If you're running the PC hardware and Air Conditioning, then yes it is a little wasteful, but if you're running the heat in your home it is not really wasteful at all. If you're running any type of heat, then the PC extra cost is about the same in terms of cost per BTU. So you run your PC and use less from your heater.
Any difference between the PC and Mac in energy usage is less than the cost of a daily Starbucks before work. You know you should brew your own Folgers and quit wasting all the money.
The privilege of wasting money is a freedom that most desire.