How to Winterize a Sprinkler System (Blowout Method)

Why Winterizing Your Sprinkler System Matters

Water expands when it freezes — by about 9 percent — and that expansion is strong enough to crack sprinkler pipes, split valves, shatter backflow preventers, and pop sprinkler heads right out of the ground. A system that is not winterized before the first hard freeze can suffer hundreds of dollars in damage, most of it hidden underground until spring startup reveals geysers where your lawn used to be.

Winterizing means getting the water out of the system before freezing temperatures arrive. There are three common methods: manual drain valves, automatic drain valves, and the compressed-air blowout. This guide focuses on the blowout method, which is the most thorough and the standard approach in regions with deep freezes — but it involves compressed air, which demands serious respect for safety.

When to Winterize

Winterize before the first hard freeze (temperatures below about 28°F / -2°C for several hours), not after. A light frost will not damage a charged system, but a hard freeze can. Practical timing:

• Check your area’s average first-frost date and plan to winterize 2–3 weeks before it.
• Watch the forecast: if a hard freeze is predicted and you have not winterized yet, do it immediately — or at minimum shut off the water to the system and drain the backflow preventer.
• In mild climates where the ground never freezes deeply, winterizing may be optional — but draining the backflow preventer and exposed components is still wise.

The Three Winterizing Methods

• Blowout (compressed air): forces water out of every line, head, and valve with compressed air. Most thorough; required in cold climates. This guide’s method.
• Manual drain: systems with drain valves at low points can be drained by opening the valves. Simpler, but residual water can remain in dips and heads.
• Automatic drain: auto-drain valves at low points open when pressure drops. Convenient, but valves can clog or fail — many pros still recommend a blowout in truly cold regions.

If your system has drain valves and you live where freezes are brief and shallow, the manual method may suffice. For full protection in freezing climates, do the blowout.

Safety Warnings: Compressed Air Is Dangerous

Read this section completely before you begin. Skipping safety steps with compressed air can cause serious injury.

• Wear eye protection — mandatory. Blowout sends water, dirt, and debris blasting out of sprinkler heads at high velocity. Safety glasses or goggles are non-negotiable for everyone in the area.
• Never exceed the pressure limits: maximum 50 PSI for polyethylene (poly) pipe and 80 PSI for PVC pipe. Exceeding these can rupture pipes or blow fittings apart. Set the compressor regulator before connecting, and verify with a gauge.
• Never stand over or look directly into sprinkler heads during blowout. Heads can pop up violently or eject debris.
• Keep children and pets away from the work area during the entire procedure.
• Blow out zone by zone — never pressurize the entire system at once. Open one zone valve at a time so air has a clear exit path; a closed system with nowhere to go builds dangerous pressure.
• Do not run the compressor into a closed system. Always confirm a zone is open and flowing before the compressor builds pressure against it.
• Let the compressor cool between zones if it is working hard; overheated compressors can fail.
• If you are unsure about your pipe type, your system’s layout, or any step — hire a professional. A pro blowout typically costs far less than repairing burst pipes, and there is no shame in it. This is genuinely the one DIY task in this guide where calling a pro is a completely respectable first choice.

What You’ll Need

• Air compressor: a model that can sustain adequate airflow matters more than tank size — look for at least 4–5 CFM at 40–50 PSI for residential systems. Small pancake compressors often cannot keep up; you may need to rent a larger towable or wheeled unit.
• Blowout adapter fitting: connects the compressor hose to your system — commonly a quick-connect to garden-hose thread, or a fitting for the backflow preventer test cocks. Buy the right adapter for your connection point before you start.
• Adjustable pressure regulator with gauge (if not built into the compressor).
• Safety glasses or goggles.
• Valve key or screwdriver for manual zone valves (if your controller cannot open zones manually).
• Towels and insulation for the backflow preventer after blowout.

Step-by-Step: The Blowout Method

Step 1: Shut off the water to the sprinkler system

Close the main shutoff valve for the irrigation system (usually in the basement, crawl space, or a valve box near the water meter). If you are not sure which valve feeds the sprinklers, see our guide on finding your water shutoff valves. Leave the system controller in the Off or Rain position for now.

Step 2: Relieve pressure and drain the backflow preventer

Open a manual drain valve or a hose bib on the system side to relieve pressure. If you have a backflow preventer (required in most areas), open its test cocks with a screwdriver to let water drain out — these brass devices are among the most freeze-vulnerable and expensive components.

Step 3: Set up the compressor

Position the compressor near your connection point. Set the regulator to the correct maximum for your pipe — 50 PSI for poly, 80 PSI for PVC — before connecting anything. Double-check the gauge. Connect the compressor hose to the system via your blowout adapter (common connection points: the backflow preventer test cock, a dedicated blowout port, or a hose bib downstream of the shutoff).

Step 4: Open the first zone

Put on your eye protection. Using the controller’s manual mode (or a valve key), open only zone 1. Confirm the zone valve is open before introducing air.

Step 5: Introduce air gradually

Start the compressor and open the air valve slowly. Water will sputter from the heads, then turn to mist, then to mostly air. Let each zone blow for about 2 minutes after only air (no water mist) is coming out — but do not run air through a zone longer than necessary, as the friction heat from compressed air can damage components over extended runs.

Step 6: Move through the remaining zones

Close zone 1, open zone 2, and repeat. Work through every zone one at a time. Never have two zones pressurized simultaneously with a small compressor — and never leave the compressor running against a closed system.

Step 7: Do a second pass

Water settles into low spots between blows. Run through all zones a second time, briefly (30–60 seconds each), to clear what resettled. Two short passes beat one long one.

Step 8: Shut down and disconnect

Turn off the compressor, close all zone valves, disconnect the hose and adapter, and close the test cocks on the backflow preventer (leave them at a 45-degree angle on some models per manufacturer guidance — check yours).

After the Blowout: Protect the Above-Ground Components

• Insulate the backflow preventer with a purpose-made insulated pouch or wrap it in towels inside a plastic bag. It sits above ground and is the most freeze-exposed part of the system.
• Leave the controller powered (it keeps its programming and clock), but set it to Off or Rain mode so it does not try to run zones over winter.
• Shut off and drain any hose bibs on the irrigation line, and see our outdoor faucet winterizing guide for the house spigots.
• Note any heads that behaved oddly during blowout (weak pop-up, tilted spray) — flag them for spring inspection.

Common Mistakes to Avoid

• Too much pressure. The #1 DIY error. Verify 50 PSI (poly) / 80 PSI (PVC) on a gauge, not by feel.
• Blowing through a closed zone. Always confirm the zone valve is open before air flows.
• One marathon blow per zone. Long continuous air runs overheat components — use two shorter passes.
• Forgetting the backflow preventer. Blowing the lines but leaving the backflow full of water is a classic expensive mistake.
• Waiting until after the first freeze. By then the damage may already be done.
• Using a tiny compressor for a large system. If the compressor cannot maintain pressure, zones will not clear — rent a bigger unit or hire a pro.

When to Hire a Professional

• You do not know your pipe type or system layout.
• Your compressor cannot maintain adequate airflow.
• The system has no convenient blowout connection point.
• You are uncomfortable with any of the safety requirements above.
• You have a large system (many zones) or a complex setup with drip lines mixed in.

Professional blowout services are widely available in fall and are usually quick appointments. The cost is small compared to replacing split lines and valves in spring.

Frequently Asked Questions

Can I winterize my sprinklers without a compressor?

If your system has manual drain valves at all low points, you can drain it without air — open every drain valve and the backflow test cocks, and leave them open. It is less thorough than a blowout but adequate in milder freeze climates.

What PSI should I use for sprinkler blowout?

Maximum 50 PSI for polyethylene (black poly) pipe and 80 PSI for PVC pipe. When in doubt about your pipe type, use 50 PSI — lower pressure with adequate airflow still clears lines.

How long should I blow out each zone?

Until only air (no water mist) comes from the heads, plus about 2 minutes more — then a brief second pass on all zones. Avoid excessively long continuous runs.

Do I need to winterize drip irrigation lines too?

Yes — drain or blow out drip lines, remove and store filters, pressure regulators, and timers/faucet timers indoors. Drip emitters and thin tubing are very freeze-vulnerable.

Should I turn off the sprinkler controller for winter?

Leave it powered (so it keeps its program and clock) but set to Off or Rain mode. If the controller is in an unheated garage, that is fine — the electronics tolerate cold; it is water inside pipes and valves that causes damage.

What happens if I skip winterizing one year?

You might get lucky in a mild winter — or you might discover cracked pipes, split valves, and broken heads at spring startup. The repair cost almost always exceeds the cost of winterizing, whether DIY or professional.

Understanding Your System’s Key Components

Knowing what each part does helps you winterize thoroughly and spot problems:

• Main shutoff valve: isolates the irrigation system from the house water supply. Usually a ball or gate valve in the basement, crawl space, or an underground valve box.
• Backflow preventer: the brass assembly (often above ground near the house) that stops irrigation water from flowing back into your drinking water. It has test cocks (small screw valves) that must be drained — it is the most expensive single component to replace if it freezes and cracks.
• Zone valves: electric valves (usually in underground valve boxes) that the controller opens one at a time. Each controls one zone of sprinkler heads.
• Sprinkler heads: pop-up rotors and spray heads. Water trapped in the head bodies and the lateral lines feeding them is what the blowout clears.
• Controller/timer: the electronic brain. It holds no water, so it needs no draining — just set it to Off/Rain mode for winter.
• Drip zones: if your system includes drip irrigation, remember its filters, pressure regulators, and emitters need draining too — and remove any battery-powered hose timers to store indoors.

Spring Startup: Reversing the Process

Winterizing is only half the cycle. When freezing danger has passed in spring:

1. Inspect first: walk the system and look for heads damaged over winter, cracked valve box lids, or shifted components.
2. Close all drains and test cocks you opened in fall.
3. Pressurize slowly: open the main shutoff valve gradually — a sudden full-pressure surge can damage components (this is called water hammer protection in practice).
4. Run each zone manually and watch every head: look for geysers (broken heads or pipes), weak spray (clogged nozzles), tilted heads, and leaks at valve boxes.
5. Check the backflow preventer for leaks at the test cocks and seals — freeze damage often shows up here first.
6. Reset the controller from Off/Rain mode to your watering program, and adjust the schedule for spring conditions (less water than midsummer).
7. Flag anything suspicious for repair before the hot season — spring is when irrigation pros are least backlogged.

Related Guides

• How to Winterize Outdoor Faucets (Prevent Frozen Pipes)
• Where Is My Main Water Shutoff Valve?
• Fall Home Maintenance Checklist (32 Tasks)
• Leaky Outdoor Faucet? How to Fix It (Hose Bib Repair) — fixing a leaky outdoor faucet.