TOOL GUIDE
Insulation & condensation check
Check insulation outer-surface temperature against dew point and thickness requirements.
Purpose & scope
Check insulation outer-surface temperature against dew point and thickness requirements.
Steady one-dimensional model; flat faces for rectangular ducts. Corners, thermal bridges, gaps and vapour-barrier quality are excluded.
Inputs
Use drawings, design conditions and manufacturer data. Units and example values follow the calculator; example values are not universal design requirements.
| Parameter | Value / interpretation |
|---|---|
| Ambient temperature · °C | Air temperature outside the insulation at the installation location. |
| Ambient relative humidity · % | Ambient relative humidity used to calculate dew point. |
| Margin above dew point · K | Required surface-temperature margin above dew point, in K. |
| Application | Water pipe / Air duct / Refrigerant pipe |
| Cross-section | Round / Rectangular |
| Insulation material | Custom material / Elastomeric foam · ArmaFlex ACE Plus / PE · Tubolit Tubes / Glass wool · Knauf Duct Wrap / Stone wool · ROCKWOOL |
| Quick thickness | Custom |
| Duct width · mm | Rectangular duct width before insulation. |
| Duct height · mm | Rectangular duct height before insulation. |
| AC system | Residential / Commercial / VRV / VRF |
| Refrigerant line | Vapour / gas line / Liquid line |
| Copper outside diameter | Custom / 1/4 inch · 6.35 mm / 3/8 inch · 9.525 mm / 1/2 inch · 12.7 mm / 5/8 inch · 15.875 mm / 3/4 inch · 19.05 mm / 7/8 inch · 22.225 mm / 1 1/8 inch · 28.575 mm / 1 3/8 inch · 34.925 mm / 1 5/8 inch · 41.275 mm / 2 1/8 inch · 53.975 mm |
| Manufacturer minimum thickness · mm | 0 = manufacturer requirement not entered. Not inferred from system type. |
| Pipe outer surface temperature under insulation · °C | Outer pipe surface temperature beneath insulation, not automatically fluid temperature. |
| Pipe outside diameter · mm | Outside diameter for insulation; internal diameter for fluid flow. |
| Pipe length · m | Actual section length; include both supply and return where required. |
| Material thermal conductivity (λ) · W/(m·K) | Material thermal conductivity λ at operating temperature, in W/(m·K). |
| Combined external surface coefficient · W/(m²·K) | Combined outside surface heat-transfer coefficient; check convection/radiation conditions. |
| Thickness to check · mm | Insulation thickness to check. |
Steps
- Choose water pipe, duct or refrigerant pipe and round/rectangular geometry.
- Enter ambient conditions, pipe surface temperature, λ, h and thickness; for refrigerant lines enter manufacturer minimum.
- Compare surface temperature to dew point plus margin, save the alternative and verify actual construction.
Worked example
This reproducible training example uses the values below. Select the appropriate mode and overwrite restored project values. Example rates, K values and equipment losses are assumptions, not mandatory design criteria.
Examples use a decimal point and no thousands separator.
All example inputs
| Parameter | Value / interpretation |
|---|---|
| Ambient temperature | 30 °C |
| Ambient relative humidity | 75 % |
| Margin above dew point | 1 K |
| Application | Water pipe |
| Cross-section | Round |
| Insulation material | Custom material |
| Quick thickness | Custom |
| Duct width | 500 mm |
| Duct height | 300 mm |
| AC system | Residential |
| Refrigerant line | Vapour / gas line |
| Copper outside diameter | Custom |
| Manufacturer minimum thickness | 0 mm |
| Pipe outer surface temperature under insulation | 7 °C |
| Pipe outside diameter | 114.3 mm |
| Pipe length | 10 m |
| Material thermal conductivity (λ) | 0.035 W/(m·K) |
| Combined external surface coefficient | 8 W/(m²·K) |
| Thickness to check | 19 mm |
Expected results (rounded)
| Parameter | Value / interpretation |
|---|---|
| Dew point | 25.08 °C |
| Insulation outer surface temperature | 26.16 °C |
| Surface-temperature minimum thickness | 18.57 mm |
| Entered thickness | Meets entered targets |
Small differences in displayed rounding are normal. A result that passes the entered limits does not establish suitability for the complete system.
Method & limitations
Steady one-dimensional model; flat faces for rectangular ducts. Corners, thermal bridges, gaps and vapour-barrier quality are excluded.
Steady radial heat transfer through one insulation layer: R conduction = ln(r₂/r₁)/(2πλ), R outside = 1/(h·2πr₂). Enter an h that includes convection and equivalent radiation.
Condensation target: surface temperature ≥ dew point + margin. If the target is at or above ambient for a cold pipe, no finite thickness meets it.
Known pipe surface temperature, constant conductivity and surface coefficient. Supports, valves, vapor barriers, moisture ingress and multilayer construction are excluded. Verify sample values against materials and installation conditions.
Rectangular ducts: flat-face estimate with R = t/λ + 1/h, q = P·(ambient − bare surface temperature)/R, P = 2·(width + height). Corners, thermal bridges and outer-area changes are excluded; the face result is not the minimum corner temperature.
Common mistakes
Using internal instead of outside diameter; assuming fluid and pipe surface temperatures match; treating a condensation pass as manufacturer/fire compliance.
Projects & reports
- Choose or create an engineering project and enter your actual design inputs.
- Project inputs/results are autosaved in this browser. Where a saved-list panel is available, name and add the selected section or alternative to compare multiple options.
- Review the report before exporting PDF. In the print dialog select Save as PDF. Export JSON for backup and use Open file to restore it; PDF cannot restore project data.
Saved results do not automatically recalculate when another tool changes. Review any dependency warning, recalculate and update the affected results.
References & related tools
ASHRAE — Insulation for Mechanical Systems
The tool implements the methods and limits stated above; linking a standard does not establish complete compliance with that standard.