Big price difference comes from installation of ground loop. They either dig up your back yard and install a horizontal loop or you can have a vertical borehole

Big price difference comes from installation of ground loop. They either dig up your back yard and install a horizontal loop or you can have a vertical borehole (you probably need several of those). Boreholes here in NE-EU are about 35EUR per meter and for my house I'd need about 300m of them.