Insulated Pipe Heat Loss (Radial)
Radial (cylindrical) conduction heat loss per linear foot and total through pipe insulation via the log-mean form.
Example
You enter
- Pipe outer diameter (in) 2
- Insulation thickness (in) 1
- Insulation k-value (BTU-in/hr-ft2-F) 0.25
- Fluid / surface temperature (°F) 200
- Ambient temperature (°F) 70
- Pipe length (ft) 1
You get
- Heat loss per linear foot 24.6 BTU/hr-ft
- Total heat loss 24.6 BTU/hr
Checked against published worked examples from: Fourier cylindrical-shell conduction + ASTM C335 k-values.
Details, formula, and sources
ScopeFrom outer diameter, insulation thickness and k-value, and the temperature difference.
Formula or tableQ/L = (T_hot - T_amb) / (ln(r2/r1)/(2 pi k') + 1/(2 pi r2 h)), where r1 = OD/2, r2 = r1 + thickness, k' = k_value / 12 converts BTU-in/(hr.ft2.F) to BTU/(hr.ft.F), and the film term is dropped when no outer film coefficient h is entered (Q/L = 2 pi k' dT / ln(r2/r1)); jacket temperature = T_amb + (Q/L)/(2 pi r2 h).
Source and editionFourier conduction through a cylindrical shell (public heat-transfer formula); insulation k-values per ASHRAE Fundamentals / ASTM C335, by name.
Free accessFree principles in published HVAC texts; k-values user-supplied.
What governsEstimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
API field namesod_in, thickness_in, k_value, hot_f, amb_f, length_ft, q_per_ft_btuh, q_total_btuh
- k at mean temperature insulation conductivity rises with temperature; the value entered is at the mean insulation temperatureASTM C335
- Outer film optional; without it the jacket is taken at ambient (conservative). About 1.5-2.5 BTU/hr-sq ft-F in still air for a painted or canvas jacket (added 2026-10-09); or computed from the bare-pipe-heat-loss model (Churchill-Chu, gray-body radiation, Churchill-Bernstein wind) at the jacket OD, iterated with the jacket temperatureASHRAE Fundamentals; bare-pipe-heat-loss