In determining the maximum dollar amount of any federally assisted mortgage loan (as defined in subsection (b)) or the maximum per unit or other cost or floor area limitation of any federally constructed housing (as defined in subsection (c)), where the law establishing the program under which the loan is made or the housing is constructed specifies such maximum per unit or other cost on floor area limitation and the structure involved is furnished with solar heating or combined solar heating and cooling equipment under the demonstration program established by section 5503, 5504, or 5507 of this title, the maximum amount or cost or floor area limitation so specified which is applicable to such structure shall be deemed to be increased by the amount by which (as determined by the Secretary or the Secretary of Defense, as appropriate) the price or cost or floor area limitation of the structure including such solar heating or combined solar heating and cooling equipment exceeds the price or cost or floor area limitation of the structure with such equipment replaced by conventional heating equipment or conventional heating and cooling equipment (as the case may be).