Good call. Though, if you use natural gas for heating and water heating and don't own any AC... It'll be a lot less energy in total and you'll notice a new gaming PC. Especially if it coincides with a new game you've been playing nonstop for a few weeks. But I agree, there are a lot of electrical devices in a regular home. And my usage changes with the seasons. For example I watch a lot more TV when it's rainy and cold outside, and the TV is like 100W. And I turn on the lights hours before I'd need them in summer. And it's difficult to tell apart the things in a home just by looking at an electricity bill.

You should have a look at your computer, though. Have you had a look at powertop? And I suppose there is a tool for AMD graphics cards to tell you if it's running at full speed all the time or clocking down as it's supposed to. Or you could get a power meter to plug your PC in to. And do a measurement with GPU and one with the thing ripped out entirely.