My mining rig (2x 7970 and 2x 5970 - approx. 1200W) is installed in the basement of our house. Window is open and airflow is ok. It is quite warm in that room (only 9 square meters in size), but as the basement is not lived-in, heat is not a problem. CHP generation plant is installed right next to it and this is much louder when in operation and also generates more heat.
AC for houses is not very common in europe and so we do not have one installed. In summer we had 35 C (approx. 95 F) and no problem with the rig.
By the way - for fire prevention, i installed one of these directly over the rig:
http://www.fkofireknockout.com/webshop/images/fkokom4t56.jpg