I'll do my best to provide a clear question. I'm not a network/server guy...just a young controls/systems engineer who knows enough to be dangerous :)

My company is working on a major controls upgrade for a jail. I was put in charge of upgrading their video surveillance system. Currently they have an all-analog system sitting in a four post 45u rack. This thing is a mess from the contractor that installed it 6 years ago. No cable management (they had 120 VAC right next to CAT5....smh), and worse yet....no fans in the rack! The sides are closed, the front and back are open (no doors). The top of the rack is a pagoda style with little vents around the top. The client has had DVRs shut down in the rack before from overheating, so currently they have a little fan down on the floor behind the rack blowing on the back of their DVRs. We are re-using the rack, but replacing almost all of the equipment in the rack. We will end up using 28u of the rack space, when all is said and done.

Here's my problem. I want to add fans in the rack for cooling. However, there is another rack about 4 feet behind this one, that stores equipment for their intercom system. I don't want to exhaust hot air out the back of our rack and heat up the rack behind it.

In addition, the HVAC in the room is designed so that cool air comes in, and air is exhausted, from two vents about 6 feet in front of the rack up by the ceiling, 8 feet up.

I can't do anything, within the scope of the project, about rack placement or the HVAC.

My question is, can I exhaust the hot air in the rack out the front of the rack? Or would it be better to put a fan at the top of the rack blowing forward, and set up a few other fans farther down the rack to blow the air backwards? Heat rises, so I figure that I could basically blow the hot air towards the rear further down in the rack; the hot air would rise to the top, and get blown out the top of the rack by a forward-exhausting fan. Lastly, if I went this route, would it be a good idea to put the back door back on the rack to guide the air up to the top? I don't want to put the front door on the rack since there are only a couple of small vents on each door, and there is no way that I'd get enough airflow to exhaust out of the rack.

  • Are the front and back doors solid, or vented?
    – longneck
    May 6, 2016 at 16:27
  • The front and back doors were taken off the rack by maintenance due to over heating. They are in storage. They have some small vents at the top and the bottom, front and back-they don't really provide good ventilation at all. Going off a white paper by Middle Atlantic Products, they recommend 64% minimum open area for airflow, front and back, and these vents don't even come close to providing that.
    – someguy
    May 7, 2016 at 14:55

1 Answer 1


Get mesh doors or leave them off, and make sure to vent front to back. In your case, front should be whichever side faces the air conditioning supply. This may mean installing a device backwards if it vents back to front.

If the HVAC system can keep the ambient temperature everywhere in the room at an acceptable temperature, then this will likely be good enough.

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