Building Star Energy Efficiency Act of 2010 - Establishes in the Department of Energy (DOE) the Building Star Energy Efficiency Rebate Program of 2010.

Directs the Secretary of Energy to issue rebates to building owners to offset a portion of the cost of purchasing and installing qualifying equipment or materials or undertaking qualifying services to enhance the energy efficiency of existing commercial buildings and multifamily residential buildings.

Prescribes rebates for the purchase and installation of qualifying: (1) insulation, windows, and qualified high-efficiency window films and screens; (2) new energy efficient equipment, such as boilers, furnaces, and water heaters; (3) unitary air conditioners and unitary heat pumps; (4) variable speed drives for motors; and (5) interior lighting.

Prescribes calculations for reductions in: (1) installed lighting power resulting from installation of qualified interior lighting; and (2) annual energy usage resulting from installation of qualified exterior lighting.

Prescribes calculations also for rebates for qualified: (1) replacement chillers; (2) qualifying services to enhance the energy efficiency of buildings; (3) energy-efficient building operation and maintenance training; (4) service on space heating equipment and cooling systems, (5) energy monitoring and management systems with analog controls; and (6) HVAC testing, balancing, and duct sealing.

Directs the Secretary to: (1) establish a Building Star Energy Efficiency Loan Program to make grants to states to support financial assistance provided by qualified program delivery entities for making energy efficiency and renewable energy improvements to existing buildings that qualify under the Building Star energy retrofit program.

Amends the Energy Policy Act of 2005 to: (1) direct the Secretary to make guarantees for energy efficiency projects, including projects to retrofit residential, commercial, and industrial buildings, facilities, and equipment; and (2) authorize the Secretary, in the case of programs that finance such retrofitting, to offer loan guarantees for portfolios of debt obligations, and to purchase or make commitments to purchase portfolios of debt obligations.