3D Printer Cooling: Part Fan and Hotend Fan Setup

Proper 3D printer cooling is critical for print quality. Two distinct fans serve very different purposes: the hotend fan keeps the heat break cool to prevent jams, while the part cooling fan solidifies each layer for clean overhangs and bridges. Understanding and optimising both fans dramatically improves your print results.

Why Cooling Matters in 3D Printing

A 3D printer hotend is a precision thermal system. The nozzle must be hot enough to melt filament (200-260°C for PLA/PETG/ABS), while the heat break just a few millimetres above must stay cool enough to keep filament solid. This thermal transition zone is maintained by the hotend fan.

Meanwhile, each deposited layer of plastic needs to solidify before the next layer goes on top. Without part cooling, layers stay soft, causing drooping overhangs, collapsed bridges, and stringing. The part cooling fan accelerates solidification for clean, precise prints.

Hotend Fan: Keeping the Cold Zone Cool

The hotend fan runs at 100% speed all the time whenever the hotend is heated. It blows air over the heat sink/heat break area to maintain the thermal transition zone. Never turn off the hotend fan while the nozzle is hot — heat creep will cause filament to soften too early, leading to clogs.

Typical hotend fans:

• 4010 axial fan (40×40×10mm): Standard on most printers. Available in 12V and 24V.
• 3010 axial fan (30×30×10mm): Used on compact hotends and Raspberry Pi-mounted toolheads.

The hotend fan mounts directly onto the heat sink, blowing air through the fins. Ensure no obstructions and that air flows freely through the heat sink channels.

Part Cooling Fan: Solidifying Layers Fast

The part cooling fan is controlled by the slicer — its speed varies based on layer, material, and feature type:

• PLA: 100% part cooling from layer 2 onwards. PLA loves cooling.
• PETG: 30-50% part cooling. Too much causes layer adhesion problems.
• ABS/ASA: 0% part cooling in an enclosed chamber. Cooling causes warping and layer splitting.
• TPU/Flex: 20-50% depending on overhang requirements.

Common part cooling fans:

• 5015 blower fan (50×15mm): The gold standard. High static pressure pushes air through narrow ducts.
• 4010 blower fan (40×10mm): Compact option for smaller printers.
• Dual 5015 setup: Premium printers use two blower fans for symmetrical cooling from both sides.

Choosing the Right Fan: Axial vs Blower

Axial fans (standard square fans) move high volumes of air at low pressure. Good for: hotend heat sinks, electronics enclosures, and open-air cooling where there is no restriction.

Blower/centrifugal fans generate high static pressure at lower volume. Good for: part cooling through narrow ducts, cooling through dense heat sinks, and any application where air must be pushed through a restriction.

For part cooling, always use a blower fan. An axial fan may look like it blows more air, but that air lacks the pressure to travel through a duct and reach the print nozzle area effectively.

Fan Duct Design and Airflow Direction

The part cooling fan duct directs airflow exactly where it is needed — at the freshly deposited filament just below the nozzle tip. Design considerations:

• 360° coverage: Air should reach the print from all directions, not just one side. Dual-duct or ring-duct designs achieve this.
• Aim at the nozzle tip: Air should hit the filament 1-3mm below the nozzle, not blow directly at the nozzle (which cools it and causes temperature drops).
• Minimise turbulence: Smooth internal surfaces and gradual transitions improve airflow efficiency.

Popular duct designs like the Hero Me, Satsana, and Fang are available as free STL files on Thingiverse and Printables. Print them in PETG for heat resistance.

Wiring and Firmware Configuration

Wiring: The hotend fan connects to the always-on fan header. The part cooling fan connects to the controllable fan header (usually FAN0 or FAN1).

Voltage matching: Ensure your fan voltage matches your board output. Most 3D printer boards output either 12V or 24V on fan headers. Using a 12V fan on a 24V header will burn the fan instantly.

Firmware settings (Marlin):

// Configuration.h
#define FAN_PIN 9           // Part cooling fan pin
#define FAN_KICKSTART_TIME 100  // ms to run at full speed to start
#define FAN_MIN_PWM 30      // Minimum PWM to keep fan spinning

Klipper firmware:

[fan]              # Part cooling fan
pin: PA8
kick_start_time: 0.5
off_below: 0.10

[heater_fan hotend_fan]  # Always-on hotend fan
pin: PA9
heater: extruder
heater_temp: 50.0

Recommended 3D Printer Fans

Troubleshooting Common Cooling Problems

• Heat creep/clogging: Check the hotend fan is running at full speed and properly directed at the heat break. Replace worn fans. Clean dust from heat sink fins.
• Poor overhangs: Increase part cooling fan speed. Check that the duct is not cracked or misaligned. Ensure the fan is actually a blower, not an axial fan.
• First layer adhesion issues: Disable part cooling for the first 1-3 layers in your slicer. Cooling on the first layer prevents proper bed adhesion.
• Fan not starting at low PWM: Increase FAN_KICKSTART_TIME in firmware. Some fans need a higher minimum PWM to start — adjust FAN_MIN_PWM.
• Temperature fluctuations: Part cooling air blowing on the nozzle causes temperature drops. Adjust duct aim or enable PID autotune to compensate.