In a fireplace, the heat loss q(in Btu/ft^3) resulting from hot gases escaping through the chimney can be?

modeled by q= -0.00002T^2 +0.0203T -1.24, where T is temperature.(the indoor temp. is 65F. For what gas temperature is heat loss maximized? What is the maximum heat loss? Please give detail on how to set it up.Thanks