CPU Cooler

A CPU cooler is a computer component used to dissipate heat generated by the CPU. This is required to prevent thermal throttling (reducing performance due to high temperatures).

Air Coolers

The most common and cheapest (though certainly not worst!) type of CPU coolers are air coolers. An air cooler consists of a metal heatsink with many fin like structures (to increase surface area for heat dissipation) and usually 1 or 2 fans that blow air through the fins, dissipating heat.

Some processors (e.g. Ryzen 3/5/7's, None-K Intel i3/i5/i7's) come shipped with an air cooler, referred to as a stock cooler. Third-party air coolers typically perform better than their stock equivalents.

AIO Water Coolers

All-in-one water coolers, aka closed loops. These are the water coolers most consumers would use and REQUIRE NO MAINTENANCE. These coolers consist of a CPU waterblock (the part that actually touches the CPU and transfers heat into the water) with an integrated pump and pipes connecting the waterblock to the radiator, which creates a large surface area for fans to blow through it and dissipate the heat.

It is a common misconception that these result in lower temperatures than air coolers. In reality, the best air coolers and the best water coolers are roughly on par temperature wise. To achieve very low temperatures with water cooling, one would need to opt for a custom water cooling loop as covered in the next section, however these custom loops are very expensive, require maintenance and are more for enthusiasts rather than consumers.

AIO water coolers have advantages over air coolers in some regards, such as being less bulky and more attractive (subjective), although they tend to cost more.

Custom Water Cooling

The most efficient cooling systems which allow for significantly lower temperatures than air coolers and AIO water coolers, although the cost and maintenance required for a custom loop makes them less than ideal for those without disposable income or the time to maintain them. There are several important parts required to build a custom loop: Water blocks: these are what actually come into contact with components such as the CPU or graphics cards, and transfer heat from the chips into the coolant within the loop. Pipes: these connect the various parts of the loop. Radiators: these create large surface areas which, in combination with fans blowing through them, dissipate heat from the loop. Fans: these direct air through the radiators, dissipating heat from the loop. Pump: this gets coolant flowing within the pump. Reservoir: not strictly necessary, but having extra coolant in the loop does result in lower temperatures and the reservoir makes it easier to clean out the loop or add more coolant.

Thermal Paste

Allows for efficient transfer of heat from the CPU chip to the heat sink. It is best to apply thermal paste as a single small dot on the center of the chip, which will spread itself evenly across the top surface of the chip when the heat sink is installed on top.

FAQ

Should I buy a third-party CPU cooler, or is the stock cooler good enough?

For most consumers the stock cooler is good enough, however if you wish to overclock your CPU you will almost certainly need a third party CPU cooler. Some Ryzen chips do come with decent stock coolers though, so this may not be necessary for those chips.

Should I get a third-party air cooler or AIO water cooler?

Air coolers and AIO water coolers achieve roughly the same temperatures, so the choice is between lower costs, better value (air coolers) and higher costs, better aesthetics (subjective), smaller form factors (AIO water coolers).

Are custom water cooling loops worth it?

Not unless you are an enthusiast with disposable income and the time and knowledge to set one up. The temperatures are indeed lower (assuming you've set your's up correctly) than what you would get with an air cooler or AIO water cooler, but not low enough to justify their cost to most consumers. Unless your PC is already has a top end CPU, graphics card etc. it is usually best to spend your money on upgrading these components first.