Why Do CPUs Generate Heat?

All CPUs (Central Processing Units) generate heat. The CPU generates the most heat among all hardware components in personal computers unless you have a more powerful GPU (Graphics Processing Unit). 

CPUs generate heat as they convert electricity into thermal energy. A modern CPU has a few billion transistors or switches regulating the electricity flow throughout the processor, thus causing energy loss and conversion to heat. 

They also generate heat due to higher thermal design power (TDP), turbo boost, hyperthreading or overclocking, and faster bus speeds, among other factors. Also, inefficient cooling and enormous real-time processing demand can overheat CPUs.

Abstract design for CPU heat.

However, the specifications of modern CPUs, how ICs are made, and what they can do will also affect how much heat a computer releases.

Why Do CPUs Generate Heat?

The primary reasons are entropy, thermodynamics, and Joule’s law.

1. Entropy and Thermodynamics

So, let’s look at the science behind a hot CPU in simple terms.

The first law of thermodynamics implies that heat energy can neither be created nor destroyed. All power, such as electricity, kinetic, and mechanical energy, follows this rule. 

Now, the second law of thermodynamics sheds light on entropy. According to this law, heat transfer is inevitable if entropy (energy transfer) is constant in a system with an energy inflow.

In simpler words, a computer must utilize the electricity flowing into the CPU or lose the energy in heat. 

So, as your computer receives power from an electrical outlet or battery, it will generate heat as a healthy way to eliminate any extra energy.  

If there is no heat transfer, a system’s entropy or CPU, in this case, cannot remain constant, and the components will disintegrate.

However, your CPU will not suffer material damage since it can release heat instead of frying itself inside. 

Also, this explains why an overheated CPU that cannot cool down will suffer structural damage and eventually fail. 

2. Joule’s Law

Joule’s law states that resistance in a circuit will convert electricity to heat energy. 

A CPU does not have resistors or the resistance we associate with wires and other objects.

However, a CPU’s integrated circuit (or chipset), comprising the semiconductors, transistors, and diodes, has some resistance that leads to electric energy loss and conversion. 

The only scenario when electricity flows without resistance is when using a superconductor. 

A CPU has semiconductors with a lower conductivity than the efficient superconductors we use in electric circuits or wiring.

Also, the transistors are essentially switches. They allow or block the flow of electricity depending on the input and output requirements, thus creating resistance. 

So, these semiconductors and transistors create heat whenever they don’t use as much electricity as possible. 

3. The specifications of modern CPUs

A computer's CPU.

A CPU performs numerous tasks simultaneously, requiring tons of electric current inputs and outputs through transistors, semiconductors, and gates. 

Also, electric energy powers the computer and its hardware components, including the CPU, thus heating all these parts.

If a CPU cannot transfer the excess heat, it will get super hot.

The most significant reason modern CPUs generate so much heat is their specifications.

A typical CPU used in computers today is exponentially more powerful than the processors of the last century. 

Let me highlight a few key differences that directly impact the heat generated:

Thermal Design Power (TDP)

A CPU like the Intel 8086 released in 1978 consumed 1 W of power. However, a modern CPU like the Intel Core i7-8086K released in 2018 has a thermal design power (TDP) of 95 W. 

There are CPUs with TDPs as high as 380 W. The TDP is not necessarily the real-time power draw.

However, the thermal design power is what a processor can draw and use without overheating. 

Note the quantum leap from 1 W to 95 W, 165 W, 255 W, and 380 W. You can imagine the kind of heat new CPUs generate. 

For perspective, a 100 W incandescent light bulb’s external temperature can be as high as over 250 °F (121 °C). 

Modern CPUs have thermal throttle points at about 194 °F (90 °C) to 212 °F (100 °C) to protect the processor from very high heat.

The number of transistors

The now obsolete Intel 8086 processor had 29,000 transistors. In contrast, modern CPUs like the Intel Core i7-8086K have around 3 billion transistors.

These transistors regulate the flow of electricity through a CPU’s logic gates.

Compare up to 3 billion transistors or switches allowing or blocking electricity flow through an integrated circuit with the primitive 29,000.

That’s a ton more transistors and, thus, more heat!

Frequency/Clock speed (Rate)

The processor frequency or CPU clock speed of the Intel 8086 was 0.005 to 0.001 GHz. This speed increased to 4.0 GHz in the Intel Core i7-8086K, with an additional 1.0 GHz turbo boost.

Thus, a modern CPU can operate at 5.0 GHz when overclocked.

The increasing frequency or speed is essentially computing or processing power, which is directly dependent on the electricity drawn by the CPU, among other hardware components. 

Naturally, the more electricity a CPU draws, the greater its heat generation and transfer. 

CPU Bus Speed

You probably assume all these specifications are correlated and have significantly improved in the past few years.

Therefore, there is a compounding effect on the heat produced by a CPU. 

Take the example of the bus speed. Intel 8086’s bus speed was 4.77 MHz, whereas Intel Core i7-8086K has a whopping 2,966 MHz.

A higher bus speed, like quicker processing or clock rates, draws more power. So, in effect, a faster and more powerful CPU generates more heat. 

Integrated Graphics

You may know that CPUs did not have any onboard graphics for many years since their inception. Today, you will struggle to find a branded CPU without any integrated graphics

A CPU’s integrated graphics usually generate less heat than a GPU. However, it can warm things up, contributing to heat transfer.

Turbo Boost, Hyperthreading, or Overclocking

Most CPUs available have turbo boost, hyperthreading, or overclocking. These features enhance the computing or processing speed of a CPU.

Thus, the processor can breach its TDP and use more electricity if you overclock a CPU or use its turbo boost. In effect, the CPU will generate more heat. 

CPU Size, heatsink, and fan

Last but not least, note the size of a CPU. 

An integrated circuit or chipset measuring 2 inches x 2 inches (5 cm x 5 cm) does not have enough surface area to distribute heat efficiently.

So, most CPUs have a heatsink to radiate heat more efficiently, and a fan will usually be nearby to cool everything off. 

In a well-built computer, the heatsink and fan should transfer the excess heat from the CPU.

However, a dusty heatsink and fan may impair their efficiency and efficacy. Hence, the CPU will have no other option but to overheat.

How much heat do CPUs generate?

Generally, CPUs generate heat of around 104 °F to 122 °F (40 °C to 50 °C) when idle. Based on the real-time processing and computing demands, the average heat produced increases up to 176 °F (80 °C). A stressed and overheated CPU may be as hot as 212 °F (100 °C).

A CPU’s heat output depends on its real-time processing performance and how much load it has to endure to serve your computing needs.

Also, the ambient temperatures significantly influence the temperature–  CPUs cool much faster during winters than in summers.

Furthermore, the cooling effect of the fans in your computer, especially the one on the CPU, will determine how hot the processor is at any given moment. 

In rare cases, a defective mainboard may influence the flow of electricity to various hardware components, such as the CPU fan.

In that case, your CPU fan may be alright, but it won’t properly function if it cannot draw sufficient power.  

Why is my CPU so hot when idle?

Your CPU may be hot when idle if you have demanding programs or applications running in the background. Also, your computer may get hotter if you have a failing heat sink or malfunctioning fan. 

As I’m sure you are aware, computer fan speeds vary based on the required amount of cooling at any given moment.

The fans mounted on the cabinet for a desktop computer run faster when the system is hot and slow down when the hardware components are relatively cool. 

In contrast, the CPU fan operates continuously whenever your computer is on, even when the system is idle.

So, your CPU will be hot when idle if the fan fails or does not run at the ideal rotations per minute.

It is important to check that the cooler is mounted properly to ensure it can do its job.

Overheating will occur quickly if there’s a gap between the CPU cooler’s heatsink contact area and the CPU itself.

How is CPU overheating diagnosed?

CPU overheating is diagnosed with an application. You may try free software like Core Temp, Real Temp, Speed Fan, HWMonitor, HWiNFO, Speccy, CPU Thermometer, Open Hardware Monitor, and AIDA64. Then, detect the cause and fix it to cool it. 

One practical way to diagnose an overheating CPU is by reviewing the activities preceding a temperature spike. 

Suppose your CPU is too hot even when you have closed all non-system processes. In that case, the culprit is probably hardware-related.

The problem usually has something to do with the fan, heatsink, thermal paste, or mainboard. 

Also, you should check for overclocking and customized fan settings.

If you use applications to overclock your CPU and regulate the speeds of other fans, these bespoke changes may lead to overheating or worsen a pre-existing problem.

Be sure to reset the fan speed to the default settings before you go poking around for a hardware issue.

Fixes for common CPU overheating issues

The latest CPUs do not overheat beyond their thermal throttling points.

However, it would be best if you operated a CPU at temperatures much lower than its thermal junction maximum to prevent damage. So, how do you fix an overheating computer and help it cool down?

Here are the common ways to fix an overheating CPU:

  • Clean the CPU’s heatsink and fan.
  • Reapply thermal paste if it is dry or worn out.
  • Check if all the fans are functioning optimally.
  • Ensure there is no obstruction for the fans. 
  • Wipe off dust and dirt from inside the cabinet.
  • Avoid running too many programs simultaneously.
  • Review CPU, hardware, and software compatibility.
  • Do not overclock your CPU if it causes overheating.
  • Use an application to monitor CPU temperatures.
  • Add a fan if you have a vacant slot in the cabinet.

You may have a failing mainboard, but such a hardware issue should affect more components than just the CPU.

Also, you may have a faulty CPU, which is replaceable under warranty.

You must contact a technician or buy a new CPU if the warranty is no longer applicable.

CPUs are among the most reliable hardware components in computers.

However, like all parts, a CPU can fail. If none of these fixes worked, you might need to replace it.

Also, please do not allow it to generate too much heat consistently. Such overheating can damage the CPU, mainboard, and other hardware. 

Please refer to how to check if a CPU is working to establish its proper working order.