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Hot Water Heating Systems - Pressure Loss in Steel Pipes

Pressure loss nomogram for hot water steel pipes.

Pressure loss in hot water steel piping systems can be estimated from the nomogram below:

Hot water heating system - pressure loss piping diagram

The heat flow is based on temperature difference 20 oC.

  • 1 Pa = 10-6 N/mm2 = 10-5 bar = 0.1020 kp/m2 = 1.02×10-4 m H2O = 9.869×10-6 atm = 1.45×10-4 psi (lbf/in2)
  • 1 kW = 1,000 Watts = 3,412 Btu/h = 737.6/550 British hp = 1.341 British hp = 103/9.80665 kgf m/s = 737.6 ft
  • 1 liter/s = 10-3 m3/s = 3.6 m3/h = 0.03532 ft3/s = 2.1189 ft3/min (cfm) = 13.200 Imp.gal (UK)/min = 15.852 gal (US)/min = 792 Imp. gal (UK)/h
  • 1 m/s = 3.6 km/h = 196.85 ft/min = 2.237 mph
  • m (meter) = 3.2808 ft = 39.37 in = 1.0936 yd = 6.214×10-4 mile

Example - Pressure Loss in a Hot Water Heating Pipe

The pressure loss in a 2" BS 1387 hot water heating pipe with heat flow 100 kW can be estimated as indicated below

Hot water heating system - pressure loss diagram example

  • With temperature difference 20 oC the water flow is 1.2 liter/s
  • The flow velocity is 0.54 m/s
  • The pressure loss is 60 Pa/m
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