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.
| Construction Material Heat Transfer Coefficients (U) in W/(m2⋅°C) | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Roof Material | Floors | Windows | Walls | ||||||
| Aerated Concrete | 0.16 | Concrete | 1.35 | Metal Frame (single glaze) | 5.7 | Solid Brick | 2.1 | ||
| Clay Tiles | 1 | Pine | 0.13 | Metal Frame (double glaze) | 3.4 | Brick + Insulation | 0.28 | ||
| Felt / Bitumen | 0.3 | Steel | 5.0 | Wood Frame (single glaze) | 4.8 | Solid Stone | 2.25 | ||
| Concrete Tile | 1.5 | Hardwood | 0.18 | Wood Frame (double glaze) | 2.8 | Stone + Insulation | 0.32 | ||
| Shingles (asphalt) | 0.5 | Wood Frame (triple glaze) | 2.1 | Concrete | 3 | ||||
| Wood Shingles | 0.1 | Vinyl Frame (single glaze) | 4.8 | Concrete + Insulation | 0.31 | ||||
| Vinyl Frame (double glaze) | 2.7 | Hollow Wall (air gap) | 1.3 | ||||||
| Vinyl Frame (triple glaze) | 1.9 | Hardwoods | 0.18 | ||||||
| Doors | Pine | 0.14 | |||||||
| Solid Wood | 3.0 | Drywall | 0.16 | ||||||
HVAC (Heating and Cooling) Calculators
- Heat Loss Through a Wall
- Heat Loss from a Room
- Heat Transfer Efficiency
- Heat Transfer Coefficients
- Insulation Calculator