[mikewarot]

You're assuming the amount of waste heat is greater than the heat required in the house, which could very well be true.

I was assuming the heat required was far more than the waste heat output of the device.

[Schroedingersat]

All that's required is for the temperature of the waste heat to be higher for it to be a waste (assuming a close to carnot or reduced carnot efficiency).

Of course if your heat pump's efficiency doesn't scale with temperature ratio there might a way to use the heat to move it towards carnot efficiency.

[sidewndr46]

If you aren't getting enough heat from whatever this fuel-cell thing is, you would just run another heat source. You could in fact just run a regular heat pump at that point, which would get you more heat for the house.