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Recently, I've been seeing many people suggesting the following thing to people looking for help regarding the position of their fan in their case: "No matter what, put your top fans as exhaust because heat rises!"... Wrong! Something you must absolutely have for convection to be applicable is a totally passive environment. As soon as a fan is present, the environment is not passive and the effects of convection are pretty much irrelevant. Here are a few examples of where convection or top exhausts are relevant.
1) Passive PSUs
Some new PSUs are more and more present on the market, these are passive PSUs. These have no fans and therefore rely on passive air movement for cooling (also know as convection). Therefore, you should have the most vented part of it pointing UP (even if you have a bottom vent). This way, the heat that is coming from the PSU components will heat up the air and it will rise out of the PSU. Also, this will help cooling it because your GPU's fan should suck air from the PSU, helping in the cooling. It must noted that this will have almost no impact on the temperature of your GPU since passive PSUs are always very efficient and therefore produce a lot less heat than GPUs.
2) Strict air cooling
By strict air cooling, I mean no radiators. If all your components are cooled by air, you should normally have your top fan(s) as exhaust(s). But, this is not because of convection! This is simply because the component that is the nearest from the top fan(s) is the CPU, a major heat source. Therefore, you wan't the heat to be taken away from the heatsink as fast as possible. Also, this is a good way to keep directional airflow. The top fan will create a low pressure area near the CPU heatsink area which will cause the low pressure area to be filled by the closest source of air. That source should also normally be an intake fan providing cool air for the heatsink's fan(s). If you have a radiator on the back fan, they should always be set up as an intake for the best amount of air. Usually, they will be single radiators hooked up to a CPU cooler like the H Series from Corsair. Therefore, they are cooling the major heat producing component in that area. Because of that, the slightly heated air from the radiator will not cause the temperatures of any components to rise because there's nothing to cool. Of course, there's the VRM area that produces heat but it's a negligable source of heat and could probably be cooled passively in most cases (ie: anything but extreme overclocks on high TDP CPUs).
Now we have seen where your top fan(s) should be set up as exhausts. Sometimes though, you wan't them to be intakes and this is when most misleading advices come.
1) Watercooling
If you have a radiator (Like the H100 or most larger radiators that can only be installed on the tops of a chassis) on the top of your chassis or anywhere else for that matter, it should always be mounted as an intake. This is for various reasons. First, the radiator will only slightly increase the temperature of the air coming in which will not affect the temperature of other components by a significant margin. Also, the radiator is what's cooling the major components in terms of heat production (like a CPU or GPUs) and therefore, that slightly heated air intake will not affect important components except the VRM area which doesn't need much cooling in most cases anyway (ie: anything but extreme overclocks on high TDP CPUs).
Thanks for reading. If you have found any mistakes or believe I have forgotten something, I'd be glad to hear it from you.
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1) Passive PSUs
Some new PSUs are more and more present on the market, these are passive PSUs. These have no fans and therefore rely on passive air movement for cooling (also know as convection). Therefore, you should have the most vented part of it pointing UP (even if you have a bottom vent). This way, the heat that is coming from the PSU components will heat up the air and it will rise out of the PSU. Also, this will help cooling it because your GPU's fan should suck air from the PSU, helping in the cooling. It must noted that this will have almost no impact on the temperature of your GPU since passive PSUs are always very efficient and therefore produce a lot less heat than GPUs.
2) Strict air cooling
By strict air cooling, I mean no radiators. If all your components are cooled by air, you should normally have your top fan(s) as exhaust(s). But, this is not because of convection! This is simply because the component that is the nearest from the top fan(s) is the CPU, a major heat source. Therefore, you wan't the heat to be taken away from the heatsink as fast as possible. Also, this is a good way to keep directional airflow. The top fan will create a low pressure area near the CPU heatsink area which will cause the low pressure area to be filled by the closest source of air. That source should also normally be an intake fan providing cool air for the heatsink's fan(s). If you have a radiator on the back fan, they should always be set up as an intake for the best amount of air. Usually, they will be single radiators hooked up to a CPU cooler like the H Series from Corsair. Therefore, they are cooling the major heat producing component in that area. Because of that, the slightly heated air from the radiator will not cause the temperatures of any components to rise because there's nothing to cool. Of course, there's the VRM area that produces heat but it's a negligable source of heat and could probably be cooled passively in most cases (ie: anything but extreme overclocks on high TDP CPUs).
Now we have seen where your top fan(s) should be set up as exhausts. Sometimes though, you wan't them to be intakes and this is when most misleading advices come.
1) Watercooling
If you have a radiator (Like the H100 or most larger radiators that can only be installed on the tops of a chassis) on the top of your chassis or anywhere else for that matter, it should always be mounted as an intake. This is for various reasons. First, the radiator will only slightly increase the temperature of the air coming in which will not affect the temperature of other components by a significant margin. Also, the radiator is what's cooling the major components in terms of heat production (like a CPU or GPUs) and therefore, that slightly heated air intake will not affect important components except the VRM area which doesn't need much cooling in most cases anyway (ie: anything but extreme overclocks on high TDP CPUs).
Thanks for reading. If you have found any mistakes or believe I have forgotten something, I'd be glad to hear it from you.
