Heat Loss Calculator

Find how much heat escapes through a wall, window or roof component.

How the Math Works

The Heat Loss Calculator uses the formula heat loss = U-value × area × ΔT to quantify energy loss through building components. The U-value represents the thermal transmittance of a material, measured in watts per square meter per degree Kelvin (W/m²K), indicating how easily heat passes through it. The 'area' refers to the surface area of the component (e.g., walls, windows) in square meters. ΔT (delta T) is the temperature difference between the inside and outside of the building in degrees Celsius or Kelvin. Multiplying these three factors gives the total heat loss in watts, which shows how much energy escapes through that specific component.

Practical Applications

To apply this calculation, first determine the U-value of the building material from manufacturer data or industry standards. Measure the surface area of the component in question. Then, record the indoor and outdoor temperatures to calculate ΔT. Input these values into the calculator to find the heat loss. This helps architects and builders size heating systems correctly, compare insulation options, or assess energy efficiency. For example, upgrading a window with a lower U-value can significantly reduce heat loss, as demonstrated by recalculating with the new U-value to project energy savings.

Day-to-Day Use

Understanding heat loss helps homeowners and businesses reduce energy waste and lower utility bills. By identifying weak points like poorly insulated walls or single-pane windows, individuals can prioritize cost-effective improvements such as adding insulation or replacing components. This knowledge also supports environmental goals by decreasing energy consumption and carbon emissions. Additionally, knowing heat loss can improve comfort by ensuring heating systems work efficiently, preventing cold spots in rooms and maintaining consistent indoor temperatures year-round.

Worked example

200 ft² wall, U 0.3, ΔT 40°F → 2,400 BTU/h.

FAQ