Duct Heat Loss Calculator
Estimate conductive heat loss from a round duct, equivalent monthly energy and cost using editable duct length, diameter, temperature difference, insulation value and operating schedule.
Default project preview
1,152 BTU/h
Duct surface area
157.1 ft²
Thermal transfer
338 W
Equivalent system input
0.38 kW
Monthly energy
90 kWh
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Round-duct surface area = π × diameter × length. Conductive heat transfer = area × temperature difference ÷ insulation resistance, adjusted by the entered installation allowance.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Duct Heat Loss Calculator questions
Does this include duct leakage?+
No. Leakage is a separate air-loss mechanism and should be evaluated independently.
Why does duct location matter?+
The temperature difference between duct air and surrounding space drives conductive heat transfer.
Can this size duct insulation?+
It compares entered insulation values but does not determine condensation control or required insulation.