Heat loss through wall

The Heat Loss through a Wall calculator computes the amount of heat energy that conducts through a wall based on the temperature variance, surface area and coefficient of heat transmission.

INSTRUCTION: Choose units and enter the following:

• (A) Surface Area of Wall
• (Ti) Interior Temperature
• (To) Exterior Temperature
• (U) Coefficient of Heat Transfer in (W/m²⋅°C)

Heat Loss Through Wall (HL): The heat loss is returned in  watts and BTUs per hour.  However, these can be automatically converted to compatible units via the pull-down menu.

The Math / Science

The formula for heat loss through a sur face (e.g., a wall) is:

 HL =  A ⋅ U ⋅ Δt  

    where

•     HL = Heat loss (W)
•     A = Exposed Surface Area of exposed surface
•     U = Coefficient of overall heat transmission in W/(m²⋅°C) (see table below)
•     Δt = Temperature Delta on either side of the surface

Coefficient of Heat Transmission (U)

The U-value, also known as the heat transfer coefficient, measures the rate at which heat transfers through a material or assembly of materials (like walls, windows, roofs, etc.). It is a critical factor in determining the thermal performance of building elements.

The U-value is expressed in units of watts per square meter per degree Celsius (W/m²°C) or in Imperial units, BTU per hour per square foot per degree Fahrenheit (BTU/h·ft²·°F). Essentially, it indicates how much heat energy passes through a specific material or assembly per unit area and per degree of temperature difference between the interior and exterior environments.

A lower U-value indicates better insulation properties because it means the material or assembly has lower heat conductivity and reduces heat transfer more effectively. Conversely, a higher U-value signifies higher heat transfer and poorer insulation properties.

U-values are used in building design and construction to ensure energy efficiency, as they help determine the insulation needs for various components like walls, windows, roofs, and doors. Lower U-values are desirable in colder climates to minimize heat loss from the interior, while in warmer climates, they can help reduce heat gain from the exterior.

HVAC (Heating and Cooling) Calculators

• Heat Loss Through a Wall
• Heat Loss from a Room
• Heat Transfer Efficiency
• Heat Transfer Coefficients
• Insulation Calculator

Heat Calculators

• Specific Heat from Change in Temperature
• Specific Heat from Two Temperatures
• Specific Heat Lookup Table
• Heat Energy Needed to Change Temperature