For existing homes, owners should pay a plumber to install a "drain water heat recovery unit", assuming the price of copper is reasonable. It's one of those low

For existing homes, owners should pay a plumber to install a "drain water heat recovery unit", assuming the price of copper is reasonable. It's one of those low hanging fruits that will improve the energy efficiency of every home with minimal effort. Likewise, insulation can be added to hot water pipes to increase efficiency even further.