Duct Insulation Heat Loss Calculator
Heat loss through duct insulation.
Enter your values
Enter the duct diameter in in.
Enter the duct length in ft.
Enter the insulation r-value in R.
Enter the temperature difference in °F.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Duct surface area
- 78.5 sq ft
- Heat loss/gain
- 524 BTU/hr
- Loss per linear foot
- 17.5 BTU/hr/ft
Quick answer
Heat loss through duct insulation follows Q = A x ΔT / R, using the duct's outer surface area and the insulation R-value.
Q (BTU/hr) = surface area x ΔT / R-value
At a glance
| What it does | Heat loss through duct insulation. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Duct diameter, Duct length, Insulation R-value, Temperature difference |
| Main output | Duct surface area |
| Formula | Q (BTU/hr) = surface area x ΔT / R-value |
| Cost | Free — no sign-up, no download |
How to use the Duct Insulation Heat Loss Calculator
- 1Enter the duct diameter and length to get the surface area.
- 2Use the insulation's rated R-value (R-6 and R-8 are common attic duct wraps).
- 3Multiply by the temperature difference between the duct air and surrounding space, divided by R-value.
Inputs explained
- Duct diameter(in)
- Enter the duct diameter in in.
- Duct length(ft)
- Enter the duct length in ft.
- Insulation R-value(R)
- Enter the insulation r-value in R.
- Temperature difference(°F)
- Enter the temperature difference in °F.
Worked example
Using the values the calculator loads with:
Inputs
- Duct diameter10 in
- Duct length30 ft
- Insulation R-value6 R
- Temperature difference40 °F
Results
- Duct surface area78.5 sq ft
- Heat loss/gain524 BTU/hr
- Loss per linear foot17.5 BTU/hr/ft
Frequently asked questions
Why insulate ducts in attics?
Uninsulated ducts in unconditioned attics can lose 20-30% of delivered heating or cooling capacity.
Is higher R-value always better?
Yes for efficiency, though returns diminish; R-6 to R-8 is standard for most attic and crawlspace duct runs.
What do I need to enter into the Duct Insulation Heat Loss Calculator?
Just 4 values: duct diameter, duct length, insulation r-value, temperature difference. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Duct Insulation Heat Loss Calculator work out the answer?
Heat loss through duct insulation follows Q = A x ΔT / R, using the duct's outer surface area and the insulation R-value. It applies the formula Q (BTU/hr) = surface area x ΔT / R-value and shows the working so you can check each step by hand.
Is the Duct Insulation Heat Loss Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.