I did some calculations on the interwebs based on 50W draw at idle (which is way more than it really is as the amp is 15W) and it comes to about $32 per year if I leave it on for 12 hrs a day. My electric bill can increase that much every month based on the weather so I am not really worried about $30/yr.The only thing that's going to be hurt by leaving a tube amp on all day is your electric bill.