Here's an analysis I did a few years back when evaluating whether to install an air-to-air pump: https://observablehq.com/@robinl/retrofitting-air-source-heat-p

Here's an analysis I did a few years back when evaluating whether to install an air-to-air pump: https://observablehq.com/@robinl/retrofitting-air-source-heat-pumps https://observablehq.com/@robinl/retrofitting-air-source-hea... I installed it at a cost of around £1,500, and it's been great. It probably is a relatively expensive method of carbon abatement, however. At the time, I was comparing against an electric car, and I concluded it was a significantly cheaper way of reducing my carbon impact (we only drive around 10k miles a year) For reference, it reduced my gas usage from around 10k KWh to 5k KWh, resulting in a reduction in emissions of around 500kg a year