D.C. Mun. Regs. tit. 9, § 465
465.1 Installation charges for any materials or parts which constitute a repair of existing tangible personal property shall be subject to tax.
465.2 Where an installation charge is made in connection with the sale of a new and complete item the installation charge shall not be taxable if separately stated.
Some examples of exempt installation charges would be in connection with the sale of the following:
SOURCE: Administrative Ruling No. 7, 16 DCRR.