It depends. You cannot get the tax credit for products used solely for the rental property (ex: any new windows or a water heater for the rental unit). But if there is something shared by the two units (such as an HVAC system or a roof), then you can get half of the tax credit, since half of it is for your principal residence. For example, if you replace the roof and it costs $5000, then the 10% tax credit is $500. You could get 50% of the $500 or $250.

The credit would be reduced by a percentage depending on the number of the rental properties. For example, if you own 4 apartments, and live in one, you would only get 25% of the tax credit. If you have a large home, and rent the basement apartment which is 20% of the space, then you would get 80% of the tax credit.


Source: Section 25C(e) (2) Joint ownership of energy items

(A) In general - Any expenditure otherwise qualifying as an expenditure under this section shall not be treated as failing to so qualify merely because such expenditure was made with respect to two or more dwelling units.


(B) Limits applied separately- In the case of any expenditure described in subparagraph (A), the amount of the credit allowable under subsection (a) shall (subject to paragraph (1)) be computed separately with respect to the amount of the expenditure made for each dwelling unit.