per Fahrenheit degree
Thermal expansion coefficientexact by definition
The reciprocal Fahrenheit degree is the customary US expansion coefficient. Because a Fahrenheit degree is five-ninths of a kelvin, a coefficient of one per Fahrenheit degree is 1.8 per kelvin, and that factor of 9/5 is exact by definition. Copper is 9.2e-6 per Fahrenheit degree, steel 6.5e-6, and PVC about 30e-6.
Watch out: The direction of the 1.8 is easy to get backwards. Per Fahrenheit degree gives a SMALLER number than per kelvin for the same material, because a Fahrenheit degree is a smaller temperature step and produces less expansion. Going from per-°F to per-K, multiply by 1.8.
| 1 1/°F | 1.8 1/K |
Pipe expansion is the everyday use. A 100 foot copper run heated 100 F° grows by 9.2e-6 × 1200 in × 100 = 1.1 inches, which is why hydronic mains get expansion loops and why a rigidly anchored riser will eventually tear something out of a wall.