I haven’t seen the Georgia Tech study, but these numbers don’t add up. The average yearly household electric bill is indeed at least $1,200 (NPR: 908 kWh @ $0.12/kWh), but this is just for electricity. That doesn’t include gas (CNNMoney: household average is $357/mo, or $4417/year) for driving, or natural gas or other fuel for heating. The $37,550 of efficient hardware would save electricity, but also gas (the car) and heating fuel (Nest thermostat; hot water heater and dryer if run on natural gas). Without doing the math, I would expect the payback period to be under 10 years, or well within the expected lifetime of most of these appliances.