Pipe Insulation for Condensation Control (Cold Lines)
The cold-pipe mirror of insulation-thickness, with the target COMPUTED instead of hand-entered.
Example
You enter
- Pipe OD (in) 1
- Cold-pipe surface temp (°F) 40
- Ambient dry-bulb (°F) 75
- Ambient RH (%, design-day) 50
- Insulation k (BTU-in/hr-ft²-F) 0.27
- Outside film coeff (BTU/hr-ft²-F) 1.65
You get
- Ambient dew point 55.1062 F
- Thickness (in) 0.11246
- R2 (in) 0.61246
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method.
Details, formula, and sources
ScopeThe ambient dew point from the design-day RH, then the minimum wall that holds the outer jacket exactly at it. A 1-in 40 F chilled line at 75 F / 50% RH needs 0.11 in - round UP to the next stock wall, because a jacket at the dew point is on the edge of sweating all day. Flags the no-risk case (pipe above dew point) and the near-saturation case no thickness fixes.
Formula or tableTdp from the ambient RH (saturation-vapor-pressure psychrometrics); minimum wall from the outer-surface balance h (2 pi r2/12)(Tamb - Tdp) = 2 pi (k/12) (Tdp - Tpipe)/ln(r2/r1), with k per inch, solved for r2; thickness = r2 - r1.
Source and editionStandard cylindrical-conduction and surface-film heat balance (the same public engineering relations as the landed insulation-thickness and pipe-heat-loss-radial tiles) with the dew point from the catalog's pinned psychrometric functions; no standard table reproduced.
Free accessThe conduction/film balance and Magnus-form psychrometrics are public engineering relations; manufacturer condensation-control design guides publish the equivalent tables free.
What governsEstimate. AHJ and licensed professional govern.
API field namespipe_od_in, pipe_temp_F, ambient_F, ambient_rh_pct, k_btu_in_per_hr_ft2_F, outside_film_coeff_btu_hr_ft2_F, dew_point_F, thickness_in, r2_in
- Dew point source computed from the repo's pinned saturation-vapor-pressure / dew-point functions, not a lookuppure-math.js psychrometrics (Magnus form)
- Film coefficient 1.65 BTU/hr-ft^2-F still-air default, identical to the insulation-thickness sibling; or computed (added 2026-10-09) from Churchill-Chu natural convection and gray-body radiation at the jacket emissivity, OD and dew-point surfacepublic engineering reference value; bare-pipe-heat-loss
- Vapor retarder assumed continuous; failure moves condensation inside the insulationmanufacturer design guides