Water trapped inside an irrigation system during freezing temperatures can cause catastrophic damage. When water transitions to ice, it expands its volume by approximately 9%, creating immense pressure within the pipes. This pressure, which can exceed 600 pounds per square inch, is far greater than what most residential plumbing materials, like PVC or polyethylene pipes, are designed to withstand. This stress causes components such as underground pipes, backflow preventers, and sprinkler heads to crack or burst. The only reliable method to prevent this damage is winterization, which involves removing all water from the system before a hard freeze occurs.
Determining the Right Time to Act
The timing for winterizing a sprinkler system is a function of both temperature and regional climate, but it must happen well before the first sustained freeze. Experts advise completing the process when the forecast consistently predicts temperatures to drop below 32°F for several consecutive hours, particularly overnight. This threshold is important because a light, brief frost may not penetrate the ground deep enough to affect buried pipes, but a prolonged cold snap will.
Homeowners in northern climates, where the frost line is deep, must prioritize early winterization, in early to mid-fall. Conversely, those in transitional zones with milder winters may only need to act when a severe, unexpected cold front is imminent. Waiting until the ground has already frozen is too late, as the process of removing water from a partially frozen system can be more challenging. Monitoring long-range forecasts is the most reliable way to ensure the system is completely dry before the cold arrives.
Comprehensive Winterization Steps
The first step in preparing an irrigation system for winter is to shut off the main water supply. This primary valve is often located near the water meter, in a basement, or within an exterior valve box. Once the main supply is secured, the next action involves relieving pressure and draining the above-ground components.
Any water remaining in the backflow preventer must be drained immediately. Opening the test cocks and shut-off valves on this device allows standing water to escape, significantly reducing the risk of a freeze-induced crack. For systems equipped with manual drain valves at low points, these should also be opened to release any standing water trapped by gravity.
The most thorough method for clearing the remaining water from the underground pipes is the compressed air blowout, a step that often requires professional equipment and expertise. A large-capacity air compressor is connected to a dedicated port on the system, and regulated air is systematically pushed through the pipes, zone by zone. This process is highly effective but requires strict adherence to safety guidelines.
The air pressure should be carefully regulated, maintained between 40 and 60 pounds per square inch (PSI) for most residential systems using plastic piping. Exceeding 80 PSI can rupture pipes, seals, or sprinkler heads, turning a preventative measure into a repair job. Compressed air should never be blown into a zone for too long, as the friction can generate heat that damages internal components. Anyone near the system must wear eye protection due to the risk of flying debris.
Addressing Unwinterized Systems During a Freeze
If an unexpected freeze occurs before winterization is complete, immediate action is necessary to mitigate potential damage. The first step is to locate and shut off the main water supply to the irrigation system to prevent a leak if a pipe has burst. Turning off the water supply limits the amount of water damage that can occur when the ice plug thaws and pressurized water floods the area.
Homeowners should inspect any above-ground components, particularly the backflow preventer and sprinkler risers, for visible signs of damage, such as cracks or splits. These parts are the most susceptible to the initial freeze and often fail first. If any damage is noted, it confirms that a repair will be necessary once the weather warms.
Resist the temptation to thaw frozen pipes using high-heat methods like open flames or boiling water. Applying direct or intense heat can cause a rapid temperature change, leading to thermal expansion that may crack the pipe or component instantly. The safest approach is to wait for the natural thaw, which allows the ice to melt gradually.
Damage from a freeze is often not apparent until the ice melts, allowing leaks to begin. Once temperatures rise above freezing, the system should remain shut off until a professional can inspect all lines and components for integrity. Attempting to repressurize a system after a freeze without a professional inspection risks turning a minor crack into a major flood.