There’s a site with some numbers. Their references are good. Some of the conclusions they themselves draw are incorrect although their end numbers are generally right. (for example, they base their calculation for smart lighting on the number of hours in a year when most people run the lights in anyone’s room no more than three hours a day. But they still get to the right place on their top line because they are using government numbers for the percentage spent on lighting in a typical consumer budget.)
https://www.simplyss.com/blog/smart-home-savings/
Anyway, there are entire government agencies in the US dedicated to nothing but calculating where energy can be saved. So there are a lot of numbers out there without having to go to “private industry.““
According to the energy star folks, about half of the energy used in a typical US home is used to heat space. About another quarter is used to heat water. About 11% is used for lighting prior to getting LEDs. And everything else is everything else.
That’s why smart thermostats generally do pay for themselves pretty quickly. Using cold water to wash clothes will save about 50% of the energy from the washer. Using a more efficient water heater will save energy for sure, but might not save money, because there’s typically a high installation cost.
All of your electrical devices together are running on your electricity, not your gas bill. So there’s usually a pretty high percentage per device that you can save there, but not a lot of dollars. Unless you are running things like pumps and air-conditioners.
I’m not saying you shouldn’t do some kind of energy audit (we use solar energy at our house, so we’re pretty careful about everything), I’m just saying that the total bottom line savings will be impressive in terms of percentage per device, but maybe not so much in terms of cash.
So definitely, more efficient appliances including the furnace, then a smart thermostat, then LED lights, and you’ve probably saved 85% of anything you’re ever going to save.
Smart Meters
Your comments about smart utility meters were spot on. They generally are a closed system that you will not have access to except through a cloud to cloud interface if they make one available. Many utility companies do make those available these days to encourage consumer savings. So the first thing you can do is get in touch with your own utility company and see what kind of energy audits they offer and suggest.