Biomass Thermal Utilization Act of 2013 or the BTU Act of 2013 - Amends the Internal Revenue Code, with respect to the tax credit for residential energy efficient property, to make qualified biomass fuel property expenditures eligible for such credit. Defines "qualified biomass fuel property expenditure" as an expenditure for property which uses the burning of biomass fuel (a plant-derived fuel available on a renewable or recurring basis) to heat a dwelling used as a residence, or to heat water for use in such dwelling, and which has a thermal efficiency rating of at least 75%.

Allows an energy tax credit until 2017 for investment in open-loop biomass heating property, including boilers or furnaces which operate at thermal output efficiencies of not less than 65% and provide thermal energy.