Skip to main content

Find your next tool

DashboardAndroid app
Language
Appearance

Plant Engineering Calculator

Updated Sep 17, 2026

Boiler Economizer Savings Calculator — Flue Heat Recovery & Fuel Savings

Estimate recoverable economizer duty, equivalent fuel input reduction and annual fuel-cost savings from feedwater temperature rise.

Live calculationWorking shownPrivate in browser

Inputs

Results

Recovered duty 581.4 kW
Equivalent fuel input 684.0 kW
Annual fuel energy 4103.9 MWh
Annual fuel savings $143637
More actions

Shared links reopen these inputs. Recent and saved calculations stay in this browser unless you clear site data.

Formula

Q=mfw·Cp·ΔT/3600; fuel saved=Q/η.

Your calculation, step by step

These steps use the values currently entered above so the result can be checked independently.

  1. 1.Recovered duty = 20000 × 4.186 × 25.0 ÷ 3600 = 581.4 kW.
  2. 2.Fuel input avoided = 581.4 ÷ 0.850 = 684.0 kW.
  3. 3.Annual saving = 4103.9 MWh × $35.00/MWh = $143637.

How to use this calculator

  1. Enter measured or design values using the units shown beside each field.
  2. Review the live results and the substituted calculation steps before using the estimate.
  3. Check the assumptions below, then continue to a related calculator when the next engineering decision needs another model.

Worked example

20,000 kg/h feedwater heated by 25 K at Cp=4.186 recovers about 581 kW before boiler-efficiency conversion.

Assumptions and limits

  • Uses sensible feedwater heating only.
  • Verify stack-temperature, corrosion/dew-point and economizer pressure-drop limits.

How to interpret the result

Treat the primary result as an engineering screening value, then use the secondary outputs to understand scale, energy or operating impact. Confirm site measurements, equipment limits and applicable standards before making a design or control change.

Questions engineers ask

How does an economizer reduce boiler fuel use?

Recovered flue-gas heat raises feedwater temperature before it reaches the boiler, reducing the burner input needed to reach the same steam output.

Why is boiler efficiency used after calculating recovered heat?

Recovered feedwater duty is useful heat. Dividing by the applicable boiler efficiency estimates the larger fuel-input reduction that would otherwise have been required to supply that useful heat.

Can I keep lowering stack temperature to increase savings?

No. Practical recovery is constrained by acid or water dew point, corrosion risk, fouling, draft and pressure-drop limits. Verify the allowable stack condition for the actual fuel and equipment.

Continue the calculation

Use the next calculator in the same engineering workflow instead of restarting from search.

boiler feedwater heating dutyboiler stack lossboiler efficiency
Methodology. MAXScanner shows the governing formula, entered values and calculation outputs so the estimate is auditable. The calculator is a screening aid; assumptions and equipment-specific limits remain part of the engineering review.