It's not one of the items listed as Major Purchase, but it's possible that it could be considered a
substantial addition to or major renovation of a home, in which case you could add the sales tax to the general sales tax rate as long as it was taxed at the same as the general sales tax rate.
The IRS doesn't specify what counts as a substantial addition or major renovation, as you've probably notioced.An entire HVAC system does count as a capital improvement for depreciation, but there's no mention of this relating to sales tax. I don't see any court cases about this, probably because the amount of tax saved by this addition isn't usually very significant. If you decide to deduct this tax, be prepared to defend that it is a substantial addition or major renovation to your home, rather than a "major purchase."
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