Select your calculation route and enter reliable inputs. See duty, flow, and transfer checks instantly. Download CSV or PDF for clean project documentation always.
| Case | Method | Key Inputs | Base Duty (kW) | Notes |
|---|---|---|---|---|
| 1 | Sensible | m=1.2 kg/s, Cp=3.9, ΔT=18°C | 84.24 | Hot water loop heating. |
| 2 | Sensible | m=0.8 kg/s, Cp=2.2, ΔT=25°C | 44.00 | Oil preheating stage. |
| 3 | Latent | m=0.05 kg/s, hfg=2257 kJ/kg | 112.85 | Steam condensation duty. |
| 4 | Exchanger | U=750, A=18, LMTD≈22K | 297.00 | Plate exchanger estimate. |
| 5 | Combined | Sensible + Latent (two blocks) | 197.09 | Mixed heating with phase change. |
Heat duty for temperature change without phase change:
Q = m · Cp · ΔT
Heat duty for phase change at near-constant temperature:
Q = m · hfg
Heat duty based on overall transfer:
Q = U · A · LMTD
For counterflow LMTD:
ΔT1 = Th,in − Tc,out
ΔT2 = Th,out − Tc,in
LMTD = (ΔT1 − ΔT2) / ln(ΔT1 / ΔT2)
Required input duty includes allowances:
Qreq = Qbase / η · Ffoul · Fsafe
Heat duty is the baseline for sizing heaters, boilers, coils, and exchanger packages on construction and commissioning work for fast field decisions today. It supports curing enclosures, temporary hydronic loops, process skid tie‑ins, and HVAC startup loads. A documented duty estimate reduces temperature instability, rework, and schedule risk. This calculator lets you choose the physics that fits the job and keeps assumptions transparent for reviewers and clients.
Use the sensible route when fluid temperature changes without phase change. Examples include warming water or glycol, preheating fuel oil, or raising wash-down temperature. Enter mass flow, specific heat, and temperature change. The tool converts between SI and Imperial inputs and reports duty in kW and BTU/hr. Apply efficiency, fouling, and safety multipliers to represent real equipment performance and site variability.
Use the latent route when evaporation, condensation, or melting dominates the load. Steam coils, drying operations, humidification, and condensate recovery frequently require latent accounting. Provide the phase-change flow and an appropriate latent heat value for the operating condition. Because latent loads can be large, confirm property data and apply conservative allowances for accurate duty budgeting early. Combined mode allows sensible and latent contributions to be added for mixed processes.
The exchanger route provides a quick check for preliminary exchanger sizing or vendor validation. Enter overall coefficient, area, and four terminal temperatures for counterflow LMTD. Keep ΔT1 and ΔT2 with the same sign; opposite signs indicate inconsistent temperatures. When approaches are close, LMTD trends toward the arithmetic mean. Multiply for fouling to represent scaling, dirt, and imperfect surfaces during construction and startup.
After results are shown, compare required duty against available utilities, fuel limits, and electrical capacity. Switch to hourly or daily energy outputs to estimate operating cost and fuel logistics. Verify turndown and control stability for packaged heaters at part load. For exchanger systems, confirm outlet temperatures against material limits and safety requirements and coordination with other trades. Export CSV or PDF to maintain traceable documentation for submittals and change management.
Heat duty is the thermal rate needed to heat or cool a stream or system. The calculator reports required duty after applying efficiency, fouling, and safety multipliers, using the selected method for sensible, latent, or exchanger-based estimates.
Use it when the material only changes temperature and does not change phase. Enter mass flow, specific heat, and temperature difference. This approach is common for hydronic loops, glycol circuits, and fluid preheating.
Latent heat dominates during evaporation, condensation, freezing, or melting. If steam condenses in a coil, or moisture is removed by evaporation, include phase-change flow and latent heat for a realistic duty estimate.
LMTD becomes invalid if the two terminal temperature differences have opposite signs, which indicates inconsistent inlet or outlet temperatures. Recheck hot and cold stream temperatures so both ΔT1 and ΔT2 remain positive or negative.
Efficiency below 1.0 increases required input duty because more energy is needed to deliver the same useful heat. Fouling and safety multipliers increase duty to cover degraded surfaces, uncertainty, and operating margin.
Yes. Choose hourly or daily basis to convert duty into energy. Combine that with fuel or electricity rates and equipment efficiency to estimate operating cost and support temporary utility planning.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.