Rating conversion
F&A 100 °C Converter
Indian boilers are quoted in kilograms per hour "from and at" 100 °C. It is a rating datum, not an operating condition, and reading it as actual output is the most common and most expensive mistake in an Indian boiler purchase. This converts between the two, in both directions.
Convert
The capacity figure on the quotation or nameplate.
Gauge pressure, not absolute.
After condensate return, deaerator and economiser. This is what moves the answer most.
Actual steam output
1,784kg/h
A 2,000 kg/h F&A boiler at these conditions
- Evaporation factor
- 1.1209
- Shortfall against nameplate
- 10.8%
- Equivalent boiler horsepower
- 128 BHP
Boiler horsepower is shown only because it appears on imported datasheets. It is not Indian practice and should not be used to specify equipment here.
What "from and at 100 °C" actually means
The F&A rating is the evaporation a boiler would achieve under one specific, artificial condition: feedwater entering at 100 °C, steam leaving at 100 °C, at atmospheric pressure. Under those conditions each kilogram of water absorbs exactly the latent heat of vaporisation, conventionally taken as 2256.9 kJ/kg.
Real boilers do not run like that. Feedwater arrives below 100 °C, so it has to be heated before it can boil at all, and steam leaves at working pressure, where it carries more energy than steam at atmospheric pressure. Both effects mean every real kilogram of steam absorbs more than 2256.9 kJ, so a boiler always evaporates less than its F&A rating.
The ratio between the two is the evaporation factor: the enthalpy of saturated steam at working pressure, minus the enthalpy of feedwater, divided by 2256.9. It is always greater than one for feedwater below 100 °C, and typically falls between 1.04 and 1.19 in ordinary industrial service.
F&A rating = actual evaporation × (h_g at working pressure − h_f at feedwater temperature) ÷ 2256.9
Evaporation factors
Multiply actual evaporation by the factor to get the F&A 100 °C rating; divide a quoted F&A rating by it to get real output. Computed from IAPWS-IF97 against a datum of 2256.9 kJ/kg.
| Working pressure | Feed 30 °C | Feed 60 °C | Feed 80 °C | Feed 100 °C |
|---|---|---|---|---|
| 3.50 kg/cm²(g) | 1.1594 | 1.1039 | 1.0668 | 1.0295 |
| 7.00 kg/cm²(g) | 1.1703 | 1.1147 | 1.0776 | 1.0404 |
| 10.54 kg/cm²(g) | 1.1764 | 1.1209 | 1.0838 | 1.0465 |
| 14.00 kg/cm²(g) | 1.1801 | 1.1246 | 1.0875 | 1.0503 |
| 17.50 kg/cm²(g) | 1.1825 | 1.1270 | 1.0899 | 1.0527 |
| 21.00 kg/cm²(g) | 1.1840 | 1.1285 | 1.0914 | 1.0542 |
Saturated steam properties
The enthalpy figures the conversion above is built on, at the pressures Indian boilers are specified at.
| kg/cm²(g) | bar(a) | T sat (°C) | h_f (kJ/kg) | h_fg (kJ/kg) | h_g (kJ/kg) | h_g (kcal/kg) | v_g (m³/kg) |
|---|---|---|---|---|---|---|---|
| 3.50 | 4.446 | 147.46 | 621.29 | 2121.55 | 2742.84 | 655.12 | 0.4187 |
| 7.00 | 7.878 | 169.78 | 718.23 | 2049.44 | 2767.67 | 661.05 | 0.2439 |
| 10.54 | 11.349 | 185.46 | 787.37 | 1994.43 | 2781.80 | 664.42 | 0.1722 |
| 14.00 | 14.743 | 197.48 | 841.03 | 1949.46 | 2790.49 | 666.50 | 0.1339 |
| 17.50 | 18.175 | 207.60 | 886.79 | 1909.43 | 2796.22 | 667.87 | 0.1093 |
| 21.00 | 21.607 | 216.33 | 926.71 | 1873.18 | 2799.89 | 668.74 | 0.0923 |
Common questions
Is 2256.9 kJ/kg the right datum constant?
It is the conventional trade figure, sometimes rounded to 2257 kJ/kg or quoted as 540 kcal/kg. Computed from IAPWS-IF97, the latent heat at exactly 100.00 °C is 2256.47 kJ/kg and at exactly one atmosphere it is 2256.54 kJ/kg. The spread against 2256.9 is under 0.02%, which is immaterial to any sizing decision — but it is worth stating once so nobody argues about it. These tools use 2256.9 kJ/kg throughout.
Why do two suppliers quote different capacities for the same duty?
Usually because they are quoting against different feedwater temperatures, or one is quoting F&A and the other actual evaporation at working conditions. Ask both to state the feedwater temperature and the working pressure their figure assumes. Without those two numbers, a capacity in kg/h is not comparable between quotations.
Is boiler horsepower the same thing?
It is the same idea in imperial units: one boiler horsepower is 34.5 lb/h evaporated from and at 212 °F, which is about 15.65 kg/h F&A 100 °C. You will meet it on imported datasheets. It is not Indian practice and is not a useful unit for specifying equipment here.
Can it convert boiler horsepower to kg/hr?
Yes. One boiler horsepower is 34.5 lb/h evaporated from and at 212 °F, which is the imperial statement of the same F&A datum this converter uses, so boiler horsepower to kg/hr is a direct conversion rather than an approximation.