240v is two 120v power sources but at different phases. It is more efficient. You should only operate at about 5760 Watts continously on that circuit but you aren't far over it. If you have to run a lot of wire, consider a larger size wire so you can size up your breaker and change out your receptacle to make more power available.

What size in amps is your current panel, 200amp or less? You might want to install a subpanel in the garage if your non-mining power consumption in your house is pretty low.