Steam Load Calculator (lb/h)
Divide a heating load by the latent heat steam gives up as it condenses at your pressure, and you have the steam flow in pounds per hour.
Method reviewed October 26, 2026. Version 1.0.0. How it works
Result
- Steam required
- 1,058lb/h
- Latent heat at this pressure
- 945.6BTU/lb
1,058 lb/h of 15 psig steam (h_fg 945.6 BTU/lb).
- Uses latent heat only: the condensate is assumed to leave at the saturation temperature. Allow for piping heat loss and start-up warm-up loads separately.
- Saturation temperature
- 249.7°F
- Absolute pressure
- 29.7psia
- Condensate (as water)
- 2.12gpm
- Heat load
- 1,000,000BTU/h
Show the working
- Absolute pressure = gauge + atmospheric15 + 14.696 = 29.696 psia
- Saturated steam properties (IAPWS-95 via CoolProp, checked against NIST)T_sat = 249.7 °F, latent heat h_fg = 945.6 BTU/lb
- Steam = load ÷ latent heat1,000,000 ÷ 945.6 = 1,058 lb/h
Latent heat depends on pressure
When steam condenses it releases its latent heat of vaporization. That heat falls as pressure rises: about 970 BTU/lb at atmospheric pressure, about 946 BTU/lb at 15 psig and about 881 BTU/lb at 100 psig. So a load needs a few percent more pounds of steam at higher pressure.
The calculator uses saturated-water properties from the IAPWS-95 formulation (via CoolProp), checked against the NIST Chemistry WebBook to about 0.001 %.
What is and is not included
The calculation assumes dry saturated steam that condenses and leaves as condensate at the saturation temperature, so only latent heat is counted. Superheated steam, wet steam, subcooled condensate, piping heat loss and the warm-up load at start-up change the answer and should be added separately.
For heating water, the load is 500 × gpm × temperature rise.
Worked example
These are the example values the calculator opens with, and the result the engine calculates for them.
Inputs
- Load known as
- Heat load (BTU/h)
- Heat load
- 1,000,000 BTU/h
- Steam pressure (gauge)
- 15 psi
- Site elevation
- 0 ft
Result
- Steam required
- 1,058 lb/h
- Latent heat at this pressure
- 945.6 BTU/lb
- Saturation temperature
- 249.7 °F
- Absolute pressure
- 29.7 psia
- Condensate (as water)
- 2.12 gpm
- Heat load
- 1,000,000 BTU/h
1,058 lb/h of 15 psig steam (h_fg 945.6 BTU/lb).
Assumptions
- Steam is dry and saturated; it gives up only its latent heat and leaves as saturated condensate.
- Latent heat from IAPWS-95 (CoolProp), tabulated every 5 °F and interpolated in ln(pressure).
Limitations
- Superheated steam, wet steam and subcooled condensate change the heat per pound.
- Steam trap, piping and control sizing need the manufacturer’s data; steam systems must be serviced by qualified people.
Frequently asked questions
How much steam does 1,000,000 BTU/h need?
About 1,058 lb/h at 15 psig, or about 1,031 lb/h at 0 psig.
What is the steam temperature at 15 psig?
About 250 °F at sea level.
Does elevation matter?
Gauge pressure is measured from the local atmosphere, so the absolute pressure — and the steam properties — shift slightly at altitude.
Sources
- NIST Chemistry WebBook, SRD 69 — saturation properties of water — National Institute of Standards and Technology. Saturated water: e.g. 211.507 °F at 14.5663 psia with latent heat 971.037 Btu/lb, 301.252 °F at 68.2959 psia with 909.911 Btu/lb (thermochemical Btu).
- CoolProp — open-source thermophysical property library (version 8.0.0) — CoolProp developers (MIT licence). Equations of state for pure fluids and mixtures, incompressible fluids and brines, and IAPWS-IF97 water/steam; free for commercial use under its licence. Used here to generate the refrigerant saturation tables.
- Saturated steam table: generator and validation (packages/calc/reference/b7-g4/generate_g4_data.py) — FreeHVACCalculators.com. IAPWS-95 saturation pressure and latent heat (CoolProp 8.0.0) every 5 °F from 40 °F to 420 °F; agree with NIST WebBook to 0.002 %; saturation temperature interpolation error under 0.02 °F.
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