Replacing a gas boiler with a heat pump in the UK cuts emissions by 77-86%.
This includes the embodied emissions from manufacturing the heat pump.
This means the heat pump would offset its embodied carbon after 13 months.
https://www.carbonbrief.org/factcheck-18-misleading-myths-about-heat-pumps/
@icanbob @janrosenow they usually use the national electricity average emissions over the year. But it depends when you set your heat pump to fill the tank. I set my heat pump to run when the electricity is the cheapest, 1000-1600 (usually finishes at 1200) and this is when the grid is on 70% renewable (WA, Aus network average is 40%). Also I have solar so it's free.
@dean @janrosenow I did this study of solarPV and my GSHP last winter. In Ontario it isn’t possible to do what you describe.
https://energyasicit.ca/solarPVpaper2/