbol's Hot and Neutral pins correspond to the two conductors of a standard 120 V AC single-phase supply. Some attic fans include a built-in thermostat that cycles the fan automatically when attic temperature exceeds a setpoint (commonly 90–110°F / 32–43°C).
How to identify the Attic Fan symbol
The Attic Fan symbol is drawn as a circle with two or more fan blades (a propeller or impeller icon) inside, labelled 'ATTIC FAN' or 'A/F'. Two pins extend from the symbol: Hot (top, connected to the supply phase) and Neutral (bottom, connected to the return neutral). The symbol is similar to a ceiling fan or exhaust fan symbol but is specifically associated with attic or gable installation in a wiring diagram. Some representations show the fan circle with curved blade lines and a text annotation indicating the motor power rating (e.g., '120V 3A').
Function in a circuit
The attic fan motor drives a fan blade assembly to move large volumes of air (typically 800–2,500 CFM) from the attic space through a gable vent, ridge vent, or dedicated roof penetration to the exterior. This reduces attic air temperature, slowing heat transfer through the ceiling insulation into the living space below and reducing air conditioning load. The fan runs on a 120 V AC single-phase induction motor (typically 1/10–1/4 HP) controlled by a thermostat, manual switch, or automatic controller. Proper ventilation requires adequate intake area (soffit vents) equal to or greater than the exhaust area to prevent negative pressure and moisture problems.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-06 covers motor and electromechanical device symbols. Fan/blower loads are represented in IEC diagrams as motor symbols (M) with mechanical load annotations. IEC does not define a specific attic fan symbol; residential wiring diagrams in IEC territories use the generic motor symbol. |
|---|---|
| ANSI/IEEE 315 | ANSI/IEEE 315-1975 Section 7 covers motor symbols; fans and ventilators are represented as motor loads. NFPA 70 (NEC) Article 430 governs motor branch circuit wiring for attic fans. No dedicated ANSI symbol exists specifically for attic fans; the fan-in-circle convention is de-facto standard in US residential wiring diagrams. |
| Key difference | IEC uses a generic motor symbol (circle with 'M') for fan loads; US residential wiring diagrams use a fan-blade-in-circle icon. The functional representation is equivalent; the IEC style is more abstract while the US residential style uses a more pictorial fan symbol. |
Terminals / pins
| Pin | Name |
|---|---|
| hot | Hot |
| neutral | Neutral |
Typical values
Operating voltage: 120 V AC (standard US residential); frequency: 60 Hz; motor power: 1/10 HP to 1/4 HP (75–190 W); airflow capacity: 800–2,500 CFM; typical current: 2–5 A; thermostat setpoint: 90–110°F (32–43°C); circuit breaker: 15 A or 20 A branch circuit; wire gauge: 14 AWG (15 A) or 12 AWG (20 A).
Where the Attic Fan symbol is used
- Residential attic ventilation wiring diagrams showing the fan, thermostat, and branch circuit connection
- New construction electrical plans indicating attic fan location and circuit routing from the panel
- Energy efficiency retrofit wiring diagrams where an attic fan is added to reduce air conditioning load
- Gable-end ventilation systems replacing passive gable vents with powered exhaust fans
- Solar-powered attic ventilator circuit diagrams where the fan symbol is connected to a PV panel symbol
- Combination thermostat/humidistat control wiring diagrams for attic moisture management
- Home inspection and documentation drawings showing existing ventilation equipment
Example
In a residential attic wiring diagram, the Attic Fan symbol connects its Hot pin to the switched output of a line-voltage thermostat (set to 100°F), and the thermostat's supply connects to the 15 A breaker circuit. The Neutral pin connects directly to the neutral bar through a white wire. When the attic temperature rises above 100°F, the thermostat closes and power reaches the fan, running until the attic cools to the thermostat's OFF setpoint (typically 10°F below the ON setpoint).
Key facts
- The Attic Fan symbol represents an AC-powered exhaust fan that removes hot air from the attic space to reduce heat buildup and lower air conditioning load in the living space below.
- The symbol has two pins: Hot (top, the switched 120 V line conductor) and Neutral (bottom, the neutral return), representing a standard 120 V AC single-phase motor load connection.
- Attic fans typically move 800–2,500 CFM of air and are powered by 1/10–1/4 HP single-phase induction motors on a 15 A or 20 A branch circuit, wired with 14 AWG or 12 AWG conductors.
- An integral or separate line-voltage thermostat is almost always included in the circuit; the thermostat controls the fan automatically based on attic temperature, typically switching ON at 90–110°F (32–43°C).
- NEC Article 430 governs motor branch circuit protection for attic fans; the circuit must include an overload protection device sized to the motor's nameplate current rating.
- Adequate intake ventilation (soffit area) must equal or exceed the fan's exhaust capacity to prevent negative pressure in the attic that can draw conditioned air from the living space through ceiling penetrations.
- Solar-powered attic ventilators use a small PV panel to power a DC brushless fan motor — their wiring diagrams show the PV panel symbol connected directly to the DC motor symbol without a separate thermostat.
- The attic fan symbol in residential wiring diagrams is similar to the ceiling fan symbol but is distinguished by placement annotation, lack of light kit pins, and the associated thermostat control wiring.
Frequently asked questions
What does the attic fan symbol look like in a wiring diagram?
The attic fan symbol is a circle with two or more fan blade lines inside, representing a propeller or impeller, labelled 'ATTIC FAN' or 'A/F'. Two pins extend from the circle: Hot (top) for the 120 V line conductor and Neutral (bottom) for the return conductor. It is similar to a ceiling fan symbol but associated with attic or gable installation.
What does the attic fan symbol mean in a residential wiring diagram?
The attic fan symbol indicates a powered exhaust fan connected to a 120 V AC branch circuit that ventilates the attic space. It shows the motor load in the wiring diagram and identifies where the Hot and Neutral conductors terminate. The symbol is usually shown with a thermostat or switch in the same circuit.
What circuit size does an attic fan require?
Most residential attic fans require a dedicated 15 A, 120 V AC branch circuit (14 AWG wire), though larger fans may require a 20 A circuit (12 AWG). NEC Article 430 requires the branch circuit to be rated for at least 125% of the motor's full-load current. The overcurrent protection device (circuit breaker) must be sized per NEC 430.52 for the motor type.
How is an attic fan controlled in a wiring diagram?
An attic fan is typically controlled by a line-voltage thermostat wired in series with the fan's Hot pin. The thermostat closes when the attic temperature rises above its ON setpoint (90–110°F typically) and opens when the temperature falls to its OFF setpoint. Some fans include an integral built-in thermostat eliminating the need for an external controller.
What NEC article covers attic fan wiring?
NEC Article 430 (Motors, Motor Circuits, and Controllers) covers the branch circuit wiring, overcurrent protection, and disconnect requirements for attic fan motors. The fan must have a motor-rated disconnect within sight of the motor location per NEC 430.102. The thermostat control wiring (low-voltage or line-voltage) must also comply with NEC Articles 725 or 430 respectively.
What is the difference between an attic fan and a whole-house fan?
An attic fan exhausts hot air from the attic space to the exterior through a gable or roof vent, while a whole-house fan is a large fan installed in the ceiling that pulls cool outside air through open windows into the living space and exhausts it through the attic and gable vents. Whole-house fans typically require larger circuits (240 V or high-current 120 V) and move significantly more air (3,000–10,000 CFM). Both appear as fan symbols in wiring diagrams but with different circuit specifications.
What standard defines the attic fan symbol?
No single standard defines a specific attic fan symbol. US residential wiring diagrams use a de-facto fan-in-circle pictorial convention. Motor wiring is governed by NFPA 70 (NEC) Article 430. ANSI/IEEE 315-1975 covers generic motor symbols. IEC 60617-06 covers motor symbols in IEC-standard wiring diagrams.
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