These days we are all aware of global warming and climate change and we are constantly reminded of our responsibility to minimize our environmental impact through, amongst other things, the efficient use of fuel. It is this quest for higher efficiency which has driven the development of the Merlin 600E, a gas-fired hot water system which operates at an extraordinarily high thermal efficiency of 95%. Due to this extremely high efficiency, the Merlin 600E produces 75% less greenhouse gas than an electric storage water heater, 36% less than some gas-fired storage water heaters and between 20% and 30% less than other gas-fired continuous flow and instantaneous water heaters. It even produces less greenhouse gas than a typical electric boosted solar water heater.