I'm posting this here as a one-stop thread for all of your air cooling needs. I consider myself pretty adept at optimal air cooling, so I will just devote this FAQ to air cooling. It would be cool (no pun intended) if we could get a water cooling expert to post a Water Cooling FAQ to keep this thread reasonable in size and scope. This FAQ is a bit of science, a bit of experience and a bit of common sense. However, my knowledge isn't perfect and this may include mistakes like typos and just flat out wrong information. I also may need to clarify some things or include some things, so feel free to chime in.
How does air cooling work?
Have you ever put a hot piece of food in your mouth? If you have, you learned pretty quickly to blow your food before eating it. Air cooling works the same way except in a more continuous manner. In the past when CPUs were only a few MHz, they did not generate enough heat to warrant any type of cooling. However, as CPU speeds reached into the hundreds of MHz, some sort of cooling was needed. The first type of cooling devices were known as Passive Cooling devices. They had no moving parts and relied heavily on natural processes for thermal transfer and heat dissipation. If you put a hot object next to a cooler object, some of the heat from the other object will tranfer to the cooler object. If the heat source is gone, then eventually both objects would be the same temperature, this is called equilibrium. Technically a processor and HS will never reach total equilibrium because the CPU continually generates heat, but the closer to equilibrium they are, the safer. Passive devices dissipate heat at a slow rate. The larger the heat sink, the better the cooling. This is so because the heat has a larger surface area in which to dissipate thus providing better cooling. However, since these devices dissipate heat slowly, active heat sinks came into the picture. These simply added a fan to speed up the air dissipation process thus providing better cooling. Of course, larger and faster fans provide better cooling.
What is CFM?
This stands for Cubit Foot per Minute (or cubic meters per second to the European inclined) and is a measurement of the amount of air over a surface area for a specific amount of time. In layman's terms, this is basically how much air a fan blows on an object. The larger the fan, the larger the CFM. The faster the fan, the larger the CFM. Remember what active cooling does? It dissipates heat faster than passive cooling can. So it follows that if you have a larger and faster fan, then you'll have better heat dissipation. Of course, this comes at a price...noise. You'll notice that when you purchase a fan for your heatsink or system, you'll see both the CFM and the noise level (in dB) listed. There's a trade off. Personally, I enjoy the white noise from my loud computer. It helps me sleep better.
What is thermal grease/paste and how does it work?
Thermal grease/paste is a lubricant/heat transfer agent derived from metals like silver or other ingredients. Thermal grease is used to bridge the gap between the CPU and the heat sink to provide better thermal transfer. No HS has a 100% flawless surface so thermal compounds like Arctic Silver fill in the microscopic gaps in the surface so the heat can seamlessly transfer from one surface to the other. The most popular thermal grease among enthusiasts seems to be the Arctic Silver brand. Personally I use AS Ceramique. It's a bit pasty, but at least I don't have to worry about shorting my components since it's ceramic-based instead of metal-based like AS 1-5.
Why is my CPU temp higher than my friend's when we have the same model?
This is a main point of panic for some novice system builders and overclockers. However, there are many other questions that you need to ask yourself before you want to pop open the case or RMA your CPU.
1. Are the computers in different environments?
Simply put, a Pentium 4 in an attic in August will run much hotter than a Pentium 4 in a 64F office. With CPU cooling the environment is just as important as the heatsink/fan and the case fans.
2. Where are you getting the temperatures?
A temperature diode built into the chip will give you much more accurate temperatures than a third party device with the sensor stuck between two fins of your heat sink. Never compare your native temps to a third party hardware sensor in another system. Of course yours will be higher because it's closer to the source and more accurate.
3. What temperatures are you looking at?
Some people have been known to panick when they look in the PC Health Status and see seemingly astronomical values. Most AMD chips for example have a diode on chip that measures the CPU die temperature...that is the actual temperature of the CPU core. Some motherboards may supplement this with another CPU reading, which measures the socket temperature. Most motherboards measure the socket temperature and the motherboard temperature. Here's an example of this using Speed Fan. Notice that my Die temp is 54C but the CPU temp is 39, it even gives the motherboard temperature. For me, 39C is all I care about. The die temp is supposed to be high. According to AMD specs, my die temps can go up to 80C before I worry about processor damage. Luckily, most motherboards have an anti-burn feature that shuts the system down if the temperature threshhold is reached.
4. Do you have identical hardware?
If you two bought the same model Dell on the same day and your temps are astronomically different, then yeah, there may be a problem. However, if you have four high RPM hard drives, a 6800U and a beefy PSU, don't be surprised if your system is a bit warmer than a system with one hard drive, a 9600 Pro, and a 250W PSU. More hardware in the box means more hardware generating heat in a confined area. If you have one 80mm fan blowing air out the back, then yeah, you'll see higher temps.
Make sure you ask yourself all of these questions before you blow $50 on a new HSF and a ducting mod.
5. Are you overclocking?
If you're running higher than stock speeds, then expect higher temperatures than the stock model. Most overclockers invest in higher end HSF to compensate for the increased heat.
How do I get the best cooling?
A whole lot goes into getting optimal air cooling. I am an advocate of starting from the top down, so I'll give you some factors to consider when air cooling.
1. Start with the room temperature
That's the first thing I'll tell you, because unless you have your PC ducted to an AC unit, your CPU temperature will NEVER be lower than the room temperature. That's a natural fact. Room temperature is the standard by which you should always measure your temps. My ad hoc formula for CPU temperature is CPU >= C >= R where C is the case temp and R is the room temp. Theoretically everything should be equal, but that won't happen because of some factors like hardware and air flow. However, by experience and observation, I've found that the CPU should be around delta 10C the case temperature and the case temperature delta 5C the room temperature (delta is the change between two values, for example 20C is delta 5C of 15C). So if your room temp is 25C, then your case temp should be around 30C and your CPU around 40C. Give yourself +-5 playing space. If you have a room temperature of 25C and your CPU temp is 50-60C then there's a problem with air flow or your cooling solution. However, if your room temp is 40C and your CPU temperature is 60C, then invest in an AC unit before you complain on the message boards.
2. Is their proper air flow? Do you have a lot of hardware?
First and foremost, I'd be a hypocrite if I started preaching proper wire routing. My Case is the epitome of poor wire management with a lot of hardware in the box. Let's learn from my bad example. First and foremost, my wire planning is non-existant. I didn't think too much when I connected stuff. If there was a free molex, then I plugged it in. Secondly, I have rounded cables (which are a plus), but the ones I used for the RAID configuration are much too long. Secondly, I have a lot of hardware in the box. Should I expect high case temperatures? You bet I should. At any rate, you need to make sure that the air that comes into your system can flow freely over the motherboard. You want the air to be like a rushing rapid, not a stagnant pool or whirlpool.
A good way to see if what your temperatures SHOULD be is to take the side panel off of the system and let the temperature go down to its lowest value. That's your goal, that's the magic number. Some may scoff at this method and say, "Of course it's going to be cooler, the side panel is off!" Well, taking the side panel off allowed obstructed air to get into the case. The question you need to ask is, "Why couldn't that air come in before?" Then you need to think of a way to get that air in. See, without your help, the warm air will be trying to leave your system and the cold air will try to come in. Thanks to the natural process of diffusion, everything tries to reach equilibrium. When you spray potpourri in a corner of the room, after a while it spreads throughout the whole room. That's diffusion, the movement of something from an area of high concentration to an area of low concentration. The eventuality is equilibrium where everything is equally dispersed. So even if you don't have a single case fan there will be SOME type of air flow (albiet miniscule) due to diffusion. All we want to do is help that process along by FORCING cooler air in and FORCING hotter air out. This is acheived best by including case fans. The more, the better, the bigger (remember CFM), the better. However, there's a trade-off when it comes to noise level.
There are many opinions when it comes to fan configuration, but I'll keep it simple: Focus more on getting cool air in. Personally I have three intakes and two exhausts. Some people prefer their exhaust at the top, but we all have roommates and family members that like to put boxes and books on top of the case, so I'd include rear fans just in case. However, it's important to include at least one intake fan.
That's all for me. Feel free to add other useful air cooling tips.
How does air cooling work?
Have you ever put a hot piece of food in your mouth? If you have, you learned pretty quickly to blow your food before eating it. Air cooling works the same way except in a more continuous manner. In the past when CPUs were only a few MHz, they did not generate enough heat to warrant any type of cooling. However, as CPU speeds reached into the hundreds of MHz, some sort of cooling was needed. The first type of cooling devices were known as Passive Cooling devices. They had no moving parts and relied heavily on natural processes for thermal transfer and heat dissipation. If you put a hot object next to a cooler object, some of the heat from the other object will tranfer to the cooler object. If the heat source is gone, then eventually both objects would be the same temperature, this is called equilibrium. Technically a processor and HS will never reach total equilibrium because the CPU continually generates heat, but the closer to equilibrium they are, the safer. Passive devices dissipate heat at a slow rate. The larger the heat sink, the better the cooling. This is so because the heat has a larger surface area in which to dissipate thus providing better cooling. However, since these devices dissipate heat slowly, active heat sinks came into the picture. These simply added a fan to speed up the air dissipation process thus providing better cooling. Of course, larger and faster fans provide better cooling.
What is CFM?
This stands for Cubit Foot per Minute (or cubic meters per second to the European inclined) and is a measurement of the amount of air over a surface area for a specific amount of time. In layman's terms, this is basically how much air a fan blows on an object. The larger the fan, the larger the CFM. The faster the fan, the larger the CFM. Remember what active cooling does? It dissipates heat faster than passive cooling can. So it follows that if you have a larger and faster fan, then you'll have better heat dissipation. Of course, this comes at a price...noise. You'll notice that when you purchase a fan for your heatsink or system, you'll see both the CFM and the noise level (in dB) listed. There's a trade off. Personally, I enjoy the white noise from my loud computer. It helps me sleep better.
What is thermal grease/paste and how does it work?
Thermal grease/paste is a lubricant/heat transfer agent derived from metals like silver or other ingredients. Thermal grease is used to bridge the gap between the CPU and the heat sink to provide better thermal transfer. No HS has a 100% flawless surface so thermal compounds like Arctic Silver fill in the microscopic gaps in the surface so the heat can seamlessly transfer from one surface to the other. The most popular thermal grease among enthusiasts seems to be the Arctic Silver brand. Personally I use AS Ceramique. It's a bit pasty, but at least I don't have to worry about shorting my components since it's ceramic-based instead of metal-based like AS 1-5.
Why is my CPU temp higher than my friend's when we have the same model?
This is a main point of panic for some novice system builders and overclockers. However, there are many other questions that you need to ask yourself before you want to pop open the case or RMA your CPU.
1. Are the computers in different environments?
Simply put, a Pentium 4 in an attic in August will run much hotter than a Pentium 4 in a 64F office. With CPU cooling the environment is just as important as the heatsink/fan and the case fans.
2. Where are you getting the temperatures?
A temperature diode built into the chip will give you much more accurate temperatures than a third party device with the sensor stuck between two fins of your heat sink. Never compare your native temps to a third party hardware sensor in another system. Of course yours will be higher because it's closer to the source and more accurate.
3. What temperatures are you looking at?
Some people have been known to panick when they look in the PC Health Status and see seemingly astronomical values. Most AMD chips for example have a diode on chip that measures the CPU die temperature...that is the actual temperature of the CPU core. Some motherboards may supplement this with another CPU reading, which measures the socket temperature. Most motherboards measure the socket temperature and the motherboard temperature. Here's an example of this using Speed Fan. Notice that my Die temp is 54C but the CPU temp is 39, it even gives the motherboard temperature. For me, 39C is all I care about. The die temp is supposed to be high. According to AMD specs, my die temps can go up to 80C before I worry about processor damage. Luckily, most motherboards have an anti-burn feature that shuts the system down if the temperature threshhold is reached.
4. Do you have identical hardware?
If you two bought the same model Dell on the same day and your temps are astronomically different, then yeah, there may be a problem. However, if you have four high RPM hard drives, a 6800U and a beefy PSU, don't be surprised if your system is a bit warmer than a system with one hard drive, a 9600 Pro, and a 250W PSU. More hardware in the box means more hardware generating heat in a confined area. If you have one 80mm fan blowing air out the back, then yeah, you'll see higher temps.
Make sure you ask yourself all of these questions before you blow $50 on a new HSF and a ducting mod.
5. Are you overclocking?
If you're running higher than stock speeds, then expect higher temperatures than the stock model. Most overclockers invest in higher end HSF to compensate for the increased heat.
How do I get the best cooling?
A whole lot goes into getting optimal air cooling. I am an advocate of starting from the top down, so I'll give you some factors to consider when air cooling.
1. Start with the room temperature
That's the first thing I'll tell you, because unless you have your PC ducted to an AC unit, your CPU temperature will NEVER be lower than the room temperature. That's a natural fact. Room temperature is the standard by which you should always measure your temps. My ad hoc formula for CPU temperature is CPU >= C >= R where C is the case temp and R is the room temp. Theoretically everything should be equal, but that won't happen because of some factors like hardware and air flow. However, by experience and observation, I've found that the CPU should be around delta 10C the case temperature and the case temperature delta 5C the room temperature (delta is the change between two values, for example 20C is delta 5C of 15C). So if your room temp is 25C, then your case temp should be around 30C and your CPU around 40C. Give yourself +-5 playing space. If you have a room temperature of 25C and your CPU temp is 50-60C then there's a problem with air flow or your cooling solution. However, if your room temp is 40C and your CPU temperature is 60C, then invest in an AC unit before you complain on the message boards.
2. Is their proper air flow? Do you have a lot of hardware?
First and foremost, I'd be a hypocrite if I started preaching proper wire routing. My Case is the epitome of poor wire management with a lot of hardware in the box. Let's learn from my bad example. First and foremost, my wire planning is non-existant. I didn't think too much when I connected stuff. If there was a free molex, then I plugged it in. Secondly, I have rounded cables (which are a plus), but the ones I used for the RAID configuration are much too long. Secondly, I have a lot of hardware in the box. Should I expect high case temperatures? You bet I should. At any rate, you need to make sure that the air that comes into your system can flow freely over the motherboard. You want the air to be like a rushing rapid, not a stagnant pool or whirlpool.
A good way to see if what your temperatures SHOULD be is to take the side panel off of the system and let the temperature go down to its lowest value. That's your goal, that's the magic number. Some may scoff at this method and say, "Of course it's going to be cooler, the side panel is off!" Well, taking the side panel off allowed obstructed air to get into the case. The question you need to ask is, "Why couldn't that air come in before?" Then you need to think of a way to get that air in. See, without your help, the warm air will be trying to leave your system and the cold air will try to come in. Thanks to the natural process of diffusion, everything tries to reach equilibrium. When you spray potpourri in a corner of the room, after a while it spreads throughout the whole room. That's diffusion, the movement of something from an area of high concentration to an area of low concentration. The eventuality is equilibrium where everything is equally dispersed. So even if you don't have a single case fan there will be SOME type of air flow (albiet miniscule) due to diffusion. All we want to do is help that process along by FORCING cooler air in and FORCING hotter air out. This is acheived best by including case fans. The more, the better, the bigger (remember CFM), the better. However, there's a trade-off when it comes to noise level.
There are many opinions when it comes to fan configuration, but I'll keep it simple: Focus more on getting cool air in. Personally I have three intakes and two exhausts. Some people prefer their exhaust at the top, but we all have roommates and family members that like to put boxes and books on top of the case, so I'd include rear fans just in case. However, it's important to include at least one intake fan.
That's all for me. Feel free to add other useful air cooling tips.
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