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Heat Loss Formula

Decrease of heat existing in space, resulting from heat transfer through walls, roof, windows and buildings surfaces or other factors is known as heat loss.   

Heat loss is determined by multiplying the values of the surface area, difference in temperatures of indoors and outdoors and value of heat loss of the material.

The heat loss interests in ventilation of hot processes which is known as convectional heat loss. The total heat loss of the object involves losses occurring by radiation, convection, and conduction.  

Heat loss is measured by the units called Watts.

Heat loss formula is expressed by,

q = (U × A) ×Δt


q = total heat loss through the building in Btu/hr,

U = Overall coefficient of heat transmission through the building,

A = the area in sq.ft of the building assembly with coefficient of heat transmission U,

Δt = temperature difference between inside and outside temperatures.

Example 1

Determine the total heat loss from the building whose Area is 6.0 sq.ft, coefficient of heat transfer is 0.7 and the temperature difference is 25C.



U = 0.7

A = 6.0

Δt = 25C

Substitute these values in the given formula,

q = (U × A) ×Δt

  = 0.7 x 6.0 x 25

Therefore, q = 105 watts

Example 2

Determine the total heat loss from the building whose coefficient of heat value is 265 watt; the Area is 4.30 meters and the value for ΔT is 1135 watts.



U = 265 watt

A = 4.30 metres

ΔT = 1135 watts.

Substitute the values in the given formula,

q = (U × A) ×Δt

  = 265 x 4.30 x 1135

Therefore, q = 1293332.5 watts