Info: What's the lowdown on Case Fans? - Overclock.net

ldk · 03-27-05

How many fans should I have in my case? Where should they go? Intake or out? Why? Positive pressure or not? This FAQ will answer these questions and some others. Read on for a cooler case!

Introduction

The purpose of case fans is simple: bring cool air in from the outside and exhaust hot air from the case. The result is a cooler case, cooler components, better performance, and a potentially higher over clock.

You should begin planning your cooling system before setting up your new rig and you should include fans and accessories in your case budget. Realizing that many people have limited funds, we’ll discuss options based on different scenarios. The bottom line is that if you intend to over clock your system you should not skimp on fans and accessories.

Fans and Options

Ok, let’s discuss fans and accessories. Fans come in several sizes, are made of different materials, and have different options. Common sizes for case fans are 80mm, 92mm, and 120mm. Also, different cases may make different provisions for different sized fans. Check your case before you buy so you know how many fans can be installed and where. Some cases also provide snap in fan holders eliminating the need for screws. Most experts recommend a balanced flow of air through your case so I recommend you pick one fan size. This also makes it more convenient if you need to move or swap fans around. I would recommend 80mm as they are adequate for case cooling and can fit in tighter spots like drive bays.

Most case fans are made of plastic. Some models are available in aluminum, but I’m not sure they make a difference in cooling. They might sound differently, but this is a user choice. Plastic is adequate and cheaper.

Case fans are also available in a myriad of different coolers and lighting options. These are fine; however, it is difficult to find a lighted case fan that spins faster than 3000 RPM. The rule of thumb is the higher the RPM the higher the cubit feet per minute (CFM) of air that the fan will move. So if you want your fans to go faster than 3000 RPM and sound like little airplanes you’ll probably have to go with non-lighted fans. For most purposes (including cooling an OC’d rig) 2500-3000 RPM is adequate – provided you have enough fans and they are placed correctly in your system.

The last option we’ll discuss is speed control, which is a neat thing to have. Most fans are capable of this and it allows you to adjust your fan speed to increase cooling capability (speeding the fans up) or reduce noise (slowing the fans down). Check the fans before you buy to make sure they have this option. The rule of thumb is to get fans with 3-pin connectors so you can plug them into a device capable of controlling the speed. Most motherboards offer this option, as do other devices, which will be discussed next. And yes, most lighted fans can be speed-controlled!

Fan Accessories

We’ll discuss three different accessories for fans: filters, grills, and controllers.

Filters

Filters are simple. They are used on intakes only and their primary function is to catch dust. If you use filters make sure you check and clean them on a regular basis (monthly perhaps). Most of the store bought filters can limit air intake, which is not a good thing. Many users come up with field expedient methods like panty hose stretched over the fan. This is probably one of the better and cheaper methods. Make sure that whatever you decide to use is cleaned on a regular basis. If you don’t use any type of filter, make sure to check your fans and case (also clean them!) on a regular basis. Dust will clog your fans and other components, which will eventually cause problems and/or components to fail.

Grills

Grills are neat and can add another dimension of coolness to your case. Make sure you get grills to fit your fans and that you know how to mount them. Grills can also be used where you have no fan if you just want your case to look cooler. Grills come in different materials, designs, shapes, and yes even lighted. There are two different lines of thought on mounting grills. One is to drill holes in the case for the screws. The other is using super glue to secure bolts to the case for the grill mounting screws. I prefer the latter since they look a little neater.

If you decide to drill the holes you should do two things. The first is to use the smallest bit possible for the screw. You can judge this by holding the bit and screw side by side and eyeballing the diameter. You want the drill bit to be slightly smaller than the screw so it bites into the case metal when you screw it in. Don’t over tighten or you’ll strip the hole. If you do, then go find a bigger screw. The second thing is to use a small nail to make a dent in the case so the drill bit doesn’t do a little dance and scratch up your case. You can also avoid this by putting down a piece of masking tape, make the dent and then drill the hole. Use the grill (or fan) as a guide for marking your holes.

If you decide to go the super glue route it’s a little harder, but it gives you a little different look. Select your screws with bolts to fit. Put all the screws in your grill and finger-tighten the bolts to them. Now put a little dab of super glue on each bolt using a toothpick or similar instrument. Place the grill on the case where you want it and press tightly for about 30 seconds. You should be able to slide the grill around a tiny bit if you need to. Once the grill is in place and secure you can remove the screws if you need to. I’ve tried this several times and have yet to super glue the screw to the bolt. The trick is using only a little glue.

Fan Controllers

Most fan controllers are actually dual purpose. They control the speed of your fans and have temperature sensors with displays. Most controllers let you connect up to 4 fans with 4 sensors. I use a Hardcano 12, which can control 4 fans and display temps from 4 sensors. Most fan controllers mount in a 5 ¼ bay and some even have space to mount a hard drive behind the front panel. You can put the temp sensors anywhere you like. I have one mounted on top of the power supply sticking out so I can display case temps. If you do this, make sure the sensor isn’t actually touching the power supply or you’ll be measuring its temp, which is most likely warmer than the air in your case. I put it at the top of my case since that’s where the warmest air is likely to be. I have the other 3 mounted on hard drives.

A Brief Discussion on Hot Air and Holes

There are probably an infinite number of views on fan placement and how many to use. First let’s discuss air and temperature. This is simple – hot air rises. This is a physical law and is almost always the case. The converse of this is that you’ll find cooler air lower than warmer air. So we can deduce from this that we want fan intakes low and fan exhausts high. Right? Right!

Now on to the next point. An air stream will seek to go wherever it can just like water. That means we can channel and control air flow sort of like water in a hose. So what we want is 2 things: (1) make sure that cool air flows in and warm out flows out and (2) make sure there aren’t any holes where air can escape and disrupt our flow. The point of this is that the only entry and egress points in your case should be fan intakes or exhausts. There are many that will argue this point, but that’s fine. This is my opinion and it’s based on researching lab reviews and experience. So, all those nifty holes that come with your case can either be left to disrupt your planned airflow or covered up.

Most of these “holes” are usually found on the back of the case. In deciding whether or not to cover them up you need to think ahead. If you plan on using a water cooling system for your system chips and will be placing your radiator on the outside of the case (which I highly recommend) then you’ll probably mount it on the back somewhere near the top. You really don’t want warm air from your case blowing through your radiator. You want cooler air from the outside. Another reason to block up those holes. Nuff said.

I used that gray Styrofoam stuff that comes as packaging material to block mine. Does the trick and looks neat as well.

Fan Placement

Now back to fan placement. We want the cooler air coming in (from the bottom front) and flowing out through the top rear. Here’s how we can do that.

As a side note, you may want to put your case on the floor since that’s where the cooler air is likely to be. This up to you and may or may not make a big difference. I’ve got mine up on a table where I can see and play with it.

Place two fans set for intake at the bottom front of the case. By the way, you “set” a fan for intake or exhaust by turning it one way or the other. If you look at the fan you can generally tell the front from the back. If you’re not sure, plug it in so you know which is which.

Place one fan set for exhaust at the upper rear of your case. Now you need to check out your power supply and make sure it vents to the outside. Most older power supplies will suck air from the outside and vent the warm air in your case, which is not good. Most new PSU will do the opposite. If you have an older unit that sucks (no pun intended) and are the brave sort, you can open the unit and reverse the flow. I will not recommend that here (its another FAQ or should be) since you can get a nasty shock from the PSU even if it’s unplugged.

Now we should have two front lower intakes and two upper rear exhausts. The air in our case now flows though smoothly (we hope) and everything is cool.

One other note is where in front to put the intakes. Again, differing opinions. You can mount one in a lower drive bay. This way you’ll be cooling your drives, but also blowing warm air into your case. The difference is probably minimal and up to you. I have one fan at the front of my lower drive bay, which has two 120Gb SATA drives (RAID 0) and my case temps never exceed 24*C.

Three fans (not counting those in the PSU) is my recommendation for those on a budget and the minimum recommended configuration.

More on Fan Placement

Ok, so you’ve done everything discussed so far and you’re still not happy with your case temps. No doubt you have a mid-range or high-end graphics card and a highly over clocked CPU, both spitting out heat by the boat-load (otherwise why would you be reading this. Right? Right.).

So what next? Two more fans will help. First, we need to add a side intake. This will help move warm air away from your graphics card. Next, a top blowhole will help exhaust more warm air. Blowholes also look cool too. If you’re case comes equipped with a side fan and top blowhole, make sure the side fan is set for intake and the blowhole is set for exhaust.

If you need to do a case mod to add them – read on.

The best way to cut a hole in your case is to use a hole saw for metal. These things will buzz through steel and cut aluminum like warm butter. I know that some users like to drill a bazillion little holes and then use a jig saw to cut through the holes, then use a file to clean up the ragged edges, etc. Spend the money (~$25 US) and buy a hole saw. You can put it in your toolbox and use it again for all the other rigs you’re going to build, right? Right.

When you’ve decided where to place the new fan hole, make a dent with a little nail (so the drill bit on the hole saw doesn’t do a dance on your case) before making the cut. By the way, the cut will send a lot of little metal slivers down into your case if your cutting a blowhole. I strongly recommend you either remove the top or panel from the case or remove all the components. Use safety glasses, etc.

Once you’ve made the cut, you can use a little file to clean up but with a hole saw you won’t have to do this. Buy some tubing to go around the hole to make it a professional job. You can get this online and I recommend you go with some that has glue on the inside. Measure the tubing carefully and cut it to fit. I recommend you don’t’ make the cut until you’re positive its going to be a good fit. You can always trim it shorter if needed. Putting the tubing on can be quite a chore. You’ll probably have to make several attempts until you get it right.

For fan and grill mounting I recommend you go the super glue route discussed previously.

Conclusion

Hopefully when you’re finished you’ll have case temps around 20-25*C (maybe lower!). If not, go back and review the FAQ and make adjustments. You’re temps will vary since everyone uses different components and tweaks.

The basic rule is this: 2 front lower intakes, 1 side intake, 1 upper rear exhaust, PSU exhaust, and 1 blowhole exhaust. This configuration is highly recommended based on lab tests and results (Computer Power User Magazine and others). By the way, this configuration is also reported to be optimum. No fewer and no more fans will help much. As a matter of fact, more may be worse. If you’ve gone with this configuration and are still not satisfied with your case temps, then get faster fans that move more air (higher RPM and CFM flow).

One other thing you can do is to use rounded cables and make sure you’re not blocking the airflow. Ribbon cables are notorious for this. Use ties to move cables out of the way. It will neaten up your case and allow an unrestricted flow of air.

Remember that your case temps will affect the temp of your components and vice versa.

The higher the over clock, the higher the temps. The lower the temps, the higher the over clock.

Sound confusing? Maybe, but that’s another FAQ.