Normally, this is not a problem because the main shut-off, zone valves and heads are below ground and stay relatively insulated. However, if the temperatures do dip down into the 20's, or temperatures remain below 32 degrees for an extended period of time, your irrigation system can be damaged.
A sprinkler system will freeze if the temperature falls below 32° F (0° Celsius). Now, most indoor sprinkler systems are inside of buildings or homes where the temperature won't ever drop into the danger zone.
At the freezing point of 32 degrees, Fahrenheit water left in your sprinkler system can expand and burst the pipes.
It takes a sustained hard freeze of around 28 degrees to potentially cause sprinkler damage.
You should shut off your irrigation system just before temperatures in your region begin to dip below freezing at night.
Pipes are most likely to burst when exposed to below-freezing conditions for six hours or more, which can happen throughout winter and early spring. Burst pipes could lead to a disaster, bringing severe water damage to your home.
It is best to turn on your system during the warmest time of the day when anticipating freezing conditions. Be sure the outside temperature is 40 degrees fahrenheit or above when you run your system. You ABSOLUTELY do not want to run your sprinkler system during a hard freeze as this will cause damage to your system.
Any of those circumstances could lead to pipes freezing – especially when the outside temperature is 20 degrees or colder. Generally, keeping your home at 55 degrees or warmer will prevent pipes from freezing.
If the temperature falls to 32 degrees or lower, your pipes are likely to freeze.
While you may be eager to get your lawn back to its pristine green state, it is important to remember that temperatures at and below 32 degrees Fahrenheit put your sprinkler system at risk of freezing.
So remember, during a hard freeze, turn off your sprinklers, not just because you might turn your lawn into a giant icicle but because you might also be responsible for street accidents.
Water freezes at 32 degrees, so technically that is the temperature at which it becomes possible for pipes to freeze as well. That said, it's not quite that simple. Pipes can freeze at 32 degrees or below, but it will take a sustained period of time for this to happen.
That's why fish survive under ice covering a pond by swimming in the warmer, denser water at the bottom of the pond. But the property of water that "is most fascinating is that you can cool it down well below 32 degrees Fahrenheit [zero Celsius] and it still remains a liquid," says Molinero.
The rule of the thumb is that it takes roughly 6-hours for water in your pipe to freeze after left in an unheated area. Meaning if you lose power at your home and the weather is reaching below freezing point, you have approximately 6-hours until the pipes will begin to freeze.
This is an option if your irrigation system is equipped with a manual drain valve. Simply turn off the water supply and open the manual valves at the ends and low points of the piping. Also, make sure to drain the backflow device.
If it is not going to rain before the freezing temperatures arrive, you should water plants thoroughly. This is because moist ground stays warmer than dry ground. Watering the night before the freeze arrives will insulate the root structure of the grass and plants, decreasing the potential for cold injury.
We all know that freezing begins at 32° F or 0° C, but at what point do pipes freeze within our own homes? Temperatures only need to drop to about 20° F for a few hours to put exposed pipes at risk.
Pipes that freeze most frequently are: Pipes that are exposed to severe cold, like outdoor hose bibs, swimming pool supply lines, and water sprinkler lines.
Another best practice to remember is that PVC piping lines should be installed at least one to two feet below ground to prevent damage from freezing and thawing cycles.
And those temperature swings and freezes can cause havoc with your outdoor irrigation system. Whether you face frozen pipes or some other form of winter pipe damage, you could end up with a flooded lawn and pricey landscaping problems and home exterior issues in the blink of an eye.
Nothing should be in that area between the bottom of the sprinkler heads and the imaginary horizontal plane parallel to the ceiling that is 18 inches below. This is done to allow an even and unobstructed spray pattern from the sprinklers when triggered to extinguish the fire.
The answer is “before temperatures generally dip below freezing at night.” The biggest problem that can strike an irrigation system in the winter is water leftover in the pipes and valves from the summer freezing.