The installers will have info, there is I believe a grant now, because we are expecting some money back next year for our recently installed air to air heater.
The one we had installed a few years ago did not attract a grant because of the fact that it can be reversed to become an air conditioner in summer time, and there were (unbelievably in France where many people have died from heat in various canicules) no grants for aircon. This has now changed.