formula.expertYour record

Boiler Blowdown Percent

%B=TDSfwTDSb×100\%B = \frac{\text{TDS}_{fw}}{\text{TDS}_b} \times 100
sig figs

Worked example: 100 ppm feedwater, 3000 ppm limit → 3.33% blowdown. Press Try an example to run it live, then adjust anything.

Enter your known values, leave one input blank, and solves for the missing one. Tap a variable’s symbol to see what it means, with a typical value. Change any unit and the answer follows.

Where Boiler Blowdown Percent fits

In this toolkit

See also

Boiler Cycles of Concentration: Both use feedwater TDS and boiler water TDS limit.
Here the solver did the work. Could you?

Boiler cycles →

UniversityProcess & Water Chemistry

Test your skills in the Exam Room: new numbers every attempt. Free lessons for students, no sign-up, just pure learning.

See your Report Card
Learning zone

Boiler Blowdown Percent explained

TDSfwTDSb%B

Blowdown percentage is the reciprocal of cycles wearing a different hat: if the drum may hold 3000 ppm and the feedwater carries 100 ppm, you must dump 100/3000 = 3.3% of the feedwater to keep the solids in balance. It is the number a plant engineer actually budgets, because blowdown leaves at saturation temperature and takes its enthalpy with it: every percent of continuous blowdown on a 100 psig boiler costs roughly 0.2–0.3% of fuel.

The lever that pays is the feedwater, and the biggest single term in feedwater TDS is usually makeup rather than condensate. Raise condensate return from 50% to 80% and the feedwater TDS falls by more than half, and the blowdown percentage falls with it: fuel, water, chemical and sewer savings all at once. Two field cautions: measure boiler TDS on a cooled, depressurised sample or the flashing will concentrate it and read high, and do not confuse continuous surface blowdown, which controls TDS, with the bottom blowdown that clears sludge from the mud drum. Only the surface blowdown belongs in this equation.

Boiler Blowdown Percent formula

%B=TDSfwTDSb×100\%B = \frac{\text{TDS}_{fw}}{\text{TDS}_b} \times 100
Where
  • %B\%B= Blowdown percent of feedwater (%)
  • TDSfw\text{TDS}_{fw}= Feedwater TDS (mg/L)
  • TDSb\text{TDS}_b= Boiler water TDS limit (mg/L)
Where this comes from

Worked from first principles: a definition, a balance or unit arithmetic, so it needs no outside source.

In this toolkit

The boiler water balance

8 formulasBoiler cycles, blowdown percent and rate, condensate return, makeup, flash steam and boiler horsepower — the steam side's water balance.

Revised 16 October 2026
Cite this page

formula.expert. (2026, October 16). Boiler Blowdown Percent Formula & Calculator. https://formula.expert/solvers/boiler-blowdown-percent

formula.experthttps://formula.expert/solvers/boiler-blowdown-percent