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I have a recessed shelf which holds three components that each generate heat:

  • A projector
  • A computer
  • An audio power amp

The shelf is located at the top of the wall and open at the front but closed on the 5 other sides. Because of this, the airflow created by the component fans is simply not enough to cool the space and things are beginning to overheat.

I'd like to install a fan to cool the space but not sure what the best placement and airflow direction would be to cool the space. One consideration is the direction of the existing projector fans which create a bit of an airflow pattern on their own. I'd also like to keep the heat inside the house since it's beneficial in the winter.

My question is basically, what is the optimal direction and placement of a single fan in order to exchange the air and cool the space?

EDIT: To clarify, I intend to cut a hole in one of the existing surfaces and install the fan to move air between rooms, and not just to blow air around inside the shelf.

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  • $\begingroup$ Putting your components in the corner of an alcove like this is basically setting yourself up for failure. Those are natural "dead zones." This is a scenario where adding a fan is just not going to cut it, unless you can modify the space to provide another place for air to enter/exit the compartment. $\endgroup$
    – Air
    Jul 20, 2017 at 16:16
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    $\begingroup$ @Air - Sorry if I didn't make myself clear but that is exactly what I intend to do and what I am asking about. One (or two?) of the surfaces / walls will be modified, opened up and a fan installed. THe question is which one and which way to blow. $\endgroup$
    – Eaten by a Grue
    Jul 20, 2017 at 16:21

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You have a couple good options. Don't worry about the fans that cool the pc or projector. They will be of little influence since they are far from the cool air that needs exchanged. Even if they were near a boundary, any tiny benefit in complex considerations like this lost when you upgrade hardware. The key is to look for the source of reliably cool air, existing hvac airflows, and to work with natural convection.

  1. Cool in, existing hole. Place a fan at the bottom of the box near the already open face and blow inward. The projector throw will probalby keep you from going all the way to the front. Closer to the front will be more effective. This requires no new holes, and its flow is not limited by closed doors or other hvac airflows in your house. Simple and reliable.
  2. Hot out, existing hole. Place the fan at the top of the box near the already open face and blow hot air out. Same benefits and limitations as number 1. The difference between these only comes into play when you are worried about enclosure positive pressure and filtering.
  3. Hallway hole, hot out top or cold in bottom. Make sure to cut the hole larger and select a larger grating than just the fan. This will reduce performance with some recirculation, but will ensure your hvac system doesn't fight it and closed doors don't seal it off. The down side is that loud audio will leave your theater room through this hole.
  4. Stairway hole, cold in from bottom. I do not recommend air out the bottom, because you are working against natural convection. This could also have the same noise leaking issues.

On a side note, make sure you purchase a "80+" rated powersupply for your pc. They are 80% efficient or greater and will reduce the amount of heat you have to get rid of. In my experience they are also quite a bit more reliable.

When selecting fans get one with a high cfm (cubic feet per minute) rating and a low dB (decibel) noise rating. Something like this 200mm 700rpm one. If you use more than one fan put them in parallel with both of them on "blow cold in bottom" or "blow hot air out the top". This will effectively double your airflow. Putting them in series with one on hot and one on cold will not increase total air exchange by very much.

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You should also consider placing the 3 components so that they don't "fight" each other for air or one blows onto the other - they all need free access to air. One blowing hot air into the intake of another won't help the second one's cooling.

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Considering this as simillar to a PC case, a large fan (200mm or greater) in the lower side would be fine if you can manage to create a cutout. The flow direction can be outwards (i.e: exhaust) and it should work fine to create a good enough airflow.

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  • $\begingroup$ thanks @ericnutsch, appreciate your in depth analysis. I found a triple fan unit, 21dba, 156 cfm and I'm opting to exhaust hot air into the hallway to the left. this move hot air out of the room and pulls cooler air from below. I also bought a couple small usb fans as an additional option to bring air up through the chase where I ran electrical and audio cable which leads directly into the basement. I only need to drill a couple more holes in the floor plate at the bottom of the chase for this to work - since the air down there is typically about 10° cooler I think this will really help. $\endgroup$
    – Eaten by a Grue
    Jul 24, 2017 at 14:24

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