Which of the following is not a unit of heat?

Options

A. BTU
B. Joule
C. Watt
D. Calorie

Answer

To determine which of the following is not a unit of heat, we will analyze each option provided.

### Step-by-Step Solution:

1. **Identify the first option: BTU (British Thermal Unit)**
- The British Thermal Unit (BTU) is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.
- **Conclusion:** BTU is a unit of heat.

2. **Identify the second option: Joules**
- The joule is the SI unit of energy, and it is also used to measure heat.
- **Conclusion:** Joules is a unit of heat.

3. **Identify the third option: Watts**
- The watt is defined as one joule per second and is a unit of power, not heat.
- **Conclusion:** Watts is not a unit of heat.

4. **Identify the fourth option: Calories**
- A calorie is defined as the amount of heat required to raise the temperature of one gram of water by one degree Celsius.
- **Conclusion:** Calories is a unit of heat.

### Final Answer:
Based on the analysis, the option that is not a unit of heat is **Watts**.