(An index of the fuel cost to heat 1,000 liters of water that assigns electricity a baseline score of 100, scores petroleum at 97, diesel at 77, and a heat pump-by far the cheapest-at just 23.)
以燃燒 1,000 公升水量的成本來說，若電力成本為 100 %，石油則為 97 %、柴油為 77 %，熱泵只要 23 %。