Fans and Grilles to Cool a TV Cabinet

A cabinetmaker gets help figuring out how to get enough air moving to cool a big, hot television unit. July 11, 2007

I have posted a couple of things about the cooling challenge I am facing in the entertainment center I am building. I solved the fan issue, but now I have a question about the grilles I have to build.

The fan has a diameter of 4-3/4" which gives an area of a little less than 17-3/4 sq. in. I am pairing the fans so the area is 35-7/16 sq. in. total. Do I need to have the same area of opening on the grilles that I build? Should it be bigger?

Forum Responses
(Cabinetmaking Forum)
From contributor R:
The grills should be bigger. You will need to figure the free area of the grill. Depending on the type, the free area could be 50% so the grills would need to be twice as big. The bars or slats on the grill take up space that will require pressure to overcome. So the grill must be bigger.

From the original questioner:
I guess I didn't post the question clearly, or I don't understand what your reply says. When I asked about the sq. in. area, I meant the free area should match the sq. in. area of the fans. Or does the free area need to be larger than the fan area due to the pressure of the slats in the grille? The final size of the grille is determined only by the hole. Is this correct?

From contributor R:
Right, the hole area should be the same. The free area should at least match the fan. The air velocity at the grills would be the same as the air velocity at the fans, which is fast. If you make the grills bigger, the velocity will be less (and maybe less noise). I would double the area to slow down the air and reduce noise.

From contributor E:
If you have two fans pushing air out, where is the air being pushed in from? Your cabinets are probably tight, which means you are trying to create a vacuum in the cabinet. I would cut two holes for incoming air as well. I have found one fan in and one fan out is better than four fans out.

From the original questioner:
The cabinet doors must be open when the equipment is in use. This serves two purposes: 1) The remotes will work (I didn't want to use an infrared button on the outside, thereby forcing the doors to be open), and 2) It allows air to be drawn through the cabinet, and consequently across the equipment, with the fans being in the rear.

On the plasma cabinet, it will be an open front, so the two fans in the rear will have no problem drawing their supply. Like I stated earlier, I know this client fairly well, and the less he has to think about this stuff, the better it will be for his equipment.