heat pump costs a little more than a gas furnace (around $8,000 vs. $5,000, after rebates), but it is vastly more energy-efficient. In fact, while a gas furnace is always less than 100% efficient (newer models are usually 92–95%), a heat pump can achieve efficiencies of 300–400% (i.e. 1 unit of energy in = 3–4 units of heating out).