# What is Temperature?

## What is Temperature?

Bryan covers the critical question: "What is temperature?" He tackles the concepts of temperature and heat, and he explains what they all mean and why they matter to the work we do. There is also a brief section about temperature scales and the similarities and differences between them.

Temperature and heat are related, but they’re not the same. We generally measure heat in BTUs or therms, but temperature is a measurement of the average molecular velocity (kinetic energy) within a substance. Molecules within a single substance move at different speeds, so the temperature is just an average of them all.

In the HVAC industry, we commonly use the BTU or British thermal unit to measure heat. A BTU is the amount of heat it takes to change the temperature of 1 pound of water by 1 degree Fahrenheit.

An 80-degree glass of water and an 80-degree swimming pool have the same temperature. Heat could not transfer between the two, as the average molecule speed is the same. However, there is a LOT more heat in the swimming pool due to the sheer amount of molecules present; the swimming pool has a lot more BTUs of heat contained in it.

We don’t measure quantities of “cold.” However, there is a point where there is a total absence of heat: absolute zero (-460 degrees Fahrenheit, -273 degrees Celsius, or 0 kelvin/degrees Rankine). All molecular activity stops at that theoretical point, and although we can get very close to absolute zero, we can’t reach it. Whereas there is a maximum point of “cold,” heat has no maximum limits.

We can compare molecular velocities to predict the direction in which heat will move. If you feel “cold,” then you feel uncomfortable about the amount of heat leaving your body. You’re more likely to feel cold at lower temperatures because your body heat gets transferred to the environment, which has a lower temperature. Density matters as well, as heat transfers more quickly through water than the air. Ultimately, heat moving INTO our bodies makes us feel hot, and heat moving OUT of our bodies makes us feel cold.

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