Am I saving money or not? Will x device save me money on my energy bill? This is probably one of the most asked questions when it comes to performing upgrades on your house. There are so many "energy savings" devices out there, its hard to know what works, what doesn't, and the load of smoke they blow up your nose when trying to sell a product.
You see so many internet ads claiming this device will save x amount of money over time once you install it. Obviously I am not naming any products names, because there are too many of them out there, and some of these people are so blatantly obnoxious(I have seen them on youtube threaten to "knock their teeth out") that I don't feel like going to court or getting sued.
But, one thing the majority of them do is show you savings based off last years energy bill. Really, that's how they do it. Why is this a bad idea? Why does this not work? Well, for one thing there is no guarantee that for the month of march, in 2009 you used the exact same power as you did in march of 2010. Or 2008, or whatever year they fill like using. Power schemes change from year to year, as does energy usage, as does temperature and weather conditions. Maybe last year was really hot, or really cold and this year was really mild. Why don't they show you from 10 years ago? Or 5? I have seen many years a 18 to 20% difference in energy bills(power used not cost) from corresponding months, based on nothing but a fluke in weather extremes.
Long story short, using energy bills to compare or show savings is a faulty means of correlation. Look for verified lab testing on devices, because that is the ONLY means of proof there can be to identify savings. And make sure the testing was done by a recognized lab, not the manufacture in their garage(I have seen that as well). If this data isn't available, be sure and google the product for blogs or reports that have been published on the device. Or, ask your local utility. They are always willing to help, and many have a list of approved or verified devices that are proved to save energy.