If you purchased the HVAC in 2015, did you apply for the home energy credit on your 2015 return (if your unit qualifies) and if you were under the max lifetime limit? It is reported on Form 5695.
If you didn't claim an energy credit you were qualified for in 2015, it is retroactive according to that Energy Star site.
" These tax credits are available for purchases made in 2016, as well as retroactive to purchases made in 2015."
Section 106 of the PATH Act of 2015 simply makes permanent the option to claim an itemized deduction for State and local general sales taxes in lieu of an itemized deduction for State and local income taxes. This option was already available for 2015 prior to the signing of the PATH Act and 2015 TurboTax's interview provided you the ability to select this option.