Andrea Rossi, an Italian inventor has developed and is now commercializing a cold fusion reactor that produces heat at a very high power density, roughly comparable to today's nuclear fission plants.
The reaction uses nickel and hydrogen, which fuse to produce copper. This energy rich but extremely clean process is used to heat water. The resulting steam can be used directly as a carrier of heat or be converted to electricity.
There is much development work to be done still but the technology has shown its potential and is being offered in containered 1 megawatt plants.
10 kW home units are planned but not yet available.