How to winterize the sprinkler system
To winterize a sprinkler system, shut off the irrigation water before the first hard freeze, then clear the lines by draining them or blowing them out with compressed air. Keep air under 80 PSI for PVC and 50 PSI for polyethylene, and never blow air through the backflow device. A pro typically charges about $59 to $144.
When and how to winterize a sprinkler system
Winterize once a year in any area with freezing nights. LawnStarter suggests finishing as overnight lows approach 32°F, and says a week early beats a day late. Shutting down early won't hurt the lawn. Skipping the job can mean hundreds of dollars or more than $1,000 in freeze repairs.
| Method | When it fits | What it involves |
|---|---|---|
| Manual drain | Your system has manual valves at the low and end points of the pipe | Shut off the water and open the drain valves |
| Automatic drain | Your system has automatic drain valves | Shut off the water and run a zone to release the pressure |
| Air blowout | Other systems, and where you want the lines fully cleared | Push compressed air through each zone |
Colorado State University Extension doesn't trust gravity drains and calls compressed air the only reliable way to clear a system. Hunter lists all three methods. If your installer left notes, follow the design of your system.
What you need to blow out sprinklers
- The location of your irrigation shutoff, often in the basement in cold climates
- A flathead screwdriver for test cocks
- ANSI-approved safety eye protection
- For a blowout: a rented compressor, a hose and a fitting downstream of the backflow device
Hunter calls for a compressor rated at 80 to 100 CFM on mainlines of 2 inches or less. A small shop compressor is unlikely to keep up. Colorado State's sizing rule is each zone's flow in gallons per minute, divided by 7.5.
How to winterize a sprinkler system, step by step
- Shut off the irrigation water
Close the irrigation shutoff, which is usually a gate, globe, ball or stop-and-waste valve.
- Set the controller
For an outdoor controller, leave the power on and the dial at Off. The transformer's warmth limits condensation. Indoor models can stay on Off or be unplugged.
- Drain, or set up for a blowout
For a drain system, open the manual valves and let the mainline empty. For a blowout, connect the compressor after the backflow device with its valve closed.
- Blow out one zone at a time
Start at the zone farthest from the compressor and open the air slowly. Stay under 80 PSI for PVC and 50 PSI for polyethylene. Never stand over pipes, heads or valves.
- Stop when each zone runs dry
This takes about two minutes or more per zone. Two or three short cycles beat one long one. Air in a dry pipe creates friction heat that can cause damage.
- Drain the backflow device
Disconnect the air. Work the isolation valves open and closed a few times, leave them at about 45 degrees, and open the test cocks.
- Close up and protect
Close any manual drain valves after a blowout. Empty a cup-style rain sensor, cover it, and insulate an exposed backflow device. Keep pets inside during the job, because the whistling can startle them.
Freeze damage to look for after you winterize sprinklers
Look for these when you turn the system on in spring:
- Water pooling between cycles, which can mean an underground leak
- Sprinkler heads that don't pop up fully or sit tilted
- Valves that seep when the system is off
- A cracked backflow body, or water spraying from it. Shut off the supply and call a licensed pro.
Winterize sprinklers yourself or hire a pro for the blowout?
Hunter recommends a qualified licensed contractor for blowouts. Compressed air can throw debris and cause serious eye injury, and too much pressure can damage the pipe. Check any installer warranty before you do it yourself, because DIY work may void it. LawnStarter suggests paying a pro once while you watch, then deciding about next year.
Backflow devices protect your drinking water, and the rules on them are local. Ask your water district or building department what's allowed, and how a device should be tested and drained. Colorado State says pressure vacuum breakers and reduced pressure devices must never be blown out, because their rubber seals can melt.
Sprinkler blowout questions
How much does it cost to winterize sprinklers?
LawnStarter puts professional winterization at about $59 to $144. Renting a compressor runs about $32 to $55 a day. Prices vary by region and system size.
What PSI should I use to blow out sprinklers?
Hunter's limit is 80 PSI for PVC pipe and 50 PSI for polyethylene pipe. Stay below the rating of your lowest-rated component.
Do I need to blow out sprinklers if I have drain valves?
Not always. Hunter lists manual and automatic drains as valid methods where a system is built for them, though Colorado State University Extension prefers compressed air. Ask your installer or a local irrigation pro.
Sources: redesign.hunterindustries.com, extension.colostate.edu, lawnstarter.com
General guidance for U.S. homes, not professional advice. For gas, electrical and structural work, call a licensed pro.