Case fans are the fans mounted on a computer chassis that move air through the case to remove the heat components generate. Airflow fans move a large volume of air through open space, and static-pressure fans force air through resistance such as radiators and dust filters. Setup matters as much as the fan type: intake fans at the front and bottom pull cool air in, exhaust fans at the rear and top push warm air out, and the balance between the two sets the case pressure. This article explains both fan types, the common sizes, PWM and DC speed control, CFM and static-pressure ratings, bearings, and the placement setup that keeps temperatures and dust low.
What Are Case Fans?
Case fans are fans mounted on a computer case that move air through the chassis to carry heat away from the components. Angled blades mount on the front, top, rear, or bottom to draw cool air in or expel warm air out.
The job of a case fan is to create the airflow that feeds the CPU cooler and GPU cool air and removes their heat. Most measure 120 mm or 140 mm across and connect to the motherboard or a fan controller. Case fans differ from CPU-cooler and GPU fans, which mount on the heatsink and the card itself, though all three share the same blade-and-bearing design. The number of case fans and their placement set how much cool air the CPU cooler receives, so case fans directly affect temperatures.
Airflow fans
Static-pressure fans
120 mm
140 mm
What Is the Difference Between Airflow and Static Pressure Fans?
Airflow and static-pressure fans differ in whether the fan moves a large volume of air through open space or forces air through resistance. An airflow (high-CFM) fan uses widely spaced blades for open positions; a static-pressure fan uses tight, often ring-linked blades to push through radiators, fins, and filters:
| Dimension | Airflow Fan (High CFM) | Static-Pressure Fan |
|---|---|---|
| Blade design | Widely spaced, swept blades | Closely spaced, often ring-linked blades |
| Strength | High air volume, low resistance | High pressure through dense obstacles |
| Best position | Open intake and rear exhaust | Radiators, heatsinks, dust filters |
| CFM rating | Higher airflow figure | Lower airflow, higher pressure |
| Static pressure | Lower mm H2O | Higher mm H2O |
| Typical use | Unobstructed case airflow | AIO radiators and filtered intakes |
Use static-pressure fans on radiators and filtered intakes, and airflow fans in open exhaust positions. Many modern fans handle both jobs. Arctic’s specification sheet rates the P12 PWM PST at 56.3 CFM and 2.2 mm H2O of static pressure across a 200 to 1,800 RPM range, so one budget fan covers radiator duty and case airflow alike. The choice still ties to the cooling method.
What Sizes Do Case Fans Come In?
Case fans come in several sizes, with 120 mm and 140 mm the most common; larger fans move more air at lower noise.
The 120 mm size fits the widest range of case mounts and radiators. A 140 mm fan moves more air per rotation, so the 140 mm fan spins slower, and therefore quieter, for the same volume: a 140 mm fan at 1,000 RPM roughly matches a 120 mm fan at 1,400 RPM with less noise. Sizes of 80 mm, 92 mm, and 200 mm exist for specific cases. Typical case fans run from about 500 RPM at idle up to 2,000 RPM under load.
What Is the Difference Between PWM and DC Fan Control?
PWM and DC control differ in whether the fan speed is set by a pulsed signal or by varying the supply voltage:
A PWM fan uses a 4-pin connector with a control pin that switches power on and off rapidly. The pulsed signal sets speed precisely without changing voltage, holds a steady low minimum, and follows a temperature-based fan curve. A DC fan uses a 3-pin connector and varies the supply voltage from 12 V down to about 5 V. Control is coarser, and the fan stalls if the voltage drops too low. Either way, a 3-pin DC fan still runs on a 4-pin PWM header in voltage mode.
PWM’s lower idle speeds keep the CPU cooler quiet at light load and ramp up only under heat. Our recommendation is to buy 4-pin PWM fans for any new build and tie the fan curve to the CPU and system temperature.
How Do CFM and Static Pressure Ratings Work?
CFM and static-pressure ratings state how much air a fan moves and how forcefully it pushes against resistance:
CFM, cubic feet per minute, measures the open-air volume a fan moves, so higher CFM cools better in an unobstructed position. Static pressure, stated in millimetres of water (mm H2O), measures the force the fan builds against resistance, and higher pressure pushes air through radiators and filters. The two ratings trade off: a high-CFM design gives up static pressure and vice versa. A radiator needs roughly 2 to 3 mm of water to perform.
Manufacturers publish both figures. Noctua’s datasheet rates the NF-A12x25 at 60.1 CFM and 2.34 mm H2O at its 2,000 RPM maximum, so one fan works in radiator and open positions alike. Noctua introduced the second-generation NF-A12x25 G2 in June 2025 with a 1,800 RPM ceiling, and as of 2026 both generations remain in Noctua’s lineup, with the Cybenetics test lab grading the G2 Platinum for airflow and Titanium for static pressure.
How Do Intake and Exhaust Set Case Pressure?
Intake and exhaust fans set case pressure by balancing how much air enters against how much leaves, creating positive, negative, or neutral pressure. Intakes (front, bottom) draw cool air in; exhausts (rear, top) push warm air out:
- Positive pressure moves more air in than out, so air exits through every gap and dust enters only through filtered intakes, which keeps the interior cleaner.
- Negative pressure moves more air out than in, which improves heat removal but pulls unfiltered dust through every case gap and crack.
- Neutral pressure balances intake and exhaust equally, which suits most builds when intake fans use dust filters.
Most builders run slight positive pressure with filtered intakes to cut dust while keeping strong airflow through the case.
What Are the Types of Fan Bearings?
Fan bearings come in four main types – sleeve, ball, fluid-dynamic, and magnetic – differing in lifespan and noise:
- Sleeve bearings use a lubricated shaft, run quietly when new, and last around 30,000 hours, but wear faster when mounted horizontally.
- Ball bearings use steel balls, last 50,000 to 75,000 hours, and tolerate any mounting orientation and high temperatures, with slightly more noise.
- Fluid-dynamic bearings use a pressurized oil film, run quietly, and last 100,000 hours or more, which suits premium fans.
- Magnetic-levitation bearings suspend the hub on a magnetic field, nearly eliminate friction, and last the longest at the highest cost.
Noctua rates the SSO2 self-stabilizing oil-pressure bearing in the NF-A12x25 at a mean time to failure above 150,000 hours and backs the fan with a 6-year warranty, while budget fans rely on sleeve bearings. The bearing type sets both the lifespan and the noise a fan develops over years of use.
What Is the Best Case Fan Placement Strategy?
The best strategy is front and bottom intake, rear and top exhaust – cool air enters low and front, crosses the graphics card and CPU cooler, and exits up and back with the natural rise of warm air:
A typical layout runs two or three front intake fans and one rear exhaust fan, plus top exhaust where a radiator or vents allow. The theCoreiTech team recommends static-pressure fans with dust filters on the intakes and a high-airflow fan in the open rear position. Align the case intake direction with the CPU cooler fan so both move air the same way. A radiator mounts as front intake for the coolest air, or as top exhaust to expel the radiator’s heat directly.
Good placement supports lowering CPU temperature more than raising fan speed alone.
Which fan type goes where
| Position | Best fan type | Why |
|---|---|---|
| Case intake / exhaust (open vents) | High airflow (CFM) | Moves large volumes of air through open space. |
| Radiators and dense heatsinks | High static pressure | Pushes air through tight fins against resistance. |
| Restricted or mesh-blocked panels | Static pressure | Keeps airflow strong against the restriction. |
Last Thoughts on Case Fans
Case fans set the airflow that carries heat away from every component, so the fan type, size, control, and placement decide how cool a build runs. Airflow fans move high volume through open positions, static-pressure fans force air through radiators and filters, and 140 mm fans run quieter than 120 mm fans at the same airflow.
Key Takeaways:
- Case fans move air through the chassis to supply cool air to the components and expel the heat they generate.
- Airflow fans move high volume through open space, while static-pressure fans force air through radiators, heatsinks, and filters.
- 140 mm fans move more air at lower noise than 120 mm fans, because the larger blade spins slower for the same airflow.
- PWM 4-pin control sets speed precisely through a pulsed signal, while DC 3-pin control varies voltage with coarser low-speed control.
- Positive pressure with filtered intakes reduces dust, and front-intake, rear-and-top-exhaust placement directs cool air across hot parts.
Frequently Asked Questions (FAQs)
What is the difference between airflow and static pressure fans?
Airflow fans move a high volume of air through open space, while static-pressure fans force air through resistance such as radiators, heatsink fins, and dust filters.
Are 140mm fans better than 120mm fans?
A 140 mm fan moves more air per rotation, so it spins slower than a 120 mm fan for the same airflow, which lowers noise. The 120 mm size fits more mounts.
What is the difference between PWM and DC fans?
PWM fans use a 4-pin connector and a pulsed signal for precise speed control. DC fans use a 3-pin connector and vary voltage, offering coarser control that cannot run as slow.
Should a PC have positive or negative pressure?
Positive pressure is generally better. Moving more air in than out with filtered intakes forces air out through gaps, so dust enters only through filters, keeping the interior cleaner.
How many case fans do I need?
Most builds use two or three intake fans at the front and one exhaust fan at the rear, adding top exhaust fans where vents or a radiator allow.
What is CFM on a case fan?
CFM, cubic feet per minute, measures the air volume a fan moves in open air. A higher CFM fan supplies more cooling air in an unobstructed case position.
