The term 'heat unit' is used to describe a variety of different measurements. The crossword solutions for this term include 'therm' (5 letters), 'CALORIE' (7 letters), 'LAP' (3 letters), 'PIECE' (5 letters), 'COP' (3 letters), 'ERG' (3 letters), and 'BTU' (3 letters). A therm is a unit of energy equal to 100, 000 British thermal units (BTUs). A CALORIE is a unit of energy equal to 4.184 joules. A LAP is a unit of energy equal to 4.186 joules. A PIECE is a unit of energy equal to 4.2 joules. A COP is a unit of energy equal to 4.1868 joules. An ERG is a unit of energy equal to 10-7 joules. Finally, a BTU is a unit of energy equal to 1, 055 joules.