Steam Loss

ESTIMATING THE COST OF STEAM LOSS
THROUGH THE ORIFICE OF A STEAM TRAP
By Henry Manczyk, CPE, CEM
Manczyk Energy Consulting
Investigation of steam loss in a steam system, or routine or preventive maintenance procedures, may reveal
that one or more steam traps are leaking. How does the cost of repairing or replacing the defective steam
traps compare to the value of the lost steam?
When a steam trap malfunctions, steam in form of vapor escapes through the outlet valve or orifice. The
steam that escapes is wasted energy that cannot be recovered. By determining the amount of steam that
escapes, it is possible to determine the financial loss and whether or not a trap maintenance and repair
program would be beneficial. Steam loss through an orifice can be estimated using a variant of the Napier
formula:
Steam Flow (lb/hr) = 24.24 x Pa x D²
Pa = Pgage + Patmospheric
Pa = Absolute Pressure, psia
Pgage = Gage Pressure, psig
Patmospheric = Atmospheric Pressure, psi = 14.696 psi
D = Diameter of Orifice, in.

where:

Example

Pgage =
Pa =
D=

5
19.696
0.1875

psig
psia
in

W = 24.24 x 19.696 psia x (.1875 x .1875) = 16.78 lbs/hr

ESTIMATING ANNUAL FUEL COST PER STEAM TRAP
For a trap that is leaking continuously throughout the entire heating season, the cost for the loss of steam in
the trap can be determined using the following formulas:
Formula for Annual Fuel Cost per Trap - Using Cost per MMBtu
in Natural Gas in Commercial Heating Systems:
Q = L x H x E x 10-6 x C
BE
Energy Lost ($)
Lb/Hr of steam lost = 16.78 lbs/hr (0.187” orifice, 5 psig)
Hours in heating season = 5,808
Latent heat of steam at 5 psig = 960.8 Btu/lb
MMBtu/Btu
Cost of gas per million Btu = $6.23
Boiler Efficiency = 80%

where:

Q=
L=
H=
E=
10-6 =
C=
BE =

Q

(16.78) (5,808) (960.8) (10-6) (6.23)/0.80 = $729.20

=

Equipment Cost
If a steam trap maintenance program were to be implemented and the cost to repair or replace each
defective...