Building an energy efficient computer Nov 2009

Updated March, 2010 with video card and TDP information

Updated May 2010 with computer case and air cooling information

Updated July 2010 with Wattage information

Unfortunately, trying to do this is not an easy task. Building an energy efficient computer requires the knowledge of what causes the computer to not be energy efficient.  Furthermore, the parts that are energy efficient do cost more.  In any case I will list the parts that one can buy, and the things one can do that are energy efficient.

NOTE:  When purchasing a CPU, video card, or any component that requires a heatsink, look for the TDP (thermal design power).  TDP is almost always understated, therefore, take this into consideration when looking at the TDP.  Comparing TDP for components from the same manufacturer may provide more accurate results.  Comparing TDP for components from different manufacturers may not.

TDP – The “theoretical” maximum power the component will draw when running real applications.  Therefore, a CPU that is rated for 100W TDP will “theoretically” draw 100W of power running at 100% efficiency.

AMD seems to have removed TDP and simply called it wattage as of July 16, 2010.  As one will see, the CPU’s vary in the amount of electricity that it uses.  AMD CPU’s can consume anywhere from 25W for a 1800MHz CPU to 140W for a 3400MHz CPU.  Usually slower processors use less electricity.

I always replace the stock heatsink/fan with an aftermarket heatsink that will house a 120mm fan.  The smaller fan on the stock heatsink has to spin faster to push the same amount of air on the heatsink than a 120mm fan.  The energy efficiency is debatable, but the 120mm fan does spin slower.

Power supply – Try to get an energy efficient, 80 plus in the Wikipedia at or the official website at, power supply that is double the amount of power that you will use.  A good energy efficient power supply will be most energy efficient when it is loaded at about 50%.  The power supply becomes less efficient as the load increases or decreases from 50%.

For a list of vendors that sell energy efficient power supplies, one can look at

Currently, 400W -> 450W power supplies are what people will see in most household computers.  If one is required to use a 1000W power supply, he/she most likely has a hard-core gaming power hungry machine and/or a server with 10 hard drives installed.

CPU – Oddly enough, if you underclock a CPU, one can make the CPU more energy efficient.  Unfortunately, this requires a lot of fiddling and testing.  A simple Google search for underclock CPU will give lots of results.  It also seems that undervolting actually provides more energy savings, but can make the computer unstable.

Underclocking can be found in the wikipedia at and at

Video card – Depending on which video card that you use, and how graphic intensive the application is, the power consumption of a video card will vary greatly.  Video cards currently max out at over 300W of power.

A comparison of several video cards and their power consumption at

As a general rule, slower graphics cards without fans use less power.  For example, the ATI Radeon™ HD 5450 fanless graphics card, less powerful, uses 6.4 Watts of power when idle.  The ATI Radeon™ HD 5970 graphics card, much more powerful, uses 51 Watts of power when idle.  These numbers were taken from AMD’s website.  Mine, an ATI Radeon 4350 fanless graphics card, supposedly uses 20 Watts of power under a full load.  Remember that graphic card fans require power to operate.  Therefore, graphic card fans will increase the graphics card’s power consumption.

Fans – A fan that spins faster will use more electricity than a fan that spins slower.  Furthermore, avoid fans with LED lights.  They use more electricity since they have to light up.  One will have to do a comparison of the different fans available and see how much watts the fan uses.  A comparison between three fans is given below.

  • 80mm Power consumption 3.12W Max. Air flow 40.8 CFM
  • 120mm fan Power consumption 1.8W + / – 10% Air Flow 44.73CFM
  • 200mm fan Power consumption 3.36 W Air Flow 110 CFM

It is apparent that a larger fan uses less electricity to push the same amount of air, air is measured in CFM and a larger number means more air being pushed, than a smaller fan.  Furthermore, it is also more quieter.  Therefore, a larger fan is more energy efficient.

Unfortunately, there is a limit to the size of fan usable depending on the computer case design.  A large fan may not fit on many computer cases.  120mm case fans are quite common and many cases are designed to use them.  Therefore, when it comes to energy efficiency, 120mm is the best that will fit most cases.

Air cooling -There are many people online that will defend the fact that a computer is better cooled when more air is going into the case than coming out.  Furthermore, there are many people that will argue that a computer is better cooled when more air is coming out than going in.  An article that talks about this in detail can be found at  I think that negative air pressure is better, but it requires more dusting.

As for being more energy efficient, variable speed fans have to work harder and suck more electricity to keep the inside cool.  Therefore, one will have to decide on either negative or positive air pressure.

Hard drive – Strangely enough I have seen some.  If you visit, they sell both low power and regular hard drives.  Typing in low power in Seagate’s search box will give numerous results.  I have not done much research on this yet.  I wonder if this is just a sales pitch?  Seagate’s low power hard drives can be seen at

Fanless – There are fanless power supplies, video cards and heatsinks available.  Having a fanless computer that can stay cool will use less electricity than a computer with fans, but one will be taking the risk of possible overheating.  Therefore, an exhaust fan is recommended at a bare minimum.  An article explaining why can be found at  A CPU heatsink where the fan is optional can be seen at

Computer case – When it comes to the computer case, there is much to consider.  Aluminum computer cases are much better at transferring heat while acrylic cases are one of the worst.  Furthermore, full tower cases handle heat better than mini tower cases.  Therefore, an energy efficient computer case will be an aluminum full tower case.  Tips on how to purchase a computer case can be seen at

Minimize – connect as little as possible to the computer.  Leaving stuff plugged in such as drives and/or PCI cards will consume power while idling.  Therefore, keep the stuff that are absolutely necessary connected, and the rest disconnected.

Using external devices is an option that allows you to plug in the device when required and unplug it when not in use.

Keep it cool – As the parts heat up inside, the energy efficiency decreases.  Therefore, good airflow is important.  Fans may increase in speed to try to keep the temperature inside the case cool.  This results in increased electricity consumption.

I prefer to leave my computer without a panel outside my window in the winter to keep the parts cool, but it will probably get stolen.

An article that shows you how to create a 3 speed fan.  Although, I prefer to buy a part from the local computer store instead.

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