How to Winterize a Sprinkler/Irrigation System

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An in-ground irrigation system needs its own end-of-season shutdown, separate from the one you do for your outdoor faucets. The buried PVC and polyethylene laterals, the control valves, and the aboveground backflow assembly all hold water that has nowhere to drain on its own, and water that stays in a buried line through a hard freeze can crack a fitting, a valve body, or a sprinkler head you will not discover until you turn the system back on in spring. The job is three connected steps: shut off the water supply to the system, put the controller in off or rain mode, and clear the water out of the lines. The honest part most guides skip is that one of the three draining methods, the compressed-air blow-out, is the riskiest thing in this whole process and is often the part to hand to a pro. This guide walks the steps a homeowner can safely do and is clear about where the line falls.

Why In-Ground Irrigation Needs Its Own Winterizing

Your sprinkler system is a closed network of buried pipe that cannot drain by gravity the way a hose bib can. A single outdoor faucet has a short run of exposed pipe and an open spout, so opening it lets the water fall out. An irrigation system has a mainline, control valves, dozens of feet of lateral pipe, and pop-up heads, all sitting below grade with the water trapped inside. When that water freezes it expands, and the expansion is what cracks the pipe, splits a valve, or breaks a head.

Two things make irrigation a distinct job rather than a bigger version of spigot winterizing. First, the buried laterals hold a real volume of water that will not leave without either a drain point or forced air. Second, the system has an aboveground backflow preventer, a code-required assembly that protects your drinking water and that freezes easily because it sits out in the open air. Protecting that device is the step homeowners most often forget.

This post covers the in-ground system only. Winterizing outdoor faucets and hose bibs is a separate task, covered in our guide on winterizing outdoor faucets and hose bibs (160), and draining down a whole house you are leaving cold is covered in our guide on winterizing your home’s plumbing (128). What the backflow preventer is and why the law requires one is explained in our guide on the irrigation backflow preventer (164); here we only protect it from freezing.

Shutting Off the Supply and Putting the Controller in Off Mode

Start by closing the dedicated shutoff valve that feeds the irrigation system, then set the controller so it stops sending water. These two steps come before any draining, because you cannot clear a line that is still pressurized.

The supply shutoff for an irrigation system is usually a separate valve on the line that branches off to feed the sprinklers, often near the water meter, in a basement or utility area, or in a below-grade box. Close it. If you cannot find a dedicated irrigation shutoff and the system ties in close to your main, that uncertainty is itself a reason to have an irrigation professional handle the shutdown, because draining the wrong line or leaving the supply open defeats the whole job.

Next, deal with the controller, also called the timer. Rain Bird’s homeowner winterization guidance describes the simplest correct method for most systems: turn the timer to its OFF, RAIN, or RAIN/OFF setting and leave it plugged in. That stops the controller from signaling the valves to open, while keeping your watering program saved in memory so you do not have to reprogram everything in spring. Rain Bird also notes a practical reason to leave it powered: a plugged-in controller keeps a little heat inside the cabinet, which helps ward off condensation on the circuit board. Cutting power entirely works too, but on some models it erases the program. One real exception: if your system runs off a private well pump, the controller and pump need extra care so a stray signal does not run the pump dry, and that is a case to follow your equipment’s manual or call a pro.

The Manual and Auto-Drain Methods You Can Do Yourself

If your system was built with drain valves, you can clear most of the water yourself without any compressor. Which method you have depends on how the system was installed, so the first move is to find out whether you have manual drains, automatic drains, or neither.

The manual drain method uses valves placed at the low points of the piping. According to Rain Bird’s winterization guide, the procedure is to first close the mainline shutoff valve, then open one control valve to relieve the pressure sitting on the mainline, and only then slowly open each manual drain valve so the trapped water runs out at the low points. The order matters for a safety reason Rain Bird states plainly: the drain valve or cap is pressurized until you relieve that pressure, and opening it early can cause injury, so wear eye protection and relieve the pressure first. Open the valves slowly, not all at once.

The automatic drain method does most of the work on its own. These are spring-loaded valves installed on the lateral lines below the control valves, and Rain Bird explains that they open every time the system loses pressure, draining the laterals whenever the system shuts off. With auto-drains, shutting off the supply and depressurizing the system lets the valves release the water from the lateral pipes and heads. They do not, however, empty the control valves themselves, which can still hold standing water.

That is the honest limit of the do-it-yourself drains: gravity and drain valves clear the pipe runs, but water can stay trapped inside the control valves. Rain Bird is direct that draining the system does not remove water captured inside the valves, and that the diaphragm or actuator-style valves may need to be opened up and sponged out, or the bleed screw or solenoid left in the open position for winter. Leaving a valve in its manual-open position also prevents it from repressurizing over the winter. If your system has neither manual nor automatic drain valves, gravity draining is not an option, and the only way to clear the buried laterals is the compressed-air blow-out, which is the next section.

The Compressed-Air Blow-Out: How It Works and Why It’s Risky to DIY

The blow-out method pushes compressed air through the system to force the water out of the buried laterals and out the sprinkler heads, one zone at a time. It is the standard way to clear systems that have no drain valves, and it is also the step where homeowners do the most expensive damage. The core danger is simple: too much pressure, or air with too little volume behind it, cracks heads, fittings, and valves, and the flying debris and pressurized components can injure you.

Manufacturers set a maximum pressure, and it is low. Rain Bird states that air pressure must not exceed 50 pounds per square inch (psi) during the blow-out, and that a pressure-regulating valve must be used so the system cannot over-pressurize. Other makers set their own ceilings: Hunter Industries publishes a limit of 50 psi for polyethylene pipe and 80 psi for PVC pipe. Because the safe maximum depends on your equipment and pipe material, the rule is to follow your own system manufacturer’s stated maximum, not a number you read in a generic article. There is no single universal PSI.

The pressure limit is only half the problem. Rain Bird is explicit that air volume should be high and pressure low, and that you cannot substitute one for the other. Trying to use a small high-pressure, low-volume compressor, the kind that reads 120 psi on a little shop tank, is described by Rain Bird as a dangerous practice that places very severe stresses on the system. The reason is that air has much lower viscosity than water, so the same pressure that water can handle generates far higher stresses as air. Rain Bird notes that some small 2-horsepower shop compressors simply are not adequate for the job, and that the compressor needs to deliver real air volume, in the range of 10 to 25 cubic feet per minute, to move water without spiking the pressure.

Even done correctly, the blow-out has rules that protect the system. Rain Bird’s procedure says to keep at least one zone valve open the entire time the compressor runs, to start with the zone farthest from the air connection, and never to blow any single zone for more than two minutes at a time, because sustained heat from the compressed air can damage the pipe and the plastic gears inside the heads. You leave one zone open while shutting the compressor down, and you let the air bleed off before going near the components.

This is why the trustworthy move is usually “drain what you can, hire the blow-out.” Rain Bird itself notes that local irrigation contractors offer the service for a reasonable fee, often bundled with spring start-up, and suggests choosing a professional equipped to do it, especially on an extensive system. A pro has the right compressor, knows the pressure ceiling for your pipe, and stays out of the line of fire. If you do not own a compressor that can deliver high volume at low pressure, renting a small one and improvising is the wrong economy here, because a cracked manifold or a field of broken heads costs far more than a winterization call.

Protecting the Backflow Preventer and Aboveground Valves From Freezing

The aboveground backflow preventer is the part most likely to freeze and the part most often skipped, because it sits exposed to the air with water inside it. Protecting it is a real step, not an optional one.

Start by draining the assembly. Rain Bird’s guidance is to leave the shutoff valves on the backflow device open after draining it, and to leave any ball-type test cocks and shutoff valves at roughly a 45-degree angle, halfway open, so water cannot sit against the internal seals and freeze them. Many residential backflow assemblies have small test cocks you can open to let the water out; opening them releases the water trapped in the body. Once the assembly is drained and the valves are set partway open, insulate it. Rain Bird suggests insulating the device or using heat tape under extreme conditions, and an insulated bag or wrap rated for backflow assemblies is the common homeowner approach. One caution from Rain Bird’s controller guidance applies to the device too: do not block the air vents and drain outlets when you wrap it, because the assembly needs those openings to vent.

Two boundaries are worth stating clearly. First, the winter protection here is just that, protection from freezing. The backflow preventer is a code-regulated device that protects your drinking water from contamination, and its installation, repair, and required annual testing are not DIY tasks; for what the device does and why your jurisdiction requires it, see our guide on the irrigation backflow preventer (164). Second, manufacturers differ on the exact winterizing steps for a given assembly, so Rain Bird’s own advice is to check with the device manufacturer for the specific technique. If you are unsure whether your backflow assembly is fully drained, that is a reasonable thing to leave to the same pro who handles the blow-out.

Frequently Asked Questions

Can I winterize my sprinkler system without an air compressor?
Sometimes, but only if your system was built with drain valves. If you have manual drain valves at the low points, you can close the supply, relieve the pressure through a control valve, and open the drains to let the water out. If you have automatic drain valves, they release the water from the laterals on their own once the system loses pressure. If your system has neither, gravity cannot clear the buried laterals, and the only way to remove that water is the compressed-air blow-out, which usually means hiring an irrigation professional. Either way, you still need to drain and protect the aboveground backflow assembly.

Is blowing out sprinklers myself safe?
It carries real risk, which is why manufacturers and most guides treat it carefully. The danger is over-pressurizing the system: too much pressure, or a small high-pressure low-volume compressor, can crack heads, fittings, and valves and throw debris, and the maximum safe pressure is low, with Rain Bird capping it at 50 psi and requiring a pressure regulator. The job also needs a compressor that delivers high air volume rather than high pressure, a limit of no more than two minutes per zone, and keeping clear of the components. Many homeowners do not own a suitable compressor, so the common and safer choice is to do the gravity drains yourself and hire the blow-out from an irrigation contractor.

This article is general information, not professional advice. For the compressed-air blow-out, any work on the backflow assembly beyond draining and insulating it, a well-pump system, or a system you are unsure how to drain, consult a licensed plumber or a qualified irrigation professional.

Sources

Rain Bird, Homeowner’s Guide to Winterization: https://www.rainbird.com/media/1332
Rain Bird, How Do I Winterize My Irrigation System?: https://www.rainbird.com/homeowners/how-do-i-winterize-my-irrigation-system
Hunter Industries, Winterizing Your Irrigation System: https://www.hunterirrigation.com/winterizing-your-irrigation-system

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