if you're concerned that one mining rig is going to generate excess heat in the space you supposedly have available,
then i'm concerned about your plans to expand your mining operation.

also, it's a dumb argument, that keeping the cards at stock will save on electricity costs, and thus be better for shareholders.
it's dumb because the radeon 5970s are about the most power efficient cards out there,
thus, the more power you pump into them the better ROI you will get.