[Marsymars]

Is gas actually less efficient? I haven't had to work out the math myself yet, but there are some very salient variables - e.g. what's the energy source of the electricity? If it's a natural gas power plant, you're looking at like 30-60% efficiency of gas->electricity in the first place. Are you looking a at a heat pump heater? If so, how much of its energy would be pulling heat from the house that needs to be replaced by the home's heating supply anyway?

This is the kind of thing where a carbon tax is great for sorting out the pricing to match the externalities.

[Spivak]

You might be right, I'm just talking about "last mile" efficiency. I get electricity at $/kWh and gas at $/therm and then an electric heater is x% at converting that electricity into hotter water and a gas heater is %y. From what I can find y < x for water heaters on the market. But even despite that my $/therm is so low that it still comes out ahead.

[Reason077]

> ”Are you looking a at a heat pump heater? If so, how much of its energy would be pulling heat from the house that needs to be replaced by the home's heating supply anyway?”

Heat pump water heaters pull heat from the outside. Usually with a split outdoor unit, just like normal A/C and heat pump systems.

I’ve also seen models where the entire system (integrated storage cylinder for the heated water) is installed outdoors, but those are presumably meant for more mild climates.

In any case, they certainly don’t pull heat from inside the house.

[Marsymars]

Thanks, that obviously makes more sense. (I think I was thinking about heat pump clothes dryers at the same time I was making that comment.)

[Reason077]

Heat pump dryers don’t cool the room either because they work in a closed loop. There’s no external vent removing hot air to the outside like a conventional dryer. So they pull heat from the room but also put it back in the room, and the overall effect is to warm up the room slightly.