Our main family room/kitchen is the largest room downstairs, and the only one we heat during the day in the winter. So rather than figure out the complexity and additional cost of an air-to-water, it seemed logical to dip our toes in with something simple.
It's been great. Our gas usage is less than half what it was the previous year. The room heats up faster in the mornings, so there's no need to have the heat on before we come downstairs. On cold days this winter, we were heating the whole downstairs for about 15kwh/day, meaning we're getting roughly a 3-4x COP real-world (closer to 4 i think, but have no way of precisely measuring). If I'm feeling chilly, I can sit directly under it in a nice warm breeze.
It cost £2,275 installed. The model was the Daikin-FTXP60M.
(Recognise that this does not necessarily undermine the argument in the video. But I do find it odd air-to-air source heat pumps are not considered more often in the UK)
Also interesting to compare this relatively modest investment with an electric car. Very roughly, the carbon savings we're seeing are comparable to the savings from replacing 10k miles per annum in an ICE with an electric (I think, rough back-of-the envelope calculation!).