The amount of energy flowing from one body to another body spontaneously, which is due to their temperature difference, we call it heat. Objects of unequal temperatures during thermal systems tend toward thermal equilibrium. The hotter object transfers its heat to the colder object until the objects are the same temperature or in other words, they attain thermal equilibrium. Conduction, convection, and radiation are methods of heat loss. Let us now discuss the heat loss formula in detail.

**What is Heat Loss?**

Heat loss is the decrease of heat existing in space, resulting from heat transfer through walls, roof, windows and buildings surfaces. We calculate heat loss by multiplying the values of the area, the difference in temperatures of inside and outside surfaces and the value of heat loss of the material. Convectional heat loss is the heat loss interest in the ventilation of hot processes.

The total heat loss of the object also involves losses occurring by radiation, convection, and conduction. There is no material, which completely prevents heat loss, we can only minimize the heat loss. Watts is the unit of heat loss.

**Heat Loss Formula:**

\(q = (U × A) × \Delta t\)

Where,

q | Total heat loss |

U | The overall coefficient of heat transmission |

A | Area |

\(\Delta t\) | the temperature difference between inside and outside temperatures |

**Methods of Heat Loss**

**1] Heat Conduction**

Heat conduction, also called diffusion, occurs within a body or between two bodies in contact. It is the direct kinetic energy exchange of particles through the boundary between two systems. Heat transfer by the method of conduction to attain thermal equilibrium when an object is at a different temperature from its surroundings or any other body.

The rate of heat transfer is dependent upon the value of resistance that exists between the different temperatures of two surfaces. Thermal resistance (R) is an ability of an object to retard heat transfer by way of conduction through a given thickness of the substance.

Mathematically, Thermal resistance \((R) = \frac{L}{k}\)

L | insulation thickness |

k | thermal conductivity |

**2] ****Heat Convection**

Heat convection depends on the motion of mass from one region of space to another. And heat convection occurs when the bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter within the fluid.

**3] Thermal Radiation**

Radiation is heat transfer by electromagnetic radiation, such as sunshine, with no need for the matter to be present in the space between bodies. Heat loss to occur from radiation for this the hotter surface temperature should be above ambient temperature, which is much higher than observed in typical heat trace applications.

**Solved Examples for Heat Loss Formula**

Q.1: Determine the total heat loss from the building whose area is 60 sq. m, the coefficient of heat transfer is 0.7 and the temperature difference is 25^{∘}C.

Solution: Given,

- U = 0.7
- A = 60
- \(\Delta t = 25C\)

Substitute these values in the given formula,

\(q = (U × A) × \Delta t\)

q = 0.7 x 60 x 25

Therefore, q = 1050 watts

Q.2. Determine the total heat loss from the building whose coefficient of heat value is 4.5 watt, the Area is 10 m^{2} and the value for ΔT is 5^{∘}C.

Solution: Given,

- U = 4.5 watt
- A = 10 m
^{2} - \(\Delta t = 5C\)

Substitute the values in the given formula,

\(q = (U × A) ×\Delta t\)

q = 4.5 x 10 x 5

Therefore, q = 225 watts

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