User Guide

Plumbing Design Assistance Manual l Appendix F – Pipe heat loss and surface temperature l 173
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
1½" Uponor PEX surface
temperature at 70°F/21.1°C ambient
Water
temp
(ºF)
Surface temperature (°F)
No insulation
½" insulation
1" insulation
1½" insulation
2" insulation
30 33.3 59.1 64.3 66.3 67.4
40 42.5 61.8 65.7 67.3 68.0
50 51.6 64.5 67.1 68.2 68.7
60 60.8 67.3 68.6 69.1 69.3
70 70.0 70.0 70.0 70.0 70.0
80 79.2 72.7 71.4 70.9 70.7
90 88.4 75.5 72.9 71.8 71.3
100 97.5 78.2 74.3 72.7 72.0
110 106.7 80.9 75.7 73.7 72.6
120 115.9 83.7 77.1 74.6 73.3
130 125.1 86.4 78.6 75.5 73.9
140 134.2 89.1 80.0 76.4 74.6
150 143.4 91.8 81.4 77.3 75.2
160 152.6 94.6 82.8 78.2 75.9
170 161.8 97.3 84.3 79.1 76.5
180 171.0 100.0 85.7 80.1 77.2
190 180.1 102.8 87.1 81.0 77.9
200 189.3 105.5 88.5 81.9 78.5
1½" Uponor PEX heat loss
at 70°F/21.1°C ambient
Water
temp
(ºF)
Heat loss (btu/hr·ft)
No insulation
½" insulation
1" insulation
1½" insulation
2" insulation
30 -15.6 -7.5 -5.4 -4.4 -3.9
40 -11.7 -5.6 -4.1 -3.3 -2.9
50 -7.8 -3.8 -2.7 -2.2 -1.9
60 -3.9 -1.9 -1.4 -1.1 -1.0
70 0.0 0.0 0.0 0.0 0.0
80 3.9 1.9 1.4 1.1 1.0
90 7.8 3.8 2.7 2.2 1.9
100 11.7 5.6 4.1 3.3 2.9
110 15.6 7.5 5.4 4.4 3.9
120 19.5 9.4 6.8 5.5 4.8
130 23.4 11.3 8.1 6.6 5.8
140 27.3 13.1 9.5 7.8 6.7
150 31.2 15.0 10.8 8.9 7.7
160 35.1 16.9 12.2 10.0 8.7
170 39.0 18.8 13.5 11.1 9.6
180 43.0 20.6 14.9 12.2 10.6
190 46.9 22.5 16.2 13.3 11.6
200 50.8 24.4 17.6 14.4 12.5