### Category: About Heat

People often say heat rises, but that’s not entirely true. While hot air weighs less than cold air and will naturally rise, heat travels in all directions; from hot to cold. Heat flows between substances when there’s a difference in temperature. If you leave a 32°F ice cube sitting in a 69°F room, heat from the room will transfer into the ice causing it to melt. If both the ice cube and the room are both 32°F, no heat transfer will take place. Theoretically can extract heat from a substance until absolute zero, -459.67°F (−273.15°C) where all molecular motion would stop.

## British Thermal Unit (Btu)

A British Thermal Unit (Btu) is a measurement of heat energy. One Btu is the amount of heat required to raise 1lb of water by 1°F. Btu per hour, or Btuh, is the capacity of a heating system such as a 40,000 Btuh furnace.

With air conditioning, you’ll often hear people express the cooling capacity in tons. The term, “tons,” or “tonnage,” is a Canada/USA refrigeration measurement. The ton of refrigeration is equivalent to using one ton of ice per day when using ice for refrigeration was the standard in the days before switching to mechanical refrigeration.

## Types of Heat

#### Sensible Heat

Sensible heat is the amount of heat, (molecular motion), you can measure with a thermometer. It’s the amount of heat you add or remove to a substance that changes a substance temperature but does not change the state of a substance.

#### Latent Heat

Latent heat is heat added or removed that will change the state of a substance but does not affect the temperature of the substance. Water to steam is a change of state.

## Types of Heat Transfer

There are three types of heat transfer; conduction, convection, and radiation.

#### Conduction

Conduction is the transfer of heat between objects that are in direct contact.

Example: A pot on a stove burner. As the pot absorbs heat, heat will transfer through the pot handle to your hand.

#### Convection

Convection is when a fluid, such as a liquid or air moves from one location to another and carries its thermal energy along with it.