Heat Load Calculator

About the Heat Load Calculator

Calculates the conductive heat loss/gain through a surface from its area, U-value (thermal transmittance) and the indoor-outdoor temperature difference.

How to use this calculator

1. Enter the U-value, which measures how easily heat passes through the material.
2. Enter the surface area, in square units like m or ft.
3. Enter the temperature difference, 94T, between the two sides.
4. Read the heat load, Q, which tells you the rate of heat transfer.

The formula explained

The calculator uses \( Q = U A \\Delta T \), which computes heat load from the U-value, the area, and the temperature difference. A larger U-value, larger area, or larger temperature difference all increase \( Q \).

• Q = heat load, or rate of heat transfer
• U = U-value, the overall heat transfer coefficient
• A = surface area
• \(\\Delta T\) = temperature difference between the two sides

Step by step method

1. Find the temperature difference using \( \\Delta T = T_{\\text{inside}} - T_{\\text{outside}} \).
2. Multiply the U-value by the area to get \( U A \).
3. Multiply that result by \( \\Delta T \) to get \( Q \).

Worked example

Problem. A wall has a U-value of \( 1.5 \), an area of \( 12 \) \( \\text{m}^2 \), and a temperature difference of \( 8 \) \( \\degree C \). Find the heat load.

1. Use \( Q = U A \\Delta T \).
2. Substitute the values, \( Q = 1.5 \\times 12 \\times 8 \).
3. Compute \( Q = 144 \).

Tips and common mistakes

• Make sure the temperature difference is positive, since the formula uses the size of the difference.
• Check that the area units match the U-value units, so the result comes out in the correct heat flow units.

Frequently asked questions