Duct Insulation R-Value Calculator
Heat gain or loss through duct insulation.
Enter your values
Enter the duct diameter in in.
Enter the duct length in ft.
Enter the insulation r-value you are working with.
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.
- Surface area
- 188.5 sq ft
- Heat transfer
- 1,100 BTU/h
- At R-8 instead
- 825 BTU/h
- Annual energy (2000 h)
- 645 kWh equivalent
- Temperature drop over run
- 2.55 °F at 400 CFM
Quick answer
Duct heat transfer equals surface area times the temperature difference divided by the insulation R-value.
BTU/h = area x ΔT / R
At a glance
| What it does | Heat gain or loss through duct insulation. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Duct diameter, Duct length, Insulation R-value, Temperature difference |
| Main output | Surface area |
| Formula | BTU/h = area x ΔT / R |
| Cost | Free — no sign-up, no download |
How to use the Duct Insulation R-Value Calculator
- 1Measure duct diameter and the length running through unconditioned space.
- 2Enter the current insulation R-value and the temperature difference.
- 3Compare against R-8 to see whether upgrading pays.
Inputs explained
- Duct diameter(in)
- Enter the duct diameter in in.
- Duct length(ft)
- Enter the duct length in ft.
- Insulation R-value
- Enter the insulation r-value you are working with.
- Temperature difference(°F)
- Enter the temperature difference in °F.
Worked example
Using the values the calculator loads with:
Inputs
- Duct diameter12 in
- Duct length60 ft
- Insulation R-value6
- Temperature difference35 °F
Results
- Surface area188.5 sq ft
- Heat transfer1,100 BTU/h
- At R-8 instead825 BTU/h
- Annual energy (2000 h)645 kWh equivalent
- Temperature drop over run2.55 °F at 400 CFM
Frequently asked questions
Minimum R-value?
Codes typically require R-6 in unconditioned space and R-8 in attics.
Does the vapour barrier matter?
Critically — without a sealed outer jacket, humid air condenses inside the insulation and ruins it.
What do I need to enter into the Duct Insulation R-Value 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 R-Value Calculator work out the answer?
Duct heat transfer equals surface area times the temperature difference divided by the insulation R-value. It applies the formula BTU/h = area x ΔT / R and shows the working so you can check each step by hand.
Is the Duct Insulation R-Value 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.