Duct Insulation Calculator

Calculator Inputs

Duct Shape

Duct Length (m)

Insulation Thickness (mm)

Width (m)

Height (m)

Diameter (m)

Thermal Conductivity k (W/m·K)

Duct Air Temperature (°C)

Ambient Temperature (°C)

Outer Film Coefficient h (W/m²·K)

Operating Hours per Day

Operating Days per Year

Energy Cost per kWh

System Efficiency

Results appear above this form after submission.

Example Data Table

Scenario	Shape	Length (m)	Size	Insulation (mm)	k Value	Duct Temp (°C)	Ambient Temp (°C)
Office Supply Duct	Rectangular	12	0.60 × 0.40 m	50	0.035	16	32
Process Exhaust Duct	Circular	18	0.55 m diameter	40	0.040	55	28
Warehouse Return Duct	Rectangular	20	0.80 × 0.50 m	75	0.036	20	38

Formula Used

1) Bare duct heat transfer: Q = ΔT / R_out

2) External convection resistance: R_out = 1 / (h × A)

3) Rectangular insulation conduction: R_cond = t / (k × A_avg)

4) Circular insulation conduction: R_cond = ln(r₂/r₁) / (2πkL)

5) Insulated heat transfer: Q_ins = ΔT / (R_cond + R_out,ins)

6) Heat saved: Q_saved = Q_bare − Q_ins

7) Annual energy saved: (Q_saved × hours/day × days/year) / (1000 × efficiency)

This calculator uses steady-state one-dimensional conduction and outside convection. It is suitable for fast engineering estimates, comparison studies, and insulation screening.

How to Use This Calculator

Select rectangular or circular duct geometry.
Enter the duct length and the correct size dimensions.
Provide insulation thickness in millimeters.
Enter the insulation thermal conductivity value.
Input duct air temperature and surrounding ambient temperature.
Set the external film coefficient for the installed condition.
Add operating schedule, energy cost, and system efficiency.
Press calculate to see heat loss, savings, and annual impact.

FAQs

1. What does this duct insulation calculator estimate?

It estimates bare and insulated heat transfer, heat reduction percentage, outer surface temperature, insulation volume, annual energy savings, and estimated cost savings.

2. Can I use it for both hot and cold ducts?

Yes. The calculator uses the absolute temperature difference between duct air and ambient air, so it works for chilled ducts and heated ducts.

3. Why is thermal conductivity important?

Thermal conductivity controls how easily heat passes through insulation. Lower k-values usually mean better insulating performance and lower heat transfer.

4. What is the outside film coefficient?

It represents convective heat transfer between the insulation surface and surrounding air. Wind, airflow, and installation conditions affect this value.

5. Is the result exact for field installations?

No. It is an engineering estimate. Real installations may include thermal bridges, joints, hangers, moisture effects, and variable airflow conditions.

6. Why does the chart change with insulation thickness?

Increasing insulation thickness raises thermal resistance, which reduces heat flow. The plotted curve helps visualize diminishing returns as thickness increases.

7. What units should I enter?

Use meters for size and length, millimeters for insulation thickness, degrees Celsius for temperatures, W/m·K for conductivity, and W/m²·K for film coefficient.

8. Can this help compare insulation options?

Yes. Change thickness, conductivity, or schedule values to compare performance, savings, and material volume across multiple design alternatives.