Temperature Drop Calculator For Hydronic Piping

Calculates the Temperature Change of Water Flowing in a Pipe (Reference: 2009 ASHRAE HoF, Chapter 4, Equation 48, (pg 4.21))

This calculator estimates the temperature drop (or rise) of water flowing in a pipe.


(Input information may generally be be obtained from design documents or field measurements)

  • Line 1. Enter the temperature of the water entering the pipe
  • Line 2. Enter the ambient temperature (temperature of the air surrounding the pipe)
  • Line 3. Enter the wind speed of the ambient air in miles per hour
  • Line 4. Enter the flow rate of the water carried by the pipe in gallons per minute.
    Note: Calculator does not screen for reasonable flow velocities, Hydronic piping is normally sized for flow velocities between 5 and 12 feet/sec
  • Line 5. Enter the length of the piping run in feet
  • Line 6. Select the nominal pipe size in inches
  • Line 7. Select the nominal thickness of insulation in inches
  • Line 8. Select an insulation material.
    Note: Calculator does not screen for material temperature limitations.
  • Line 9. Select thermal emittance of the outer jacket material.

Note: NA = Insulation Size Not Available. Some sizes and thicknesses may not be commercially available.


  • One dimensional, steady state heat transfer
  • U-factor constant at average conditions
  • Thermal resistance of film at inner pipe surface neglected
  • Thermal conductivity based on ASTM Specification Values. Refer to the introductory notes for further clarifications.
Input Information
1. Entering water temperature, °F
2. Ambient air temperature, °F
3. Wind speed, mph
4. Flow rate of water, gpm
5. Length of piping run, ft
6. Select pipe size, NPS
7. Select thickness of insulation, in.
8. Select insulation material
9. Select emittance of jacket material