Duct Heat Gain Calculator

Duct Heat Gain Formula:

\[ Q_{heat\ gain} = U_{overall} \times SA_{Duct} \times \Delta T \]

Overall Heat Transfer Coefficient:

W/m²·K

Surface Area of Duct:

m²

Temperature Change (Outdoor - Inside):

Duct Heat Gain:

1. What is a Duct Heat Gain Calculator?

Definition: This calculator estimates the amount of heat gained or lost through ductwork based on thermal properties and temperature differences.

Purpose: It helps HVAC engineers and technicians determine thermal loads and energy efficiency in duct systems.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ Q_{heat\ gain} = U_{overall} \times SA_{Duct} \times \Delta T \]

Where:

\( Q_{heat\ gain} \) — Heat gain through duct walls (Watts)
\( U_{overall} \) — Overall heat transfer coefficient (W/m²·K)
\( SA_{Duct} \) — Surface area of duct (m²)
\( \Delta T \) — Temperature difference between outdoor and inside air (K)

Explanation: The formula calculates heat transfer through the duct walls based on thermal properties and temperature differential.

3. Importance of Duct Heat Gain Calculation

Details: Accurate heat gain calculations are essential for proper HVAC system sizing, energy efficiency, and preventing condensation issues.

4. Using the Calculator

Tips: Enter the overall heat transfer coefficient (default 0.25 W/m²·K), duct surface area, and temperature difference. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical U-value for ductwork?
A: Uninsulated sheet metal ducts typically have U-values of 5-6 W/m²·K, while insulated ducts range from 0.2-1.0 W/m²·K.

Q2: How do I measure duct surface area?
A: Calculate perimeter × length for rectangular ducts or π × diameter × length for round ducts.

Q3: Why use Kelvin for temperature difference?
A: Kelvin is used because it represents absolute temperature differences, avoiding negative values in calculations.

Q4: Does this account for air leakage?
A: No, this only calculates conductive heat transfer through duct walls. Air leakage requires separate calculations.

Q5: How accurate are these calculations?
A: Results are theoretical estimates. Actual performance may vary ±5% due to installation factors and material variations.