How to Winterize a Sprinkler System Using the Blow-Out Method: PSI Settings, Zone Sequence & Backflow Preventer Drain Steps

How to Winterize a Sprinkler System with the Blow-Out Method

Failing to properly winterize your sprinkler system before freezing temperatures arrive can lead to cracked pipes, damaged valves, and costly repairs come spring. The blow-out method uses compressed air to force residual water from every line and sprinkler head, and it remains the most reliable winterization technique for the majority of residential and commercial irrigation systems. This step-by-step guide covers everything you need: recommended PSI settings for different pipe types, the correct zone-by-zone sequence, and how to properly drain your backflow preventer to protect it from freeze damage.

What You Will Need

• Air compressor capable of producing 80–100 CFM (cubic feet per minute) for larger systems or 20–30 CFM for smaller residential systems- Compressor-to-irrigation adapter fitting (typically a quick-connect coupler to garden hose thread)- Safety glasses- Flat-head and Phillips screwdriver- Adjustable wrench- Towels or rags for the backflow preventer drain

Step-by-Step: Blow-Out Winterization Process

Step 1: Shut Off the Water Supply

Locate the main irrigation shut-off valve. This is typically found in the basement, crawl space, or mechanical room near the water meter. Turn it fully clockwise to close it. If your system has a separate curb stop or meter shut-off for irrigation, close that as well.

Step 2: Connect the Air Compressor

Attach the compressor hose to the blow-out port on your irrigation system. This port is usually located downstream of the backflow preventer and may have a threaded fitting or quick-connect. Ensure the connection is tight and secure. Do not turn on the compressor yet.

Step 3: Set the Correct PSI

Proper air pressure is critical. Too much pressure will damage pipes, fittings, and sprinkler heads. Too little will leave water behind that can freeze and crack components. Use the following PSI guidelines:

Step 4: Blow Out Zones in the Correct Sequence

The order in which you blow out zones significantly affects how thoroughly you remove water. Follow this procedure:

• Start with the zone farthest from the compressor connection point. This zone has the longest pipe run and requires the most sustained airflow to clear completely.- Open one zone at a time using your irrigation controller set to manual mode or by manually engaging each zone valve. Never blow air through the system with all valves closed—this creates dangerous pressure buildup.- Run the compressor for each zone for approximately 2–3 minutes, or until no more water or mist is visible coming from the sprinkler heads. Watch the heads carefully—when you see only dry air, that zone is clear.- Allow the compressor to recover between zones. Shut off the airflow, let the tank refill to operating pressure, then move to the next zone.- Work sequentially toward the zone closest to the compressor. This ensures upstream lines are the last to be cleared.- Repeat each zone a second time with a brief 30-second burst to catch any residual water that may have settled after the first pass.Warning: Never run the compressor with no zones open. Never stand directly over sprinkler heads during blow-out. Debris and water can be ejected at high velocity.

Step 5: Drain the Backflow Preventer

The backflow preventer is one of the most freeze-vulnerable components in your irrigation system. Draining it properly is essential. Follow these steps:

• Close both shut-off valves (the inlet valve upstream and the outlet valve downstream of the backflow preventer). Turn each handle perpendicular to the pipe so they are fully closed.- Open the test cocks. Most backflow preventers have two small test cocks (petcocks) located on the body of the device. Using a flat-head screwdriver, turn each test cock to the 45-degree open position (halfway between fully open and fully closed). Water will drain from these ports—have towels ready.- Open the bleeder valves or relief valve if your preventer is equipped with them. On pressure vacuum breakers (PVBs), pull the bonnet or poppet up to release trapped water. On reduced pressure zone (RPZ) assemblies, open the relief valve drain.- Leave the test cocks in the 45-degree position all winter. This allows any residual moisture to escape and prevents pressure buildup from temperature fluctuations.- If your backflow preventer is above ground, consider wrapping it with an insulated cover or bag designed for freeze protection as an extra precaution.

Step 6: Open Manual Drain Valves

If your system has manual drain valves at low points in the piping, open them after the blow-out to release any remaining water that may have pooled. Leave these valves open through the winter.

Step 7: Set the Controller to Rain Mode or Off

Turn your irrigation controller to the “Rain” or “Off” position. Rain mode is preferred because it keeps your programmed schedules and settings in memory while preventing any zones from running. If your controller has a backup battery, check that it is fresh so your programming is retained through winter.

Common Mistakes to Avoid

• Exceeding recommended PSI: Over-pressurizing is the number one cause of blow-out damage. Cracked PVC fittings and shattered sprinkler head internals are expensive to repair.- Using a pancake or small shop compressor: Most small compressors produce only 2–4 CFM. They cannot move enough air volume to clear irrigation lines. Rent a commercial compressor rated for at least 20 CFM.- Forgetting the backflow preventer: This is the single most expensive component. Skipping its drain procedure almost guarantees freeze damage.- Blowing out all zones simultaneously: This splits airflow across too many paths and fails to adequately clear any zone.

Frequently Asked Questions

What size air compressor do I need to winterize my sprinkler system?

For most residential systems with up to 8 zones, a compressor rated at 20–30 CFM and capable of maintaining 50–80 PSI is sufficient. Larger commercial systems may require 80–100 CFM. Volume (CFM) is more important than pressure (PSI). Small workshop compressors typically lack the CFM needed—renting a towable or large portable compressor from a tool rental center is usually the best option and costs between $50–$100 per day.

Can I winterize my sprinkler system myself, or should I hire a professional?

You can absolutely winterize your system yourself if you have access to an adequate compressor and follow proper PSI guidelines. The process typically takes 30–60 minutes. However, if you are uncomfortable working with pressurized air, are unsure of your pipe material, or have a complex system with a reduced pressure zone backflow preventer, hiring a licensed irrigation professional is a worthwhile investment. Professional winterization typically costs $75–$150 depending on system size and location.

When is the right time to winterize a sprinkler system?

Winterize your system before the first hard freeze, which is defined as when air temperatures drop to 28°F (−2°C) or below for more than four consecutive hours. In most northern U.S. climates, this means scheduling your blow-out between mid-October and early November. Check your local frost date averages and plan for at least one week before the expected first hard freeze to allow a buffer for unexpected early cold snaps.