About

In hydronic heating and district energy networks, Energy (Heat) is transported by water. Calculating the volume of water required to deliver a specific amount of heat is fundamental for sizing pumps, pipes, and control valves. Unlike basic calculators that assume a constant water density, this tool respects the laws of thermodynamics.

Water expands as it heats up, meaning 1 m³ of water at 90°C carries less mass - and therefore less heat energy - than at 40°C. This tool interpolates the specific density (ρ) and specific heat capacity (c) based on your average system temperature, providing the rigorous accuracy required for professional hydraulic balancing.

Formulas

The relationship between Heat Energy (Q), Mass (m), and Temperature Difference (ΔT) is:

Q = m ⋅ c ⋅ ΔT

Since we need Volume (V) and m = V ⋅ ρ:

V = Qc ⋅ ρ ⋅ (T_in − T_out)

Where:

Q = Energy (converted to kCal)
c = Specific Heat Capacity (≈ 1 kCal/kg°C)
ρ = Density of water at T_avg (kg/m³)

Reference Data

Temp (°C)	Density (kg/m³)	Volume for 1 Gcal (ΔT=20)
10	999.7	50.01 m³
40	992.2	50.39 m³
60	983.2	50.85 m³
80	971.8	51.45 m³
95	961.9	51.98 m³
110	951.0	52.57 m³
130	934.8	53.48 m³

Frequently Asked Questions

Delta T (ΔT) is the temperature difference between the Supply (Flow) pipe and the Return pipe. In standard heating systems, this is often designed as 20°C (e.g., 80/60 regime). A smaller Delta T requires more water volume to carry the same energy.

We need the average temperature ((Supply + Return) / 2) to determine the water density. Water at 90°C is significantly lighter than water at 40°C, which affects the volume calculation.

No. This tool is calibrated specifically for the properties of pure water. Glycol (antifreeze) has a lower specific heat capacity and different density, which would require a higher flow rate for the same energy transfer.

For quick estimates without density correction: Volume (m3) ≈ Gcal * 1000 / Delta T. For 1 Gcal and Delta T 20, Volume is roughly 50 m3.