What temperature does indoor plumbing freeze?

Answer 1

Assuming you don't mean water heating systems, and just mean normal fresh (drinking) water systems, then they freeze at 0 degrees Centigrade like all water.

But in the case of for example a home, the Plumbing protected from freezing in a few different ways.

Firstly most homes that are lived in have some form of heating, so this keeps the ambient temperature of the water in the pipes above freezing.

Pipes that are in places more likely to be exposed to freezing, such as lofts, and roof cavities will be insulated with pipe lagging to protect them from freezing. Plus remember those pipes in roof cavities will benefit from heat rising from the home/building, helping to keep those pipes above freezing.

If the subject of your question is in relation to 'burst' pipes caused by frozen water in the pipes expanding and literally tearing the pipes apart, then this will start to happen at about 20 Degrees Fahrenheit or -6 degrees Centigrade.

Remember that a little freezing is not a major problem, as plumbers sometimes use special freezing kits, that will freeze a short section of pipe to block it off temporarily, while they work on the pipes.