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To optimize the performance your computer and keep it running as smoothly, fast and as reliable as possible, you will have to do some type of maintenance that includes software and hardware. Software maintenance will include installing and updating of drivers, software and anti-virus software and making use of utilities to keep the software environment clean and clutter free.

Hardware maintenance will always start with cleaning of components and the inside of your computer case itself. DEMCiflex Filters were designed to help you keep your hardware clean without the need to open the case.


Negative Pressure

If less air enters the case through the intake fans than air leaving through the exhaust fans the surplus air needed will be drawn in through any other gap or crevice in the case, causing dust to enter the case through this route. These gaps in your case includes all I/O ports, optical drives and other openings in the case. This equates to negative pressure and leads to a very dusty environment inside your case.

Positive Pressure

If more air enters the case through the intake fans than air leaving through the exhaust fans the surplus air will be forced out through any other gap or crevice in the case, preventing dust from entering by this route. This equates to positive pressure.
Positive pressure inside your case will help keep it clean and therefore cooler. In the real world this is more difficult to achieve because of computer cases being very "leaky" and most fans having fairly poor delivery capacity. The more air you put into the case the faster it will run out the other side (through exhaust fans and case openings combined).
This situation however is changing fairly rapidly as cases are being built better and the choice and quality of fans are improving constantly.

How to setup Positive Pressure

If you use a positive pressure airflow setup, the airflow inside the case actually help to keep the inside clean. Less time will have to be spent on cleaning it and the machine will run at it's designed optimum leaving you with more quality time that can be spent on the primary function of your computer. 

Air (and dust) enters and exits your computer case in three ways and if these can be controlled then it would be possible to have a dust free and cool running computer at the same time. These are:

dedicated air intake vents or ports

dedicated air exhaust ports

and most difficult of all to control, all the other openings in the structure of the case. This includes but is not limited to: optic drives like CD and DVD drives, USB, Firewire and all other I/O ports, non air-tight panels and any other crack or opening in the case.

The first two types are fairly easy to control as fans can be used to move predetermined amounts of air in any direction desired. Because of the sheer variety of case types and configurations involved in the third type it will be virtually impossible to control. The secret in achieving this is called "positive pressure" and this concept is widely used in the medical and telecommunication fields (and others) where creating dust free environments are essential. The basics are like this:


All fans have a CFM (cubic feet per minute) rating. This rating tells you how many cubic feet of air the fan is able to move in one minute. A fan's CFM ratings are achieved by various means like fan speed (RPM or revolutions per minute), the size, depth, shape and angle of the fan blades as well as the number of fan blades. Normal 80mm fans have between 6 and 8 blades that push less than 20CFM. To create positive or neutral pressure the total CFM sum of the intake fans must be higher or equal to the total CFM sum of air extracted from the case.

To Calculate what you need to setup positive pressure in your computer or electronic unit's case, please follow the information and instructions below.

Determining CFM ratings of fans

CFM ratings of fans are usually indicated on the packaging or the fan itself but in case of this information not being available, contact the manufacturer of the fan through their websites. If you are unsure contact your dealer.

Factors to take into account

Filter rating - CFM inhibited by filter action (% of filtered intake). By its very nature all filters will affect the flow of air. DEMCiflex Filters has been optimize to have the least affect on airflow while still stopping dust into your unit..

Internal fans - CFM in needed to cool components. These are fans inside the case of your computer and will include CPU fan(s), graphic card fans, HDD cooling fans etc.

Intake fans - CFM in. These fans are situated on the case of the computer drawing air into the case.

Exhaust fans - CFM out. These fans might be found on the case of the computer as well as power supply units and PCI slot fans. It expels air out of the computer case.

Openings in case - CFM in either direction. All other unfanned openings leading into and out of the case

Filter rating: F

This rating will depend on the filter rating you are using. This is expressed as a percentage and is indicated on the packaging. Example: If the filter rating is 15 it will inhibit 15% of the air from entering the computer case. This sum will have to be added to the required CFM of air needed for the intake fan(s) to compensate for the loss of air. Let's call the filter rating value F. Remember that this is a percentage value. DEMCiflex Filters are rated at 20.

Determining the CFM sum of the internal fans: C

Add all the internal fans CFM ratings together. This is the minimum CFM of air that is needed to cool the internal components like CPUs, RAM and graphic cards. Call this value C

Determining the CFM sum of the intake fans: A

Add all the CFM ratings of the fans blowing air from outside the computer case into the case together. Call this value A

Determine the total air intake into the computer: T

Deduct the filter rating value (F) from the CFM sum of the intake fan(s). Call this value T

Determining exhaust fans CFM rating: E

Add the CFM ratings of all the fans blowing air out of the computer together. This will include the power supply unit fan(s), PCI slot exhaust fans and in some cases the graphics card fans. (Some graphics cards have their own exhaust systems.) Call this value E

Determining the CFM sum for openings in the case:
As this value could be positive or negative we can assume that this value will always be equal to the total value of the CFM of air leaving the case. Without intake fans this would be true as the same amount of air will replace the air leaving the case.

Calculating the intake CFM needed:

Internal fans like your CPU and graphic card cooling fans CFM rating can be used to help determine the minimum CFM intake. Intake fans CFM rating must be at least but preferably higher than these combined as this is the minimum amount of air that the computer uses for cooling. When your total CFM sum entering the case (after filter rating is subtracted) is more than the CFM sum leaving the case through the fans it equate to positive pressure. The surplus air will force its way out of the case through any other openings like optical disk drives, card readers etc. and so help to keep these components clean.


  1. Determine the value of C
  2.  If you use DEMCiflex Filters the value of F will be 20%
  3. Multiply F with A. This value is T
  4. T has to have a bigger value than C and bigger than E to achieve positive pressure with adequate cooling. If the T value is smaller than C the components will not get fed enough air to satisfy its demand for cooling. If T is smaller than E negative pressure will be present forcing air(and dust) to be fed through all the unfanned openings to satisfy this demand.