(1) For investments in products installed on or after July 1, 2010, the following applicable specification must be met or exceeded to qualify for the credit:

(a) Exterior windows and skylights-U factor less than or equal to 0.30;

(b) Storm windows-U factor less than or equal to 0.30 when measured in combination with the exterior window over which it is installed;

(c) Exterior doors-U factor less than or equal to 0.30;

(d) Storm doors-U factor less than or equal to 0.30 when measured in combination with the exterior window over which it is installed;

(e) Split system central air conditioning-EER greater than or equal to 13 and SEER greater than or equal to 16;

(f) Package system central air conditioning-EER greater than or equal to 12 and SEER greater than or equal to 14;

(g) Split system air source heat pumps-HSPF greater than or equal to 8.5, EER greater than or equal to 12.5 and SEER greater than or equal to 15;

(h) Package system air source heat pumps-HSPF greater than or equal to 8, EER greater than or equal to 12.5 and SEER greater than or equal to 14;

(i) Natural gas or propane furnace-AFUE greater than or equal to 95;

(j) Oil furnace-AFUE greater than or equal to 90;

(k) Hot water boiler-AFUE greater than or equal to 90;

(l) Advanced main air circulating fan-no more than 2 percent of total energy use;

(m) Heat recovery ventilators-CSA C439-00 standard;

(n) Gas, oil, or propane water heater-energy factor greater than or equal to 0.82 or thermal efficiency of at least 90 percent;

(o) Electric heat pump water heater-energy factor greater than or equal to 2.0.

(2) For doors and windows installed on or after January 1, 2015, only the additional cost expended to exceed the requirements of the IECC as amended and adopted by the Montana Department of Labor and Industry qualifies for the credit. An individual calculates the additional cost by comparing the actual amount expended to the estimated, retail cost of installing an item that is substantially similar in style and design and that also meets the required rating. For example, the credit cannot be based on comparing the retail cost of an ornate, solid-wood door to the cost of a less ornate, fiberglass door.