Heat Loss R-Value Calculator:
Enter the values of Surface Area, SA(ft2), Temperature Difference, dT(°F) and R-value, R(sq. ft °F/BTU) to determine the value of Heat Loss Rate, HLR(BTU/hr).
Heat Loss R-Value Formula:
Heat loss through a structure is an important consideration in thermal insulation, determining how much heat is lost through materials used in walls, ceilings, and floors. The rate of heat loss depends on the insulation’s effectiveness, measured by the R-value, which indicates the material’s resistance to heat flow. The higher the R-value, the better the material insulates against heat loss.
Heat loss rate (HLR) measures the amount of heat (in BTU or Watts) lost over a specific surface area (in square feet or square meters) per degree of temperature difference (in Fahrenheit or Celsius) between inside and outside. This calculation is essential for estimating heating needs and ensuring energy efficiency, as it quantifies how much heat escapes through a structure’s surface.
R-value is given by the material thickness divided by its thermal conductivity; hence, lower R-values indicate less insulation and faster heat loss. Calculating HLR helps assess insulation performance and determine how much heating or cooling a space requires to maintain a comfortable temperature. Knowing HLR enables the design of energy-efficient buildings, reducing heating costs, energy consumption, and environmental impact.
The formula for Heat Loss Rate accounts for the surface area of the structure, the temperature difference between the inside and outside, and the R-value of the insulation material. The HLR formula can be used to calculate either the heat loss rate (HLR) when the temperature difference and R-value are known or to determine the required R-value to achieve a specific heat loss rate.
Heat Loss Rate, HLR(BTU/hr) in British Thermal Unit per hour is equal to the product of the Surface Area, SA(ft2) in square feet, the Temperature Difference, dT(°F) in degree Fahrenheit, divided by the R-value, R(sq. ft °F/BTU) in square feet degree Fahrenheit per British Thermal Unit.
Heat Loss Rate, HLR(BTU/hr) = SA(ft2) * dT(°F) / R(sq. ft °F/BTU)
HLR(BTU/hr) = heat loss rate in British Thermal Unit per hour, BTU/hr.
SA(ft2) = surface area in square feet, ft2.
dT(°F) = temperature difference in degree Fahrenheit, °F.
R(sq. ft °F/BTU) = R-Value in square feet degree Fahrenheit per British Thermal Unit, sq. ft °F/BTU.
Heat Loss R-Value Calculation:
1.Calculate the heat loss rate (HLR) for a wall with a surface area of 500 square feet, a temperature difference of 30°F between inside and outside, and an insulation R-value of 15 sq. ft °F/BTU.
Given: SA(ft2) = 500ft2, dT(°F) = 30°F, R(sq. ft °F/BTU) = 15 sq. ft °F/BTU.
Heat Loss Rate, HLR(BTU/hr) = SA(ft2) * dT(°F) / R(sq. ft °F/BTU)
HLR(BTU/hr) = 500 * 30 / 15
HLR(BTU/hr) =1000BTU/hr.
2.A roof has a surface area of 800 square feet with a temperature difference of 20°C. If the heat loss rate (HLR) is 3200 BTU/hr, find the R-value of the insulation.
Given: SA(ft2) = 800ft2, dT(°F) = 20°F, HLR(BTU/hr) =3200BTU/hr.
Heat Loss Rate, HLR(BTU/hr) = SA(ft2) * dT(°F) / R(sq. ft °F/BTU)
R(sq. ft °F/BTU) = SA(ft2) * dT(°F) / HLR(BTU/hr)
R(sq. ft °F/BTU) = 800 * 20 / 3200
R(sq. ft °F/BTU) = 5 sq. ft °F/BTU.