Client put in a geothermal heat pump in a vacation rental with personal use (52 rental days, 38 personal use days).  Can he claim all or a portion of the 25D Residential Energy Efficient Property 26% credit?

Q&A #6 in Notice 2013-70 states that it cannot be claimed for an investment property that is not also used as a residence by the taxpayer.   This implies that my client can claim the credit.  Does he claim a portion of the credit?  The entire credit?  Get to depreciate the difference between the cost and the credit?