2026-09-27 · class-notes, a-plus, comptia, messer, hardware, cooling, fans, heat-sink, thermal-paste, liquid-cooling
Full class notes for A+ Core 1 3.5: fans and airflow, passive cooling, heat sinks, thermal paste and pads, and liquid cooling.
Class notes · Professor Messer A+ Core 1 (220-1201) · Section 3, lesson 5
Quick reference: the short version of this lesson lives in the A+ Core 1 Section 3 resource sheets. This is a tenth lesson under objective 3.5. Heat is the by-product of everything the hardware does, and this lesson covers the ways we move it out: fans, passive cooling, heat sinks, thermal interface materials and liquid cooling.
By the end of these notes you should be able to:
Everything inside a computer generates heat, and the simplest way to remove it is to pull cool air through the case with fans: cool air comes in one side, passes over the warm components (heating up as it does), and the now-hot air is pushed out the other side.
How well that works depends on airflow, and airflow depends on layout. The arrangement of the motherboard and other components, and how tidily the cables are routed, all affect whether air can travel cleanly from one side of the case to the other. Keep wires and clutter out of the way so air has a clear path. Cases and cooling systems come in many types, and they work together to give the best result.
In the real world: good cable management is a cooling task, not just a tidy one — a mess of cables in the airflow path traps heat.
Look at the adapter cards and you may find some have their own fans, taking cool air from inside the case and directing it onto a hot spot on the card. These need room, so you tend to see them only on larger cards — most commonly high-end video/graphics cards, whose components run very warm.
Fans mounted on the case come in standard sizes — commonly 80 mm, 120 mm and 200 mm. They are often variable speed: slow while the machine is cool, spinning up as it heats. Faster fans are louder, and different makers offer fans with different noise levels — which matters in any environment where you want the machine as quiet as possible.
The surest way to avoid fan noise is to have no fan at all — passive cooling, also called fanless cooling. It suits places that must stay quiet, such as a video server or a set-top box by the television, and purpose-built appliances where the heat is modest and easily managed. Passive cooling is usually paired with a heat sink to take the heat from a component and spread it over a much larger area.
A heat sink is critical for dissipating heat, and a machine may contain several. It works by taking the heat off a component and spreading it across many fins, greatly increasing the surface area available for cooling. As air passes through the fins it picks up the heat and carries it away, and the cycle repeats.
Caution: heat sinks get very hot. If a system has been running, it is easy to burn yourself on one — let it cool before handling.
A heat sink only works well with a good thermal connection to the component beneath it, and that is the job of a thermal interface material.
Thermal paste — also called thermal grease or conductive grease — creates the thermal connection between a hot component and the heat sink. You need surprisingly little: a pea-sized blob is usually enough, because the pressure of the heat sink flattens it and spreads it evenly across the component. Thermal paste is not reusable — remove the heat sink and you replace the paste.
Correction: the transcript calls thermal paste "an adhesive" that lets you "fasten the heat sink". That is imprecise. Thermal paste is a thermal interface material that fills the microscopic gaps between component and heat sink to conduct heat; it does not glue or mechanically fasten the heat sink — that is done by clips, brackets or mounting hardware. (A separate product, thermal adhesive, does bond, but ordinary paste is not glue.)
Note (beyond this lesson): most thermal paste is electrically non-conductive, so a little squeeze-out is harmless. The exception is liquid-metal paste, which is electrically conductive and can short nearby components if it spills — apply it with extra care.
A thermal pad is an alternative you place on top of the hot component before the heat sink. You would choose a pad when you are worried about paste leaking out and damaging other components — pads are less messy to fit. They are not quite as effective as paste, but still make a good connection, and like paste they are not reusable — replace the pad when you refit the heat sink.
Putting it together for a CPU, the layers stack from the hot component upward:
CPU cooling stack (bottom to top):
+-----------------------+
| Fan | moves air through the fins
+-----------------------+
| Heat sink | fins spread heat; air carries it off
+-----------------------+
| Thermal paste / pad | fills gaps -> good thermal contact
+-----------------------+
| CPU | the hot component
+-----------------------+
The CPU is on the bottom; thermal paste or a thermal pad goes on top of it; the heat sink sits on that; and a fan can go on top of the heat sink to push plenty of air down through it. If you need a larger fan, you can mount it sideways — the CPU underneath, the heat sink on top of it, and a big fan blowing air through the whole heat sink.
When fans are too loud or cannot cool enough, the next step is liquid cooling — the same idea used in a car's engine or in mainframes. It is typical on high-end systems, but is now common on home gaming machines and when overclocking a processor for maximum performance.
A liquid cooling system has a block (a heat sink) sitting on the processor, with pipes carrying coolant to a radiator that usually has fans blowing through it. Heat moves from the CPU into the coolant, the coolant flows to the radiator, the fans cool the coolant with air, and the cooled coolant returns to the CPU — a continuous loop.
Liquid cooling loop:
+-------------+ warm coolant +----------------------+
| CPU block | -------------> | Radiator + fans |
| (on the CPU)| <------------- | (air cools coolant) |
+-------------+ cool coolant +----------------------+
^ |
+------------ pump / pipes ---------+
Note (beyond this lesson): the block on the CPU is often called a water block or cold plate. Most home kits are AIO (all-in-one) sealed units — block, pump, pipes and radiator pre-assembled — as opposed to a custom loop you build and fill yourself.
Three machines, three cooling choices.
The pattern: size the cooling to the heat and the noise budget — passive for cool and silent, air for the middle, liquid for hot or overclocked.
Cooling rarely appears in a security lesson, but it maps onto availability and a couple of surprising channels:
| Term | Meaning |
|---|---|
| Airflow | The path of cool air in and hot air out of a case. |
| Case fan | A fan on the case; common sizes 80/120/200 mm. |
| Variable speed | A fan that speeds up as the system heats. |
| Card fan | A fan on an adapter card (often a high-end GPU). |
| Passive cooling | Fanless cooling, usually with a heat sink. |
| Heat sink | Finned metal that spreads heat to increase surface area. |
| Fin | A thin blade of a heat sink that air passes through. |
| Thermal interface material | Paste or pad conducting heat to the heat sink. |
| Thermal paste | Grease filling gaps for heat transfer; pea-sized, single-use. |
| Thermal pad | A solid pad alternative to paste; cleaner, single-use. |
| Thermal adhesive | A separate bonding product (unlike ordinary paste). |
| Liquid cooling | Coolant loop moving heat from a CPU block to a radiator. |
| Water block / cold plate | The block on the CPU in a liquid loop (beyond this lesson). |
| Radiator | Where fans cool the coolant in a liquid loop. |
| Overclocking | Running a CPU faster than rated; needs strong cooling. |
| Thermal throttling | A CPU slowing itself to avoid overheating. |