Welcome    if you’re planning a house that is airtight and well insulated, don’t bother with RHI as it will never pay back the “MCS Premium” that it will cost to get it installed. Beware you can’t just “do a course” to become MCS accredited and there is significant cost to the person who wants to become a registered installer. This isn’t just about becoming certified on an ASHP install, there is significantly more to it.    I would focus on getting the heat demand down and then