Cold Weather and Plumbing

Cold weather and plumbing; what should you expect from the plumbing system in your house or structure during the winter months? What exactly is happening and what can be done to counteract it? 

Cold weather and plumbing; Thermal Expansion

As the temperature drops seasonally certain changes occur in the plumbing systems that serve us, some subtle some marked. I will start by explaining some changes cold weather may make in your hot water supply.

The municipal water supply in my town, according to their web site, can range from 66 deg. F. down to 38 deg. F. Water like air expands when heated and shrinks when cooled.

If you have a tank style water heater in your home, any time you use hot water unheated water from the cold water supply side of your water system enters the water heater. When enough cold water enters to trigger the thermostat, the elements bring the new water up to the preset temperature. As the new water is being heated it is also expanding.We call this "thermal expansion"

Many water districts are now protecting their municipal water supply from lawn chemicals and other hazards by installing check-valves at the water meters that separate the water district’s pipes from the property owner’s pipe. These check-valves create a "closed system" downstream of wherever they are installed. Thermal expansion used to push water back into the supply system in the street, that is no longer possible if your meter has a check valve and you are now on a closed system.

There is always some degree of thermal expansion when the water heater is heating water. When the incoming temperature of the water is lower though and the target temperature of the thermostat is still the same, there will be more thermal expansion.

Combine this fact with the natural desire to take longer and hotter showers when it is cold outside. In the winter months thermal expansion can be a much greater issue. The last factor to consider is that water does not compress. 

The temperature and pressure relief valve is an emergency valve and is not designed to open frequently. It seals with an ordinary faucet washer. The washer may adhere to its seat, having never been opened, and be torn when the valve opens. It may also trap some piece of debris from within the tank and that debris may keep the valve washer from seating perfectly. The TPRV is not serviceable and I never want to open one unless I am removing it.

If you are on a closed water system and there are no drips or leaks in the system there is only one place for thermal expansion to go and that is out at the TPRV. The increasing force of the expanding water may open the TPRV and release water onto the floor or out through the outlet pipe of the TPRV. In most cases the TPRV simply closes till it must open again, but not always. If it fails to close you will have to turn the water off till the TPRV can be replaced.

The solution to the problem is to install a thermal expansion tank. You may not need a thermal expansion tank in the summer, but may not be able to do without one in the winter.

Cold weather and plumbing; Reduced water Heater Recovery Rate

If you use a fair amount of hot water, lets say half of the stored heated water in the tank, the tank will take a little time to heat that volume of incoming water to the preset target temperature. The amount of time a water heater takes to perform this task is called the recovery rate.

The recovery rate is affected by changes in the incoming water temperature because while the incoming temperature changes the target temperature remains the same. So as the temperature differential increases recovery rate diminishes.

The practical result is that just when you want to take that longer and hotter shower to warm up there is less hot shower water to be had, especially for the next person in line. Because the water heater is not recovering as quickly as it did in the warmer months.

Cold weather and plumbing in the ground

There are a few cold weather and plumbing issues for the buried water pipes that serve your home depending on what kind of pipe you have.

Galvanized water pipe forms iron oxide [rust] inside, but what you must remember is that the rust used to be the inside wall of the pipe so as the rust gets larger the pipe walls become thinner. Eventually the water will begin to seep out through the pipe wall at the thinnest points. This will usually soon stop because the holes that form clot themselves up with expanding rust around the weep hole. As you look along older indoor galvanized pipe systems you may see some of these built-up scabs of rust that if you scrap off will begin to weep. These pin holes will be at their leakiest when the weather changes and very cold water begins to flow through the old pipes. There will come a time usually in the late fall when these pin-holes may no longer close because the iron pipe and the iron oxide do not expand and contract at the same rate. The rust cannot adhere well enough to continue to plug the hole, the hole may at that point be too large to close again and there is a steady leak where in the summer there was only a scab of rust.

Many homes and businesses have building supply pipes in the ground outside that are made of PVC. PVC pipe becomes quite brittle when it gets cold. If there are any points along the supply that are under lateral stress caused by improper back-filling of trenches, or just natural ground settling and shifting, especially if there are bends or threaded adapters at those points fractures may develop in the pipe joints. Also, poorly glued PVC joints will tend to separate when the pipe material shrinks in the cold. Therefor late fall is the time when I get lots of calls about water pipe leaks in the ground.

Back to Frozen Water Pipes

Back to Water Heater Info