[matrss]

> A heat pump that is used on the exhaust of a low efficiency furnace might turn it into a high efficiency furnace.

Just to make this clear: I was already comparing to a high efficiency furnace. I.e. a standard air-to-water heat pump (relatively common as a heat pump at least here in germany) would be more efficient at heating a house with electricity purely generated from natural gas than a natural gas furnace would be at its theoretical limit of 100%.

> This would have other benefits because you would not have to throw away an old furnace for no reason.

As long as there are no synthetic fuels for those furnaces (that can be made climate neutral) there is a very good reason to get rid of all of them: any burned fossil fuel is too much burned fossil fuel. We need to get down to zero.

[cousin_it]

> I.e. a standard air-to-water heat pump (relatively common as a heat pump at least here in germany) would be more efficient at heating a house with electricity purely generated from natural gas than a natural gas furnace would be at its theoretical limit of 100%.

It seems to me that scheme from my toplevel comment (point 2) was already more efficient than either of those. Namely, you burn the gas in the home, and use the temperature gradient to also run a heat pump vs the outside.

[matrss]

> Namely, you burn the gas in the home, and use the temperature gradient to also run a heat pump vs the outside.

I am not exactly sure what that would look like, but I'd imagine it would at least be difficult to match the efficiency of a combined cycle power plant to generate electricity at home for the heat pump. Then again, as you say, you would have the "waste" heat locally to harness as well. Although this waste heat in power plants can be used for district heating as well, so it might also be used in that situation.

Anyway, my main point was that the sentence "heat pumps make much more sense when you don't burn things to power them." makes it sound like burning the same thing to heat your house directly was more efficient when in fact it is not, and potentially by a pretty wide margin.