Forums DIY Ground Source Heat Pumps Reply To: Ground Source Heat Pumps October 25, 2018 at 2:44 pm #446 keith 10 Posts I have ASHP – get some proper advice. You need an up to date energy cert, and then ideally a thermal model of the house (our installer did all this) to size the rads and the ASHP. Ours is paying for itself in no time thanks to RHI and saving vs oil.