Mine works down to a remarkably low temperature, but at that temperature is able to extract much less heat than the house needs to stay warm at that outside tem

Mine works down to a remarkably low temperature, but at that temperature is able to extract much less heat than the house needs to stay warm at that outside temperature. So I still burn a noticeable amount of propane, in bursts. A fuel cell driving a heat pump is an interesting notion. The "waste heat" from the fuel cell is not wasted, here. If half the contained energy drives the heat pump at, say, 3x, you get 1.5x vs just burning it. The extra expense of the fuel cell and heat pump seem hard to justify unless you have other uses for them. This is to say that hydrogen for home heating is unlikely to be important.