Calculator
Example data table
Sample scenarios for quick reference (planning estimates).
| Steam flow (kg/h) | Blowdown (%) | Losses (% of steam) | Condensate return (%) | Feedwater with margin (kg/h) | Makeup water (kg/h) |
|---|---|---|---|---|---|
| 5,000 | 3 (of steam) | 0.5 | 70 | 5,456 | 1,637 |
| 8,000 | 5 (of feedwater) | 1.0 | 60 | 9,544 | 3,818 |
| 12,000 | 2 (of steam) | 0.3 | 80 | 12,745 | 2,196 |
Formula used
- Steam from duty (optional): Steam (kg/h) = (Duty(kW) × 3600) ÷ Δh(kJ/kg).
- If duty is fuel input: Steam duty = Fuel duty × Efficiency.
- Blowdown, percent of steam: Blowdown = Steam × (BD% ÷ 100).
- Blowdown, percent of feedwater: Feedwater = Steam ÷ (1 − BD%).
- Losses: either Steam × Loss% or a fixed flow value.
- Feedwater: Feedwater = Steam + Blowdown + Losses.
- Margin: Feedwater_with_margin = Feedwater × (1 + Safety%).
- Makeup water: Makeup = max(Feedwater_with_margin − Condensate, 0).
Δh is the enthalpy rise from feedwater to steam. Use project steam tables or equipment data when available.
How to use this calculator
- Select a calculation method based on available site data.
- Enter steam flow, or enter duty with efficiency and Δh.
- Set blowdown rate and choose the correct definition basis.
- Add losses for vents, sampling, leaks, or drains.
- Enter condensate return to estimate required makeup water.
- Add a safety factor for variability and design allowance.
- Press Calculate and download CSV or PDF reports.
Boiler feedwater flow planning guide
Boiler feedwater flow is the practical water supply rate required to sustain steam production while managing system losses and water-quality control. In construction and commissioning, this estimate supports pump sizing, deaerator selection, chemical dosing plans, and temporary utility planning. A good feedwater estimate also helps teams validate that storage volume and makeup water connections can maintain stable operation during peak loads and start-up transitions.
The starting point is steam demand. If you have measured or specified steam flow, the calculation is direct. If you only know thermal duty, the calculator converts duty to steam flow using an enthalpy rise (Δh) between feedwater and steam. This approach is widely used during design when the final operating conditions are still being refined. Once steam flow is known, the model adds blowdown and losses to determine total feedwater required.
Blowdown is essential for controlling dissolved solids and protecting heat-transfer surfaces. Because sites define blowdown differently, this calculator lets you choose whether the percentage is based on steam flow or on feedwater flow. Additional losses represent vents, sampling, leaks, warm-up drains, or intermittent operating practices that can be significant during early operation. Finally, condensate return reduces makeup water demand and improves overall efficiency, but it can vary with system cleanliness, trap performance, and operational discipline.
For field teams, pair the calculated rates with instrument checks: verify feedwater flowmeter range, level control valve capacity, and deaerator venting. Small control issues can mimic “missing” condensate and distort early measurements.
Example scenario: A temporary boiler package supports a curing enclosure and testing loads. Enter a steam flow of 5,000 kg/h, blowdown 3% (of steam), losses 0.5% (of steam), condensate return 70% (of steam), and a 5% safety factor. The calculator reports approximately 5,456 kg/h feedwater with margin and about 1,637 kg/h makeup water. If condensate return drops to 50%, makeup water increases materially, which may require a larger storage tank or a more reliable supply connection.
Use the results to confirm equipment capacities and to create clear field documentation. For pumps, compare the feedwater-with-margin value to available pump curves at expected suction conditions. For water supply, compare makeup water to available municipal, well, or temporary storage capabilities. If the project includes staged commissioning, run multiple scenarios for warm-up, steady operation, and peak testing. Saving a CSV or PDF report per scenario supports approvals and reduces disputes during handover.
Reminder: Treat this as a planning estimate. Verify final settings with vendor data, steam tables, water treatment targets, and site-specific operating procedures.
FAQs
1) What is boiler feedwater flow?
It is the total water rate entering the boiler system to support steam production, including blowdown and other losses. It is often higher than steam flow because some water exits as blowdown or drains.
2) Why can feedwater be higher than steam flow?
Boilers discharge blowdown to control water chemistry, and real systems have vents, sampling, and leakage. Those outflows must be replaced, so feedwater includes steam flow plus these additional demands.
3) How do I choose the blowdown basis?
Use the basis that matches how your site or vendor specifies blowdown. If documentation says “% of steam,” select that. If it states “% of feedwater,” choose the feedwater basis option.
4) What should I enter for enthalpy rise (Δh)?
Use steam table or vendor values for your pressure and temperature. Δh is the energy per kilogram needed to turn feedwater into steam. Typical planning values are often around 1,800–2,400 kJ/kg, depending on conditions.
5) How does condensate return affect makeup water?
Condensate return offsets the required makeup water. Higher return reduces treatment chemicals and water consumption. Lower return increases makeup demand and may require larger storage, higher supply capacity, or operational changes.
6) What safety factor is reasonable?
For early planning, 3–10% is common to cover load swings, unknown losses, and instrument uncertainty. Use a higher factor if operations are intermittent, traps are unverified, or condensate return is expected to vary.
7) Why do my results look inconsistent?
Most issues come from mixed units or an incorrect basis selection. Confirm steam units, fixed-flow units, and whether percentages are based on steam or feedwater. Also ensure condensate return does not exceed calculated feedwater.