Audio Research Ref 3 : heat and top space needed?

The REF 3 generates a lot of heat of its top.
Space to the upper shelf depends on the temperature level you have regularly in the room, shelf material and kind of equipment ( tubes or SS ) you have on the upper shelf . 2" space to the upper shelf may not be good enough.

Putting a fan on the shelf is not a good idea since it will vibrate and will be noisy. I use a fan that is hooked on the (upper) shelf. This fan is originally made as aquarium cooler and has special clips for hooking a shelf. I have changed the 12V transformer to a multi voltage transformer, switched to 4.5V so the fan is very quiet.

http://www.shopjebo.com/5/multi_fan_cooling_system_detail.aspx

good luck !