Jonathan Simon, Lubrizol Advanced Materials Inc.
Table of Contents
On a jobsite in mid-August, with temperatures climbing to 95°F in the shade, the risk of freezing weather on the home’s piping is likely not one of them, especially if they are working in a part of the country where freezing conditions are rare. Pipe freezing is a real concern.
But, common or not, freezing conditions do occur across the continental United States and pipes left unprotected can fail in those conditions and cause extensive damage.
In fact, homes in climates where freezing temperatures are infrequent often experience higher rates of failure than climates where freezing temperatures are more common because the practices that can protect pipes from freezing have been neglected.
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.
The Myth of the Freeze-Proof Pipe
It isn’t the pressure created by ice on the walls of the pipe that cause a pipe to burst. Instead, ice in the pipes forms a dam that blocks off water flow. As the ice expands, the water pressure builds behind the dam. When that pressure exceeds the burst pressure of the pipe, the pipe will fail. You can see how this happens in this video.
This means the two factors that determine the rate at which a pipe will freeze are its thermal conductivity and its burst pressure rating.
The thermal conductivity of the pipe 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.
A pipe’s quick burst pressure rating allows it to resist failure as water pressure builds behind the ice dam. Copper has the highest quick burst pressure rating at 3,000-4,000 psi, followed by CPVC at 1250 psi. PEX has the lowest quick burst pressure rating of the three materials at 475 psi.
Together the effect of thermal conductivity and burst pressure determines the rate at which different materials will fail when exposed to the same conditions. Copper, 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 freeze at about the same rate as copper, despite its lower burst pressure.
PEX, due largely to having the lowest burst pressure, will fail the fastest of the three. New PEX can expand or balloon somewhat to protect the pipe from bursting; however, this expansion can weaken the pipe wall, increasing the risk of future failure. In addition, as PEX ages, chlorine degradation may 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 “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.
Preventing Frozen Pipes
Once plumbers understand that even pipes in states like Texas and Florida require protection and there is no “freeze-proof” pipe, the question becomes how best to protect the water in pipes from freezing.
First, 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. Running pipe in conditioned spaces with the piping within the building insulation envelope is always preferred and may be required by code.
If pipes must be installed in unconditioned areas, use appropriate insulation to slow the rate of freezing. Heat trace systems may be used in connection with some piping materials to warm the pipe within these spaces. Be sure to use an insulation material or heat trace system that is compatible with the pipe. To determine compatibility with FlowGuard Gold CPVC, use the FBC™ System Compatible Program.
Another way to protect pipes is to install them under a slab foundation instead of overhead. 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.
Finally, be sure to seal any exterior wall penetrations as holes or gaps for cable or electrical penetrations can allow cold outside air to reach pipes, creating a “wind chill” effect that accelerates freezing within pipes. Sealing exterior penetrations and gaps can help prevent cold air from flowing around the pipes.
Preparing for the Unexpected
Cold weather in typically warmer climates is disruptive enough without home and building owners having to deal with frozen pipes and the damage they create. Plumbers can minimize or eliminate this risk by taking simple protective measures, For more plumbing best practices visit the Plumber Resources page on flowguardgold.com.
Jonathan Simon is the North American residential plumbing manager for Lubrizol Advanced Materials Inc., the parent company for FlowGuard Gold Pipe and Fittings.
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