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Removing computer generated heat from behind desk

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Sep 21, 2013, 04:28 PM
Removing computer generated heat from behind desk
I have a desk built into the wall in my home. It's appx 8' long, 3' deep & 3.5' tall. The table top is deeper than the desk itself, so I can get behind it (for wiring computer, phone, etc.)

The desk has a built in cabinet for the computer tower (which I use.) There is appx 8" of space between the computer tower and wall(the table top goes flush to the wall.)

Anyway, heat from the computer comes out where my legs are - under the desk. And it's HOT. I've been thinking of ways to remove the heat - and came up with a few things:

* Cut a larger hole in the top of the desk and install a fairly large computer case fan (140mm.) Connect it to power, and then install a manual switch that can be activated as needed (maybe installed under the desk?)

* Obtain a thin piece of wood/plastic that would ensure heat would be routed appropriately and block off the area between my legs and behind the desk.

Now, there are a few issues with this (at least as far as I can tell):

1. Making a giant hole in my desk.

2. Wiring a fan designed for a computer into an ac adapter and installing a switch. I don't know how to do this.

Thoughts please?

This message has been edited. Last edited by: yuckypants,
Sep 21, 2013, 05:22 PM
You can use a small bath fan instead of a computer fan. One simple way would be to mount the fan high on the wall up near the ceiling. You can use the wall cavity as a duct and cut a hole covered with a grill cover down low behind the desk. This could work of a regular switch or you cold get really clever and wire it to a thermostat installed in the cavity behind the desk.

Another option would be to block off the area where the desk cavity opens on to your feet. If there is an opening towards the end of the desk, then the hot air can exit there. Even if the space between your feet and the wall is only a few inches, as long as it is sealed and the hot air has another path to follow, it will keep it off of your legs. If you do have a continuous 8" space, just installing a piece of 1/2" foam board along the back of the desk should work fine to redirect all the hot air to the desk end.

This message has been edited. Last edited by: Jaybee,

Sep 21, 2013, 05:33 PM
I think the first option is a fantastic idea, but far too advanced for me!

However, regarding teh second option - I always wanted to block off that space, but I wanted to make sure that there was some sort of venting in place before I closed it off. Do you think a mid-size computer case fan will be sufficient to facilitate the removal of hot air?

I figured I'd install the fan on the underside of the desk (hole cut on top) to expel the hot air. I'd have to install a grate on the top as well so small stuff can't fall down into it and break it.

Regarding power, I initially was considering converting the molex adapter to ac and then installing a manual switch, but others recommended that i just use the computer's power (only needs to be on when the computer is on anyway.) I could either:

1. Get a usb case fan and use the usb ports on the back to power it.
2. pull the molex connector to the outside of the case and plug the fan in.

Regarding closing off the cavity - a friend suggested wood veneer.

Foam board it is. I was just researching - and this is THE way to go.

This message has been edited. Last edited by: yuckypants,
Sep 21, 2013, 05:34 PM
Your configuration is similar to some I've seen in offices where I've worked. The desktop unit is way too enclosed and doesn't have enough air flow space.

I'm not sure that cutting a hole in the top of the desk to install a fan will help unless the fan can be placed right smack in back of the tower, which is where the heat is generated. Or were you considering upgrading the fan within the tower?

And with the top of the desk flush to the wall, the heat can't rise upward.

Is there any way you can move the tower up on top of the desk and angle it so the fan isn't as closed in and the heat can flow outward?

Also, and I don't know how to check this but are you sure your fan is operating properly? Have you always felt heat near your legs? I've felt the back of my computer when it's acting up and warm, and it's warm, but it's never been "HOT". And are you certain the heat is coming from the tower? I assume you've put your hand back there and can feel it exiting from the back of the tower.

I had a problem when it's 90+ and had to angle my tower away from the wall to provide more space for the fan to vent the heat. It's awkward, but it works.

I'm not a computer expert, so these are just some amateur thoughts, but I'm sure there will be some other more sophisticated comments.

But that is a nice desk; did you build it?

This message has been edited. Last edited by: GardenSprite,
Sep 21, 2013, 06:49 PM
The fans in the tower are awesome, so no need to upgrade those.

I'm not sure why you don't think heat would escape from the top. The desk surface (top) goes all the way to the wall, but the back of the cabinet where the tower is located doesn't. If I seal off the portion between my legs and the cabinet, air can only escape through the front of the cabinet or a hole cut in the top of the desk, it would use the path of least resistance, right?

I cannot move the tower up - I have 4 23" monitors on the desk. There is literally no room. Plus, I don't want to.

And yes, I'm positive that the fans are operating properly - the problem is, the path of least resistance is on my legs. I want to redirect it somewhere else - and since heat naturally rises, I wanted to vent out to the top.

So I'm proposing I cut a hole in the top of the desk - large enough for hot air to dissipate.

Heat will naturally rise and exit via the freshly cut hole in the desk. Should I also install a 140mm fan to help air removal? It's not a sealed system, but I hate the warm air on my legs.

Oh and no, did not build it - came with the house when we bought it. There is also some other custom woodwork that matches (a bookshelf and some shelves above the tv area.)

This message has been edited. Last edited by: yuckypants,
Sep 21, 2013, 08:10 PM
On further thought, you should be able to do this without any fans at all. Currently there are two basic problems to fix - heat getting trapped and the easiest path for the heat to escape being at your feet.

So, seal off the back of the desk - the foam board will work well. Then all you need is a path for the heat to escape - ideally a place for cool air to enter the space behind the desk (lower) and an exit point up high. I'm still wondering if the end(s) are open - if so, then just blocking off the path to your legs should work.

Sep 22, 2013, 01:00 AM
Right now, air enters through the front (in and around the computer), and by my legs. If I seal off the area by my legs, then air can only enter via the front of the cabinet (door stays open when the tower is on anyway.)

If I create a hole on top for air to exit and block off a path to my legs, would that be enough? Or are you suggesting that I leave a small gap on the bottom of the foam board for cool air to enter?

Also, I was thinking about a 3" circular hole. Do you think that's large enough?
Sep 22, 2013, 10:29 AM
You definitely want to seal off and space between your legs and the space where the computer (and heat) is. Hard to say if 3" is enough but I would doubt it. If you go without a fan and are using natural convection, then you need two openings - one down low for cooler air to enter and one up higher for hot air to escape. In essence, your desk cavity space is working like a tiny attic.

If you are going to use a fan to pull the hot air out, then you still need a (smaller) opening down low with the fan mounted up high. For such a small space, a 3" fan should do the trick, but now you are back to your original plan of finding a fan and make all the electrical connections.

I'm still wondering about the ends of the desk. Is this 8" deep by 3' tall space behind the deck open on either end? If so, then that's more than enough open space to let the heat escape and all you need is to keep it from getting to your legs. Simple is always better - if you can vent the space, keep it away from your legs and keep the computer running cool without a fan, I'd go for that route.

Sep 22, 2013, 01:24 PM
I've included some pictures with captions to show in case my explanation is sub par:

Air enters here: It's not forced induction (with the exception of the computer):

Airflow: Air as it passes through the cabinet and computer. Proposed foam sheets blocking air from entering leg area (picture point of view taken from leg area, as it provides access.):

Proposed exhaust port: On the underside of the desk. Again, fuzzy area is foam sheets blocking air from entering leg area:

Proposed vent hole: View from the top of the desk. IF a fan was installed, it will be installed on teh bottom of the hole, and then a grate would be installed on top to prevent items from falling inside:

Hope this helps.
Sep 22, 2013, 01:36 PM
what is on the other side of the wall? Maybe you can vent, with the aid of a fan into that room. this would be good if the room isn't used when the PC is on, like a bedroom? best if it's an outside wall

This message has been edited. Last edited by: nona,
Sep 22, 2013, 01:43 PM
This was my first consideration. It's the garage.

However, a user on another forum said:

Having a hole between your garage and interior can introduce issues with gasses entering your home as well as providing an easy route for fire to take in case a fire started in your garage.

Venting into the wall isn't a great idea either. Depending on where you live this could cause condensation in the wall and mold issues.

I'd recommend installing a vent on the front of the cabinet to bring in cool air and then push the hot air up and out at the back.
Sep 22, 2013, 02:05 PM
The pictures really help. I would do this:

Get a fan like this from Lowe's:

You an mount it directly underneath the desk top or use a short piece of flex duct to isolate any noise and vibration. Then, cut out the kick plate below the computer cabinet (or drill a line of 1-1/2" holes). Also drill 1-1/2" holes around the perimeter of the floor of the computer cabinet. this will allow air to be drawn in while keeping the front door closed to the computer cabinet.

Add the foam barrier to isolate the computer area from your feet.

Wire the fan to a simple switch. If it turns out that the fan is too noisy, then get a 3 speed fan switch and replace the standard switch.

Also I will confirm that you do not want to vent into the garage area. That's a firewall and cannot have any openings.

This message has been edited. Last edited by: Jaybee,

Sep 22, 2013, 02:23 PM
I actually prefer having the front of the cabinet open while the computer is on. Would this be detrimental to my setup if I left it open? i.e., would air not flow to the proposed exhaust vent properly?

Also, I have a 140mm computer case fan. I planned on just using that and connecting to the computer. When computer is on, fan is on. Thoughts?
Sep 22, 2013, 04:07 PM
Both of these ideas will work fine - in fact, leaving the door open will help a lot and eliminate the need to drill all those holes I mentioned.

With such a small area, just about any fan will work. All you need is a little positive airflow that draws hot air someplace other than at your feet.

Sep 24, 2013, 12:10 PM

Thank you very much for all of your input and advice. Since this is my first home, I want to make sure that everything I do - is the right way. Even if I have to hire a professional or wait longer due to funds, etc.

Though this is just a desk, I also know it's easier to repair holes in walls than it is holes in desks!

Thanks again!
Oct 10, 2013, 12:31 PM
I have a desk with a tower case inside it. I love having the computer hidden and quiet but it overheated.

I used a hole saw to drill a 3" hole near the bottom front of the side of the desk (input air to the PC tower case) and another 3" hole on the upper rear of the side of the desk (where the PC power supply is).

I then bought a 120v fan from eBay (search 120v fan under computer & parts) and a couple of extra fan guards.

Like this:

I put the fan on the rear opening, mounted inside the desk, blowing out. I used rubber washers on the fan to try to isolate all the vibration I could.

For the front, I just covered the front hole with a guard to keep dust bunnies down and prettify it some.

It worked very well and, since it's a computer fan, it's very quiet.
Oct 10, 2013, 06:02 PM
This is perfect! My exact situation!

However, I have a question, and then a proposal and would appreciate your feedback:

1. How does the fan power on? Do you have a switch installed, or do you just need to plug it in?
2. I've considered these, but I actually have 2 spare 140mm case fans that I would rather use. For many reasons, but the main being that I want it to power on when I start the computer and power down when it's turned off. I have a port on the back of the tower that will allow me to pull wiring out of the case for a device (it's got a rubber piece that is strikingly similar to a garbage disposal splash guard ( This way, I could utilize the computer's power to operate the fan (without having to wire an additional switch.) Of course, I would wrap the fan's cable in insulated (corrugated) tubing to prevent nicks or cuts.

What are your thoughts on this?