How To – Checking And Improving Computer Case Air Flow

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    Today’s Computers need good air flow to keep components cool and adding an additional case fan can often improve the flow of air around your parts but sometimes it can cause harm too.

    In our case we recently replaced the Power Supply which is one of the fans that forces air to exit the computer. In addition since it was only a few dollars we picked up a case fan to replace one that had been making noise.

    Noise from a fan whether it is a case fan, power supply or CPU Fan that is not running fast because of extra load is often an indication that you will soon need to replace the fan.

    When a Fan dies it might lock up while you are using your computer or it may happen when you try to turn your computer on.

    In some instances such as the CPU Fan the computer will sense that the fan is not running and will alert you with a solid beep alarm. You will know the sound when you hear it… it is not pretty. After a few seconds the computer will shut down to protect the CPU from overheating and damage.

    At that point you will need to replace the fan to allow your computer to start.

    If your Power Supply fan dies you will most likely lose power to your computer and it will instantly turn off although this may not always happen. If the power supply fan dies on restarting your computer you will not hear that initial single beep that means power is being sent to your motherboard and your computer is starting the boot process.

    Power supplies are not serviceable and will require replacement. We cover how to replace a power supply in another HowTo and the job is relatively easy although getting at connectors can be difficult since the enclosure is usually rather tight.

    If your Case Fan dies you may or may not get an alert from your computer and it should not restrict the operation of the computer other then the temperature inside the case will be higher and will result in additional load on your cpu fan.

    Checking Your Air Flow

    Checking the Flow of Air exiting your computer is not a difficult thing to do.

    Cut a piece of paper towel about one inch wide and six inches long.

    With your computer on place the piece of paper in front of the fan on the back of your computer and see how much air is exiting by visually remembering the distance and angle of the paper as the fan blows it away from the case.

    Now open the side of your computer as you would if you were servicing the internal parts. This will allow air to flow freely through the case fan or through the Power Supply.

    Is the flow different?

    In our computer the new Power Supply fan and Case Fan were fighting each other.

    Not enough air was entering from the front of the computer and the CPU vent on the side of the case to allow free flow of air out of the Power Supply. If this happens it will shorten the life of the Power Supply and both of the fans.

    Note a very slight difference between the flow when the case is open vs Closed is normal because the fans are creating a negative air pressure in the case. However in our case the fans were struggling so much that flow improved at least 50% when the side of the case was opened.

    Directional Flow of Air In Your Computer Case

    Because computers are stuffed under desks and into small openings that do not often get cleaned manufacturers have found that the best flow pattern for your computer is to have air come in from the front of the case and exit through the back.

    The only exception is the CPU vent in the side of your case that provided air into your case directly to the CPU and that air exits out the back of the case.

    Normally front case fans are not necessary and if you have a secondary fan it will be located on the back of the case below the power supply and in direct line with your CPU to help pull some of the heat out of the case.

    Improving the Air Flow

    To improve the air flow you might first think that turning the case fan around so it blows air into the computer while the Power Supply Fan sucks it out of the case is the best solution unfortunately if you do this you will also be forcing air out of the CPU Vent and reducing cooling in that location.

    You may also think that if you disconnected the fan that would also be good because it will still allow air to flow in from the vents and out through the Power Supply… However this will force 100% of the heat inside the case through the Power Supply and it will shorten its life.

    Since placing holes in the front of the case to improve airflow is not reasonable you could decide to remove one of the drive covers on the front of the case which would allow more air into the case in the proper flow path.

    In our case we have recently installed a new video card that needs extra cooling so we decided to remove two of the unused card slot covers and because they are located on the back of the case we also installed some filter material.

    It is important to filter air that enters from the back of the case because it will likely contain a large amount of dust.

    The Filter

    To make the filter we simply used some extra heating vent filters and some aluminum duct tape.

    Cutting the filter to size you can then apply tape to the edges allowing about a 1/4 inch on and off the filter to allow for easy attachment to the case.

    Installing the filter is easy and the filter can also be cleaned with compressed air from a can when you are performing other work on your computer.

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