you can simply cool the rigs with ambient (correctly done) air flow
I used to keep my rigs cool enough with ambient temps up to 105oF... Now, I realize that's a bit extreme as I know some components (like PSUs) aren't supposed to be in ambient over 95oF (hence all expensive gold-cert PSUs)... but it wasn't too hard to keep all the graphics cards under 75oC. Just had to have a floor fan assigned to each computer... and a huge industrial fan blowing air in from the window & venting out the top..
The door was sealed off with some foam type stuff. I'm sure some of that hot air still got to other parts of the house, but it probably didn't increase the AC bill all that much... maybe 10% or so.