The reason most people don't use it is that it costs a fortune to install initially and is dependent on local geology. The payback is longer than most people ow

The reason most people don't use it is that it costs a fortune to install initially and is dependent on local geology. The payback is longer than most people own their houses for and anecdotally the advertised payoffs have been reduced due to efficiencies standard systems. This further reduces the incentives.