Start with your utility company; they can help a great deal. How do you know how much is “too much”? Comparing previous bills isn’t always a good measure, as the weather is never exactly the same month to month. Instead, if you take your energy bill and divide it by the square footage of livable space in your home (e.g. don’t count areas like unfinished garages or basements) you can calculate how much you are spending to heat or cool each square foot of your home. Your energy provider can tell you what the average cost per square foot is in your region for that same period of time so you can compare apples to apples.