(a) with respect to a taxpayer for the taxable year shall not exceed an amount equal to 4 percent of the average annual gross receipts of the taxpayer for the 3 taxable years preceding the taxable year in which the credit is determined. (3) Gross receipts For purposes of this subsection, the rules of paragraphs (2) and (3) of section 448(c) shall apply. (f) Adjustment of energy efficiency criteria No later than December 31, 2022, and every two years thereafter, the Secretary, in consultation with the Secretary of Energy, shall review the efficiency levels in section (b) and revise these levels upward if necessary to include only the most efficient commercially available heat pumps of each type, while ensuring that at least three manufacturers are represented in each type across a range of product heating capacities. (g) Test procedures (1) The Department of Energy shall develop test procedures to determine Coefficient of Performance for— (A) gas commercial heat pump water heaters, (B) gas commercial heat pumps, and (C) industrial heat pumps. (2) Such test procedures shall build upon the foundation of relevant current American National Standard Institute and International Organization of Standard test procedures. (h) Definitions For purposes of this section: (1) Qualified energy efficient heat pump The term qualified energy efficient heat pump means— (A) any consumer heat pump water heater described in subsection (b)(1), (B) any commercial heat pump water heater described in subsection (b)(2), (C) any consumer unitary heat pump described in subsection (b)(3), (D) any commercial heat pump described in subsection (b)(4), and (E) any industrial heat pump described in subsection (b)(5). (2) Consumer heat pump water heater The term consumer heat pump water heater means a water heater that uses a heat pump to heat water and has an electric input of 12 Kilowatt or less or a gas input of 75,000 British Thermal Units per hour or less, measured in accordance with applicable Department of Energy test procedures. (3)