A company called "Intelligen" out of Hopkinton, MA brought out a line of cogenerative domestic heating units in the 1990s. Based on a Lister engine of some sort, the device had auto start which was actually controlled by the house temperature. I.e. temperature drops, unit self starts, unit generates in "induction generator" mode putting power back out on the power lines. Meanwhile, unit operation continues and heats the house with waste heat meanwhile accumulating a credit on the electric bill. Thus you had only one energy input to your house, namely No. 2 oil to the engine/generator, and you get "free" electric power.
The units were kind of pricey at nearly $5K. Payback was estimated at perhaps 5 years. And with the induction generator there was no backup power - the grid was required for the unit to work.
Intelligen still exists but has followed the marketplace into the "independent & backup power" route for businesses, shopping malls, government offices.
Joe