User Guide

Plumbing Design Assistance Manual l Appendix F – Pipe heat loss and surface temperature l 167
1. All calculations based on cylindrical thermal resistance methodology (ASHRAE).
2. Based on uid velocity of 8 ft./sec. at 160°F/71.1°C (maximizing heat transfer from 100% water).
3. Pipe convection set to be 1.761 Btu/hr•ft²•°F (based on standard value for free convection of air).
4. This heat loss comparison uses 0.24 Btu•in/(hr•ft2•°F) as the insulation thermal conductivity.
This is a standard value for berglass pipe insulation at a 100°F/37.8°C mean temperature.
Pipe heat loss and surface temperature
2½" Uponor PEX surface
temperature at 50°F/10°C ambient
Water
temp
(ºF)
Surface temperature (°F)
No insulation
½" insulation
1" insulation
1½" insulation
2" insulation
30 32.5 44.3 46.9 48.0 48.5
40 41.3 47.2 48.5 49.0 49.3
50 50.0 50.0 50.0 50.0 50.0
60 58.7 52.8 51.5 51.0 50.7
70 67.5 55.7 53.1 52.0 51.5
80 76.2 58.5 54.6 53.0 52.2
90 85.0 61.3 56.2 54.0 52.9
100 93.7 64.1 57.7 55.1 53.7
110 102.4 67.0 59.2 56.1 54.4
120 111.2 69.8 60.8 57.1 55.1
130 119.9 72.6 62.3 58.1 55.9
140 128.7 75.4 63.9 59.1 56.6
150 137.4 78.3 65.4 60.1 57.3
160 146.1 81.1 66.9 61.1 58.1
170 154.9 83.9 68.5 62.1 58.8
180 163.6 86.7 70.0 63.2 59.5
190 172.3 89.6 71.6 64.2 60.3
200 181.1 92.4 73.1 65.2 61.0
2½" Uponor PEX heat loss
at 50°F/10°C Ambient
Water
temp
(ºF)
Heat loss (btu/hr·ft)
No insulation
½" insulation
1" insulation
1½" insulation
2" insulation
30 -12.0 -5.4 -3.7 -3.0 -2.5
40 -6.0 -2.7 -1.9 -1.5 -1.3
50 0.0 0.0 0.0 0.0 0.0
60 6.0 2.7 1.9 1.5 1.3
70 12.0 5.4 3.7 3.0 2.5
80 18.0 8.0 5.6 4.5 3.8
90 24.0 10.7 7.5 6.0 5.1
100 30.0 13.4 9.3 7.5 6.4
110 36.0 16.1 11.2 8.9 7.6
120 42.0 18.8 13.1 10.4 8.9
130 48.0 21.5 14.9 11.9 10.2
140 54.1 24.1 16.8 13.4 11.5
150 60.1 26.8 18.6 14.9 12.7
160 66.1 29.5 20.5 16.4 14.0
170 72.1 32.2 22.4 17.9 15.3
180 78.1 34.9 24.2 19.4 16.5
190 84.1 37.5 26.1 20.9 17.8
200 90.1 40.2 28.0 22.4 19.1