[jjk166]

Heat pumps are best for small thermal gradients. If you want your room to be a nice 70F while it's 50F outside, a heat pump is a very efficient way of heating your room. If you want a blow torch that's hundreds of degrees above ambient, a heat pump is terribly inefficient. The exact cutoff where gas heating becomes more efficient is variable, but it's typically a temperature differential between 40 and 60F.