The pipes bursting below 55° rule of thumb is because cold water is at ground temperature (aka very cold in the winter) and the pipes tend to be at the edges of living spaces so will be much cooler than the living space. Additionally, it doesn’t need to fully freeze to burst, just enough to create a blockage temporarily.
Basically, you never know what bizarre choices were made in the utility layout of the home someone lives in so giving a rule of thumb that has a comfortable safety margin is the safest bet
The pipes bursting below 55° rule of thumb is because cold water is at ground temperature (aka very cold in the winter) and the pipes tend to be at the edges of living spaces so will be much cooler than the living space. Additionally, it doesn’t need to fully freeze to burst, just enough to create a blockage temporarily.
Basically, you never know what bizarre choices were made in the utility layout of the home someone lives in so giving a rule of thumb that has a comfortable safety margin is the safest bet