Hot Water Heat Loss Calculator

Calculate heat loss from hot water pipes or storage tanks based on temperature difference, insulation, and geometry.

System Type

Hot Water Temperature (°C)

Ambient Temperature (°C)

Pipe Length (m)

Pipe Inner Diameter (mm)

Pipe Outer Diameter (mm)

Insulation Thickness (mm) (0 = uninsulated)

Insulation Thermal Conductivity (W/m·K)

Inner Surface Heat Transfer Coefficient (W/m²·K)

Outer Surface Heat Transfer Coefficient (W/m²·K)

Pipe/Tank Wall Thermal Conductivity (W/m·K) Steel ≈ 50, Copper ≈ 385, Plastic ≈ 0.4

Duration (hours)

Results will appear here.

Pipe (Cylindrical Geometry) — Fourier's Law for radial conduction:

Q = ΔT / R_total

R_total = 1/(h_i·2πr₁L) + ln(r₂/r₁)/(2πk_wallL) + ln(r₃/r₂)/(2πk_insL) + 1/(h_o·2πr₃L)

Where: r₁ = inner radius, r₂ = outer pipe radius, r₃ = outer insulation radius, L = pipe length

Tank (Flat-Wall / Planar Geometry):

Q = ΔT / R_total

R_total = 1/(h_i·A) + t_wall/(k_wall·A) + t_ins/(k_ins·A) + 1/(h_o·A)

Auto surface area (spherical): A = 4π·(3V/4π)^2/3

Tank temperature drop: ΔT_drop = Q·t / (m·c_p), where m = mass of water, c_p = 4186 J/(kg·K)

Total energy loss: E = Q × t (kWh)

Water density assumed as 1 kg/L for temperature drop calculation.
Specific heat of water: c_p = 4186 J/(kg·K) (Incropera & DeWitt, Fundamentals of Heat and Mass Transfer).
Tank wall thickness assumed 5 mm steel when using tank mode.
Auto tank surface area calculated assuming a spherical shape (minimum surface area for a given volume).
Pipe cylindrical resistance uses the standard logarithmic formula for radial conduction (ASHRAE Handbook — Fundamentals).
Inner convective coefficient h_i ≈ 300 W/m²·K is typical for turbulent water flow; h_o ≈ 10 W/m²·K for natural convection in air.
Insulation thermal conductivity: mineral wool ≈ 0.04 W/m·K, polyurethane foam ≈ 0.025 W/m·K (BS EN ISO 10211).
Steady-state heat loss is assumed (temperature of water does not change significantly during the period — valid for short durations or well-heated systems).
Reference: ISO 12241:2008 — Thermal insulation for building equipment and industrial installations.

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