Pipe Insulation Thickness
Required thickness from cylindrical conduction at a target surface temp.
Example
You enter
- Pipe OD (in) 1
- Pipe surface (°F) 250
- Ambient (°F) 75
- Outer surface limit (°F) 120
- Insulation k (BTU*in/hr*ft²*F) 0.27
You get
- Required thickness 0.364
- R2 (in) 0.864
- R1 (in) 0.5
Checked against published worked examples from: PDHonline (PDH Center).
Details, formula, and sources
Formula or tableHeat loss through pipe insulation: Q = 2π × (k/12) × L × ΔT / ln(r2/r1) per foot of pipe, k per inch of thickness (BTU-in/hr-ft²-°F), balanced against the outer film h × (2π r2/12) × (T_surface − T_ambient) and solved for r2. Hot-surface (touch-limit) case only; condensation is a separate tile (pipe-insulation-for-condensation).
Source and editionASHRAE Fundamentals by name; ASTM C680 for surface-condition calculation.
Free accessASTM C680 licensed; principles free in published engineering texts.
What governsEstimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
API field namespipe_od_in, surface_temp_F, ambient_F, surface_limit_F, k_btu_in_per_hr_ft2_F, thickness_in, r2_in, r1_in
- Insulation k-value entered from the insulation data sheet (about 0.27 for mineral fiber at mean temperature)manufacturer + public engineering reference
- Outside-film coefficient 1.65 BTU/(hr × ft² × °F) horizontal pipe, entered; or computed (added 2026-10-09) at the jacket OD and target surface temperature from Churchill-Chu natural convection, gray-body radiation at the jacket emissivity and Churchill-Bernstein wind convectionengineering practice; bare-pipe-heat-loss