Heat loss from 1/2" to 12" steel pipes at various temperature differences between pipe and surrounding air are indicated in the diagram and table below:
| Heat loss from Fluid inside Pipe (W/m) | |||||||||||||
| Nominal bore | Temperature Difference (oC) | ||||||||||||
| (mm) | (inch) | 50 | 60 | 75 | 100 | 110 | 125 | 140 | 150 | 165 | 195 | 225 | 280 |
| 15 | 1/2 | 30 | 40 | 60 | 90 | 130 | 155 | 180 | 205 | 235 | 280 | 375 | 575 |
| 20 | 3/4 | 35 | 50 | 70 | 110 | 160 | 190 | 220 | 255 | 290 | 370 | 465 | 660 |
| 25 | 1 | 40 | 60 | 90 | 130 | 200 | 235 | 275 | 305 | 355 | 455 | 565 | 815 |
| 32 | 1 1/4 | 50 | 70 | 110 | 160 | 240 | 290 | 330 | 375 | 435 | 555 | 700 | 1000 |
| 40 | 1 1/2 | 55 | 80 | 120 | 180 | 270 | 320 | 375 | 420 | 485 | 625 | 790 | 1120 |
| 50 | 2 | 65 | 95 | 150 | 220 | 330 | 395 | 465 | 520 | 600 | 770 | 975 | 1390 |
| 65 | 2 1/2 | 80 | 120 | 170 | 260 | 390 | 465 | 540 | 615 | 715 | 910 | 1150 | 1650 |
| 80 | 3 | 100 | 140 | 210 | 300 | 470 | 560 | 650 | 740 | 860 | 1090 | 1380 | 1980 |
| 100 | 4 | 120 | 170 | 260 | 380 | 585 | 700 | 820 | 925 | 1065 | 1370 | 1740 | 2520 |
| 150 | 6 | 170 | 250 | 370 | 540 | 815 | 970 | 1130 | 1290 | 1470 | 1910 | 2430 | 3500 |
| 200 | 8 | 220 | 320 | 470 | 690 | 1040 | 1240 | 1440 | 1650 | 1900 | 2440 | 3100 | 4430 |
| 250 | 10 | 270 | 390 | 570 | 835 | 1250 | 1510 | 1750 | 1995 | 2300 | 2980 | 3780 | 5600 |
| 300 | 12 | 315 | 460 | 670 | 980 | 1470 | 1760 | 2060 | 2340 | 2690 | 3370 | 4430 | 6450 |
The heat loss value must be corrected by the correction factor for certain applications:
| Application | Correction factor |
| Single pipe freely exposed | 1.1 |
| More than one pipe freely exposed | 1.0 |
| More than one pipe along the ceiling | 0.65 |
| Single pipe along skirting or riser | 1.0 |
| More than one pipe along skirting or riser | 0.90 |
| Single pipe along ceiling | 0.75 |
