Btu (15.6°C)
The Btu (15.6°C) specifically refers to the energy needed to raise the temperature of water from 60°F (15.6°C) to 61°F.
Newton-meters
A newton-meter (Nm) is primarily used to quantify torque which is the rotational force applied to an object. It is the force of one newton applied perpendicularly to a lever arm one meter long.