Frozen pipes aren’t only a problem in certain climates or areas of the country. According to the National Oceanic and Atmospheric Administration, the vast majority of the United States can expect the temperature to drop below freezing at least once a decade.
When freezing weather strikes, homes in the southern states and warmer climates can actually be more vulnerable to failure than those in colder, northern climates. This is because both building codes and installer practices in the northern states assume freezing temperatures and take precautions, while local codes in warmer climates are not as strict, increasing the risk of frozen pipes.
That’s why no matter where you are working — or what piping material you are working with — it’s important to understand how pipes freeze and the steps you can take to minimize the risk of failure from freezing.
How pipes fail when exposed to freezing temperatures
Many people assume it is the pressure of ice on the wall of the pipe that causes a failure, but that’s not the case. Instead, as this video shows, frozen pipes burst because ice in the pipe forms a dam that blocks the flow of water.
As the ice expands, the water pressure builds behind the dam and the failure occurs when that pressure exceeds the burst pressure of the pipe material.
Once you know the real reason pipes fail from freezing, you understand the factors that influence the freezing rate for a particular material.
The first is the thermal conductivity of the pipe material, which determines how well the material can resist cooling. Of the three commonly used residential plumbing materials, CPVC resists cooling the best, followed by PEX. Copper has the highest thermal conductivity, meaning it has the least resistance to cooling.
Equally important is the material’s burst pressure rating, which allows it to resist failure as water pressure builds behind the ice dam. Copper has a quick burst pressure of 3,000-4,000 psi. CPVC has a quick burst pressure of 1,250 psi. And PEX has a quick burst pressure of 475 psi.
By combining the effect of thermal conductivity and burst pressure, you can calculate the rate at which different materials will fail when exposed to the same conditions. Copper, for example, with its high thermal conductivity, provides little resistance against cold air reaching the water in the pipe, but its high burst pressure allows it to withstand the rising water pressure longer than other materials.
CPVC’s low thermal conductivity provides more protection for the water in the pipe and so will burst at about the same rate as copper, despite its lower burst pressure.
PEX, due largely to having the lowest burst pressure, would be expected to fail the fastest of the three. New PEX can expand or balloon somewhat to protect the pipe from bursting, but this expansion can weaken the pipe wall, increasing the risk of future failure. In addition, as PEX ages, chlorine degradation can reduce the elasticity of the inner pipe wall, diminishing any advantages the elasticity of the material provides in terms of freeze-break resistance.
The thing to remember is that all pipes will fail when exposed to freezing conditions for long enough — there is no such thing as a freeze-proof pipe — so you should take steps at installation to protect pipes, regardless of what material you are working with or what part of the country you are working in.
Five best practices for avoiding frozen pipes
Here’s how to protect pipes against freezing.
1. Always plan for cold weather.
It’s essential not to assume that the pipes you’re installing will be immune to extreme weather over their lifetime. With weather patterns becoming increasingly unpredictable, planning for the worst has never been more critical.
2. Avoid installing pipes in unconditioned areas.
Attics, crawlspaces, overhangs, exterior walls and other unconditioned spaces are the first to get cold when outside temperatures drop and therefore present the biggest risk for frozen pipes. Running pipe in conditioned spaces with the piping within the building insulation envelope is always preferred and may be required by code.
3. Use appropriate insulation practices.
When installing pipes in unconditioned areas, it is essential to use compatible insulation to reduce the risk of freezing. In some cases, heat trace systems can be used with certain piping materials to keep the pipe warm in these spaces. Ensure that both the insulation material and any heat trace system are compatible with the specific type of pipe being used. For example, to determine compatibility with FlowGuard Gold CPVC, use the FBC System Compatible Program.
4. Install pipes under slab foundations instead of overhead.
By installing piping beneath the slab, the natural geothermal insulation of the ground will often be adequate to protect against frozen pipes. In addition, running pipes under the slab can have other benefits to builders and contractors, including faster installations and lower installed costs. Always verify that local codes allow installation of water distribution piping under slab.
5. Seal exterior wall penetrations.
Openings or gaps in exterior walls for cables or electrical penetrations can let cold air infiltrate and surround pipes, creating a windchill effect that speeds up freezing. Properly sealing these gaps and penetrations helps block cold air from reaching the pipes and reduces the risk of freezing.
To access more plumbing resources, visit FlowGuardGold.com.
Jonathan Simon is the North American residential plumbing manager for The Lubrizol Corporation.
