Interesting! Do you cover air-to-air as well as air-to-water heat pumps? I'm still mulling whether the lack of boiler upgrade funding support/need to keep a gas boiler is worth having potential air con in the summer...

Keen to do more on this distinction in future, but so far we've focused on air-to-water as it's more realistic/cheaper for those switching from gas. But as you suggest, air-to-air is compelling, especially for new builds.

We have had air to air ventilation for the last 12y which is fantastic. Not used it for heating but looking to do that.