Pipe Insulation Heat Loss (bare vs insulated)
Cylindrical conduction + convection + radiation; effectiveness % vs bare.
Example
You enter
- Pipe OD (in) 2.375
- Pipe surface T (°F) 200
- Ambient T (°F) 70
- Insulation type fiberglass
- Thickness (in) 1.5
- Jacket emissivity (0-1) 0.9
You get
- Q bare 124.3 BTU/hr·ft
- Q insulated 22.4 BTU/hr·ft
- Effectiveness 82.0 %
Details, formula, and sources
Six insulation k-values with manufacturer attribution.
R_cond = ln(r2/r1) / (2π × k); h_outside = h_conv(V) + h_rad(eps, T); R_outside = 1 / (h_outside × 2π × r2); Q = (T_s − T_a) / (R_cond + R_outside). h_conv ≈ 0.225 + 0.000625 × V_fpm (engineering approximation); h_rad = eps × σ × ((T_s_R² + T_a_R²)(T_s_R + T_a_R)). Iterate for outer-surface temperature.
ASHRAE Handbook Fundamentals chapter 25 (insulation) by name; ASTM C680 (cylindrical surface conditions) by name; manufacturer k-values from data/hvac/insulation-k-values.json.
ASTM C680 licensed; manufacturer technical bulletins free at each manufacturer site.
Estimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
Field names used by the API: pipe_OD_in, surface_T_F, ambient_T_F, insulation, thickness_in, jacket_emissivity, Q_bare_BTU_hr_ft, Q_insulated_BTU_hr_ft, effectiveness_pct
- Stefan-Boltzmann constant σ 0.1714×10⁻⁸ BTU/(hr·ft²·°R⁴)physical fact
- Default jacket emissivity 0.9 (painted steel / fabric jacket)engineering practice
- Iterative outer-surface T solve 12 fixed-point iterations for the R_outside ↔ T_s2 couplingengineering practice