I run cards in a dedicated place with ventilation so just default fans..
If you run these at home you will *need* extra fans blowing air on the cards if you want to actually live in the house.
(Well.. Even if you put them in a basement, many cards next to one another will still run very hot)
The fan noise of these cards at 100% is absolutely unbearable.
Actually measured ~85dB with a professional Extech decibel tester a few meters away, which is not that far away from a small jet engine.
Anyway, if you want to cool a ton of rigs at once, try these. They are very power efficient for the amount of CFM provided.http://www.seabreeze.ca/fans/TurboAire/turboaire.html
Home Depot, Costco and some other big retailers routinely carry these in their inventory.