My only overhead is electricity for cooling and powering the machines, the cooling will be easier in the next few months yes. I'm the only person I know that's praying for the temperature outside to drop! Hahah If it drops lower and difficulty goes higher, obviously the lifespan of my machines shortens dramatically and thus I get less profit than I originally forecasted, but due to my business model, I normally break even on my hardware within a few days, so I don't have that to worry about