Winterize sprinkler system

Blow out your sprinkler system before freezing temperatures to prevent costly pipe damage.

Why it matters#

Water left in irrigation lines freezes, expands, and cracks pipes and fittings. Repair costs can run $500-1,000+. Winterizing takes an hour and costs nothing (DIY) or $50-100 (pro).

What you'll need#

Tools#

• Air compressor (10+ CFM, capable of sustained output)
• Air hose with blowout adapter
• Flathead screwdriver

Steps#

1. Schedule before the first hard freeze#

Watch the forecast. Winterize when nighttime temps will consistently drop below 32°F. In most northern climates, this is October.

2. Turn off the water supply#

Locate and close the main irrigation shutoff valve. This is typically inside your house or in a basement.

3. Drain the backflow preventer#

Open the test ports on the backflow preventer with a flathead screwdriver to release water. Leave them cracked open for winter.

4. Connect the air compressor#

Attach your compressor to the blowout port (usually on the backflow preventer or main valve). Use a quick-connect fitting designed for this purpose.

5. Set the correct pressure#

Adjust the regulator: maximum 50 PSI for PVC pipes, 80 PSI for polyethylene. Higher pressure can damage the system.

6. Blow out one zone at a time#

Activate a zone at the controller. Let the compressor blow air through until only a fine mist (no solid water) comes from the heads—usually 2-3 minutes.

7. Don't overheat the pipes#

Wait 1-2 minutes between zones to prevent heat buildup from compressed air. Run each zone twice to ensure complete clearing.

8. Repeat for all zones#

Work through every zone in your system. Don't skip any—one missed zone can crack over winter.

9. Open backflow valves to 45 degrees#

Turn the ball valves on the backflow preventer to a 45-degree angle (halfway between open and closed) so any remaining water can escape.

10. Shut down the controller#

Set the controller to "Rain" mode or turn it off. Remove backup batteries for winter to prevent drain and leakage.

Pro tips#

• Hire a pro if you don't have the right compressor—improper equipment is the #1 cause of DIY blowout failures
• Mark your calendar to do this at the same time every year
• If you see water still spraying forcefully after 3 minutes, your compressor may not have enough CFM
• Some zones (especially uphill runs) may need extra blowout time

Warnings#

• Too much pressure (over 50-80 PSI depending on pipe type) can crack pipes and damage heads
• Don't run the compressor continuously for more than 3 minutes per zone—compressed air heats up and can melt fittings
• Never blow out a zone with no heads open—this creates dangerous pressure buildup

When to call a pro#

Consider hiring a professional ($50-100) if: you don't own a sufficiently large compressor (10+ CFM), you're unsure of your pipe material, you have a complex system with many zones, or you want guaranteed protection. The cost is far less than repairing freeze damage ($500-1,000+).