How to Winterize a Sprinkler System

Last updated: September 14, 2026

Key Takeaways

• A straightforward residential setup usually takes about 30 to 90 minutes, depending on the number of zones and how easy the backflow device is to reach.
• That setup is how people overpressurize plastic pipe.
• If a contractor is winterizing your system, I would ask for a plain summary: how many zones were cleared, what pressure was used, and whether the backflow device was drained.
• It also applies to simple systems with only a manual drain or a blowout port.

Table of contents
– What winterizing actually does, and who should do it
– How do I winterize a sprinkler system step by step?
– How much does sprinkler winterization cost, and what changes the price?
– When should I stop and call a sprinkler contractor?
– What are the most common winterizing mistakes?
– What changes in cold climates, on slopes, or with special systems?
– How long should winterizing take, and what does a good job look like?

Before the first hard freeze, the lines need to be empty. Winterizing a sprinkler system means getting the water out of the pipes, valves, and backflow parts so expansion does not split anything. If you already have an in-ground irrigation system, a shutoff valve, and a way to clear the lines, this is a straightforward seasonal job; but if you have a backflow preventer you cannot isolate or you are not sure whether your system uses a blowout method, that is the point to call a sprinkler contractor. For many homeowners, the answer to how to winterize sprinkler system is shut off, drain, and verify each zone. Clean and boring. Good.

What winterizing actually does, and who should do it

Standing water is the enemy here. Winterizing removes it from the mainline, lateral lines, valve boxes, and backflow assembly enough to reduce freeze damage. It does not mean “turn the controller to off and hope for the best.” In a northern climate, even a small amount of trapped water can crack a PVC elbow, split a brass fitting, or break a plastic solenoid housing after one freeze cycle.

This applies to a standard residential in-ground sprinkler system with zone valves and a backflow preventer, usually a pressure vacuum breaker (PVB), reduced pressure zone assembly (RPZ), or double-check assembly. It also applies to simple systems with only a manual drain or a blowout port. I am assuming you already know where your controller is, where the irrigation shutoff valve is, and which parts of the system are above ground. If you do not know those things, you can still follow the steps below, but the risk of missing a low point goes up.

I would not treat this as a DIY job if you have an RPZ assembly and you do not know how it is configured, if the backflow device is in a location that can freeze, or if the system has a history of broken sprinkler heads and soggy valve boxes. The Irrigation Association’s winterization guidance is to use a qualified contractor when the backflow or blowout setup is unfamiliar. Those are the cases where a bad winterization costs more than the service call. For many homes, a seasonal blowout in the U.S. runs roughly in the low tens to low hundreds of dollars depending on zone count and access, and the price usually rises with more zones, multiple backflow devices, hard-to-reach valve boxes, or added drain work.

Short version? Shut off the water, drain what you can, and clear the remaining water from each zone with air if the system was designed for that. The hard part is knowing when “clear enough” is actually clear enough. That is where people get burned.

How do I winterize a sprinkler system step by step?

Shut off the supply first. Then drain the backflow and mainline, clear each zone, and leave the controller and valves in a safe state. Order matters because air should not be forced through closed or damaged parts until the water supply is isolated.

1. Shut off the irrigation water supply at the house-side shutoff or curb stop. Turn the valve fully closed and verify that no sprinkler head pops up when the controller starts a cycle for 10 to 15 seconds. If a head still sprays, the shutoff is not fully closed or there is another feed line.
2. Turn off power to the controller or set it to “off” and unplug the transformer if it has one. Confirm the display is blank or in a disabled state. If the controller still runs a program, it can open valves unexpectedly while the lines are being drained.
3. Open the test cocks or drain points on the backflow preventer, if the model has them. A PVB or RPZ often has small 1/4-turn test cocks; open them to relieve pressure and let water escape. Verify that water stops flowing after the line drains. If water keeps dribbling for several minutes, a shutoff valve may be leaking or the assembly may still be pressurized.
4. Drain low points, valve boxes, and any manual drain valves. Some systems have drain caps at low spots or in the basement near the mainline. Open them long enough for gravity to do its work, usually a few minutes per branch. If nothing comes out, do not assume the line is dry; a clogged drain, sag in the pipe, or trapped water in a hill section may be the reason.
5. Clear each irrigation zone with compressed air only if the system is rated for blowout and you can regulate pressure. Connect the air source to the proper blowout fitting, then work zone by zone. Keep the pressure conservative: for many residential PVC systems, about 50 psi is a common upper limit; fragile parts and polyethylene tubing often need less. Run each zone until the spray changes from mist to sputter and then to dry air. If you hear violent hammering, the pressure is too high or a valve is stuck open.
6. Cycle each zone separately and repeat until only dry air exits for several seconds. Use the controller or manual valve stem to open one zone at a time. Verify that every head on that zone pops up briefly and then stops spitting water. If one head stays low or one section still spits water after the rest is dry, that branch likely has a low pocket or a clogged head.
7. Leave the valves half-open and the backflow device drained. For many shutoff valves, a half-open position reduces seat damage from trapped pressure. Confirm the backflow test cocks are open and the assembly is not holding water. If you close everything tightly after blowout, residual water in a fitting can freeze and split the body.
8. Insulate exposed above-ground parts only after they are dry. Use insulated backflow covers or foam pipe insulation where appropriate, but do not wrap wet brass or plastic in a sealed way that traps water. Verify that insulation does not block the drain path or freeze-proof venting. Moisture trapped under a cover can also speed corrosion over the season.

A neat winterization is not the one blasting the most air. It is the one with no hidden pocket of water, no trapped pressure in the backflow assembly, and no controller waiting to wake the system back up in January.

How much does sprinkler winterization cost, and what changes the price?

Zone count, access, and whether the contractor only blows out the system or also drains and insulates exposed parts drive the cost. A simple one-zone or small-yard job is cheaper than a system with 8 to 12 zones, a basement shutoff, multiple valve manifolds, or a backflow device that needs extra handling. In many U.S. markets, a fall winterization visit is often priced in the low tens to low hundreds of dollars.

I would expect a basic fall winterization quote to include the blowout or drain-down, a visual check for obvious leaks, and a short run-through of the zones. What pushes the price up is not mystery labor; it is time. A contractor may need to locate buried valves, open a stuck test cock, clear water from a long mainline, or work around a backflow preventer mounted in a tight spot. If a company has to dig or repair damaged heads before winterizing, that becomes a repair job, not a standard seasonal service.

Ask what is included. One contractor may quote a low seasonal price but exclude the backflow assembly or charge extra per zone. Another may include a full controller reset, valve inspection, and a brief start-up note for spring. The lower number is not always the better value if it leaves water in a low spot.

A home in a mild frost area may only need drain-down and shutoff, while a place that regularly freezes hard needs a proper blowout schedule. That difference matters more than brand names or marketing language. A bad winterization often looks cheap in October and expensive in April, when a split manifold or cracked backflow body shows up as a leak the first time the system is pressurized again. The USDA hardiness map and local frost-depth guidance are better references than guesswork. Otherwise, you are rolling dice.

When should I stop and call a sprinkler contractor?

Stop when the system needs more than a simple shutoff-and-drain, because the wrong pressure or the wrong valve move can turn a maintenance job into a repair. These are the clearest stop points:

You have an RPZ assembly or another backflow preventer mounted where it can freeze: That device has internal check parts and relief valves that can be damaged by trapped water — call a contractor who knows how that assembly is drained and protected.
The system still holds pressure after the main shutoff is closed: A leaking shutoff, bad valve seat, or cross-connection may be feeding water into the lines — do not force air in until the supply path is understood.
You hear loud knocking or pipe hammer during blowout: Air pressure is too high, a zone is partially closed, or a valve is cycling erratically — stop and lower the pressure or hand the job off.
One or more zones never clear water after several cycles: A low spot, broken line, or clogged head may be trapping water — further blowing can scatter debris or stress fittings.
The controller, valves, or wiring are already acting up: A bad solenoid or stuck valve can open or close unpredictably — get the system repaired before winter, because a weak valve often fails under seasonal stress.

I would also stop if the air source is a shop compressor with no regulator and no gauge you trust. That setup is how people overpressurize plastic pipe. Many residential sprinkler systems are PVC or polyethylene, not rigid industrial piping. They do not appreciate 90 psi bursts. If you do not know the safe pressure for your system, that uncertainty alone is enough reason to hand it off. And if you have spray and drip on the same manifold, check the zone type before winterizing or consult a professional; the wrong pressure can damage the drip side.

What are the most common winterizing mistakes?

The usual mistakes are simple, and they get expensive fast because they damage parts you do not see until spring. Slow down. Verify each stage.

1. Shutting off the controller but not the water supply.
   Consequence: water stays in the lines and freezes.
   Better approach: close the irrigation supply first, then disable the controller.

2. Using too much air pressure.
   Consequence: split PVC fittings, blown seals, or damaged diaphragm valves.
   Better approach: use a regulated air supply and keep pressure conservative, often around 50 psi or less for many residential systems.

3. Blowing all zones at once.
   Consequence: uneven clearing and heavy strain on valves.
   Better approach: open one zone at a time and confirm dry air before moving on.

4. Ignoring the backflow preventer.
   Consequence: cracked brass, broken test cocks, or a spring assembly that leaks in spring.
   Better approach: drain and protect the backflow device according to its type and location.

5. Leaving the controller on an automatic schedule.
   Consequence: a surprise startup after partial winterization.
   Better approach: set it to off and remove power if needed.

6. Assuming one dry burst means the line is empty.
   Consequence: water remains in a low section or elbow.
   Better approach: repeat each zone until the spray is air only for several seconds, then check the obvious low points again.

A bad winterization has a familiar pattern: one cracked fitting, one wet valve box, or one dead zone that should have been protected. Usually, that means the job ended early — before the line was truly cleared.

What changes in cold climates, on slopes, or with special systems?

Gravity, soil, and pipe material change how water hangs around in the system, so the standard approach shifts too. A sloped yard can trap water in the downhill runs, and a system with long lateral lines may need longer blowout time than a compact suburban layout. Clay soil around valve boxes can hold moisture, which means the box itself needs to drain, not just the pipes inside it.

Polyethylene tubing is more forgiving than brittle, aged PVC in some layouts, but fittings and emitters still need clearing. Drip irrigation is its own case: drip lines and emitters often need lower pressure and more careful clearing because tiny emitters can be damaged by a hard blast. If your irrigation includes both spray zones and drip zones, do not treat them the same. Drip often needs a gentler, separately controlled winterization, and many contractors use a lower-pressure sequence for those lines.

Cold-weather practices also vary by region. In places where winter is mild and freezes are brief, some homeowners drain and shut down without a full blowout. In places with repeated hard freezes, that approach is weak. If the local ground freezes deeply, the system should be cleared more thoroughly, and above-ground backflow parts should be insulated or brought inside if the setup allows it. The National Weather Service notes that the first hard freeze date varies by region, which is why local timing matters.

The same goes for older systems. A 20-year-old manifold with brittle PVC elbows is less tolerant of aggressive air than a newer install. If parts are already cracked, winterization can reveal the damage rather than cause it, but the risk is still real. In that case, repair first, winterize second. No shortcuts.

How long should winterizing take, and what does a good job look like?

A straightforward residential system usually takes about 30 to 90 minutes, depending on the number of zones and how easy the backflow device is to reach. Bigger systems, buried valves, or stubborn drains take longer. The time is not the point; the verification is. A quick job that leaves water behind is not quick in the end.

A good winterization has a few visible signs. The controller is off. The irrigation supply is closed. The backflow assembly is drained and open where it should be open. Each zone spits water at first, then only dry air. No zone hammers. No valve box stays full of standing water. No exposed pipe is left under pressure. If you come back on a cold morning and the system still looks quiet, that is exactly what you want.

A bad job looks different. Heads may drip after the system is supposedly off. The backflow body may still hold water. The controller may still be live. One zone may clear while another never does. Or the contractor may leave without explaining which parts were drained and which were not. That last one matters because you need to know what was actually done before spring startup.

If a contractor is winterizing your system, I would ask for a plain summary: how many zones were cleared, what pressure was used, and whether the backflow device was drained. If the answer is unclear, that is not a small detail; it is a sign to ask again before the first freeze.