James

I'm sorry, I don't remember the exact calculation for BTU's off the top of my head, but the general "rule of thumb" that I use for air circulation is 100cfm per 1000 watts of power. This can seem like a little overkill in some situations since we all know the likelyhood of using all of the power in an amplifier at any one time, especially a multi-channel amp for house audio, is slim to none. Anyway, this simple ratio keeps everyone happy, accounts for extra heat producers like Satellite receivers, and has always worked well for us. We will always try and use a thermostat controlled system so that the heat is always regulated and in most cases will remote mount the fan in the attic or crawl to keep the noise down. If a remote fan is not possible, a good simple solution is a Panasonic quiet fan, made for bathrooms, hooked up to a 120v thermostat, which are available at your local Home Depot or Lowes hardware stores for about $79. These fans are good for the smaller cabinet systems and are good for about 2000-2500 watts. Hope that helps.

Brad