There are two types of credits, the first page covers solar, wind, geothermal and so on (energy production, basically) and the second page covers non-business energy efficient building property (furnace, windows, insulation, etc.)
Your heat pump water heater will go on line 22a as "energy-efficient building property." It also must meet the appropriate efficiency standard (UEF of 2.2 or higher).
Note the credit is 10% of the cost of the water heater plus installation, with a maximum of $300. There is also a lifetime maximum of $500 for this credit so if you previously claimed any credits for a furnace, air conditioner, doors, windows or insulation, your credit now may be reduced or disallowed.
Line 22a. Enter the amounts you paid for energy-efficient building property. Energy-efficient building property is any of the following.
• An electric heat pump water heater that yields a Uniform Energy Factor of at least 2.2 in the standard Department of Energy test procedure.
• An electric heat pump that achieves the highest efficiency tier established by the Consortium for Energy Efficiency (CEE) as in effect on January 1, 2009.
• A central air conditioner that achieves the highest efficiency tier that has been established by the CEE as in effect on January 1, 2009.
• A natural gas, propane, or oil water heater that has a Uniform Energy Factor of at least 0.82 or a thermal efficiency of at least 90%.
