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Sorry to have been unclear - my comment was a response to this specific claim, which only considers power generation via natural gas, not the grid as a whole, n

Sorry to have been unclear - my comment was a response to this specific claim, which only considers power generation via natural gas, not the grid as a whole, nor coal: "Due to transmission losses, it is cheaper, efficient, and greener to combust natural gas for warmth directly than to burn it at a power plant, feed the power into the grid, and use grid power to run a heat pump." This statement does leave itself some wiggle room with "cheaper", but in terms of "efficient" it cannot really be true, because the average efficiency of a natural gas power plant is 45% - and if I'm reading this document correctly, that figure already factors in transmission loss: https://www.eia.gov/todayinenergy/detail.php?id=44436 https://www.eia.gov/todayinenergy/detail.php?id=44436

nkurz 4y ago
Good points, but in case anyone is still reading, I feel compelled to stick to my guns: I think it matters where you are. Figures 7 and 8 in this 2022 paper from Lawrence Berkeley Lab give maps of the seasonal minimum heat pump COPs necessary to achieve cost and CO2e equivalence with a 95% efficiency gas furnace: https://escholarship.org/content/qt8pt9155c/qt8pt9155c.pdf https://escholarship.org/content/qt8pt9155c/qt8pt9155c.pdf. It requires making some assumptions about heating season air temperatures, but I think it shows that with current electricity generation there are several states where air source heat pumps are actually worse for emissions. And that at current energy prices, there are several states (not necessarily the same) where they are not a win for running costs. Betting on the future "greening of the grid" is a good argument, but the timescale matters. I like the future of heatpumps, but I worry about a backlash if the benefits are oversold.
- marssaxman 4y ago
  I appreciate your attention to accuracy in this discussion. I think we are basically arguing against different oversimplifications, not really disagreeing about anything fundamental. My own house was built with hydronic floor heating, via natural gas. We added a ductless heat pump a few years ago, but we primarily use it for cooling. It would be a clear win from an environmental perspective, since our utility is 80% hydro and 0% coal/oil/gas; but the radiant floors are so much more comfortable that we haven't made much use of electric heating yet. We'll probably have the heat pump upgraded in a year or two, to cover more of the house; perhaps that'll be a good moment to shift our habits and see how it works out.
  - nkurz 4y ago
    They aren't real common, but there do exist air-to-water heat pumps that can be used for radiant floors. They usually aren't hot enough for pre-existing baseboard, but hydronic flooring runs cooler. Not sure about availability, but here are some specs from a Canadian manufacturer: https://www.arcticheatpumps.com/specifications.html https://www.arcticheatpumps.com/specifications.html.

nkurz 4y ago

Good points, but in case anyone is still reading, I feel compelled to stick to my guns: I think it matters where you are. Figures 7 and 8 in this 2022 paper from Lawrence Berkeley Lab give maps of the seasonal minimum heat pump COPs necessary to achieve cost and CO2e equivalence with a 95% efficiency gas furnace: https://escholarship.org/content/qt8pt9155c/qt8pt9155c.pdf https://escholarship.org/content/qt8pt9155c/qt8pt9155c.pdf. It requires making some assumptions about heating season air temperatures, but I think it shows that with current electricity generation there are several states where air source heat pumps are actually worse for emissions. And that at current energy prices, there are several states (not necessarily the same) where they are not a win for running costs. Betting on the future "greening of the grid" is a good argument, but the timescale matters. I like the future of heatpumps, but I worry about a backlash if the benefits are oversold.

marssaxman 4y ago
I appreciate your attention to accuracy in this discussion. I think we are basically arguing against different oversimplifications, not really disagreeing about anything fundamental. My own house was built with hydronic floor heating, via natural gas. We added a ductless heat pump a few years ago, but we primarily use it for cooling. It would be a clear win from an environmental perspective, since our utility is 80% hydro and 0% coal/oil/gas; but the radiant floors are so much more comfortable that we haven't made much use of electric heating yet. We'll probably have the heat pump upgraded in a year or two, to cover more of the house; perhaps that'll be a good moment to shift our habits and see how it works out.
- nkurz 4y ago
  They aren't real common, but there do exist air-to-water heat pumps that can be used for radiant floors. They usually aren't hot enough for pre-existing baseboard, but hydronic flooring runs cooler. Not sure about availability, but here are some specs from a Canadian manufacturer: https://www.arcticheatpumps.com/specifications.html https://www.arcticheatpumps.com/specifications.html.