Frozen water expands 9% in volume. Inside a sealed pipe, that expansion creates pressures exceeding 2,500 PSI — far beyond what any irrigation component can withstand. The result is cracked PVC, shattered valve bodies, broken backflow preventer casings, and split sprinkler heads.
Repair costs range from $200 for a single broken head. A fractured manifold with trenching runs $3,000+.
When to Start Winterizing
Begin before the first hard freeze. Most US zones need winterization between late October and early November. Your USDA Hardiness Zone determines the exact timing.
If you wait until after freezing temps hit, water already trapped in your lines expands. That expansion cracks something.
Repair cost $420 in plumbing. Starting early gives you room to fix mistakes.
Warning signs you need to winterize immediately
- Air temperature forecast drops below 32°F (0°C) within 48 hours
- Your last growing season ended and plants are dormant
- You haven’t winterized in more than 12 months
- Visible frost on above-ground pipes or backflow preventers
Step 1: Shut Off the Main Water Supply
Locate your system’s main shut-off valve. This is typically a ball valve on the supply line before your backflow preventer. Turn it clockwise until it stops — usually half a rotation from fully open.
If your system connects to a municipal water line, there may also be a separate isolation valve at the meter box. Close that too. Always double-check by turning on any zone from the controller and confirming no water flows from the sprinkler heads. If water still comes out, your main shut-off isn’t fully closed or there’s a cross-connection somewhere.
Step 2: Drain Above-Ground Components
Water in exposed pipes freezes and expands. A one-inch PVC pipe holding just two gallons of water exerts roughly 1,200 pounds of force when it freezes — enough to crack pipe walls, fittings, and valve bodies.
Disconnect all hoses from outdoor faucets and system drain ports. Open the drain valves on your backflow preventer if it has them. Most standard RP (Reduced Pressure) backflow assemblies have two drain cocks at the bottom — turn each 90 degrees with a screwdriver and let gravity do the work. Expect 2-5 gallons of drainage depending on system size.
If your backflow preventer is above ground (common in colder climates), wrap it in foam insulation after draining. You can buy backflow preventer wraps for $15 at any hardware store. Closed-cell foam pipe insulation cut to length works too.
Step 3: Blow Out Your Sprinkler Lines
This step causes the most DIY damage. The goal is to push residual water out of every zone using compressed air.
Equipment you need
- Air compressor: minimum 100 CFM at 40-80 PSI. A 30-gallon tank compressor from Home Depot costs $300-400. That handles most systems up to 12 zones.
- , Hunter BL-808, ~$25)
- Pressure gauge rated to at least 150 PSI
- Safety goggles and ear protection
The golden rule: never exceed 50 PSI for PVC, 80 PSI for polyethylene
PVC pipe rated for irrigation is Schedule 40. Stress appears above 50 PSI during blow-outs. Polyethylene (poly) pipe handles up to 80 PSI.
Watch the regulator gauge on your blow-out kit. The tank gauge lies.
Blow-out procedure for each zone
- Connect the blow-out adapter to the system’s test port or the first zone’s valve manifold
- Set compressor regulator to 40-45 PSI (PVC) or 60-70 PSI (poly)
- Activate one zone at a time from the controller — never blow out all zones simultaneously
- Watch each sprinkler head. Run it until only mist comes out (usually 30-90 seconds per head)
- Fixed spray heads: 30-45 seconds per station
- Rotors (multi-stream): 90-120 seconds per station
- Move to the next zone. Repeat until all zones are clear
If your system has a drip irrigation zone, do not blow it out with compressed air . Drip tubing and emitters are rated for 15-30 PSI maximum. Drain drip zones by opening end caps and letting gravity drain, or use a dedicated low-pressure drip blow-out adapter with a 15 PSI regulator.
Step 4: Insulate Exposed Components
After blowing out, insulate anything above ground that holds residual moisture:
- Backflow preventer: Foam wrap or insulated cover ($15-25). Remove in spring.
- Valve manifold: Wrap valve boxes with burlap or insulated covers. Don’t seal them airtight — condensation traps moisture.
- Above-ground pipes: Cut foam pipe insulation to length and tape seams with duct tape.
- Controller: Leave indoor controllers unplugged or set to rain/frost mode.
Step 5: Set Your Smart Controller to Rain/Frost Mode
), switch it to frost or rain mode before winter. This pauses all watering schedules automatically. The Rachio 3 detects frost via GPS weather data and won’t run if temperatures drop below 38°F.
The controller remembers all zone run times and settings — you don’t need to reprogram anything in spring.
How Long Does Winterizing Take?
A complete winterization takes 2-4 hours for a standard residential system:
- Shut off water and drain backflow: 15 minutes
- Disconnect hoses and open drain valves: 10 minutes
- 5-2 hours for 8-12 zones
- Drain drip zones separately: 30 minutes
- Insulate exposed components: 20 minutes
- Set controller to frost mode: 5 minutes
Larger systems with 15+ zones take 4-6 hours. If you hire a professional, expect to pay $150-400 depending on system size. The DIY route costs $300 for a compressor rental plus your time.
Choosing the Right Air Compressor
CFM matters more than PSI. Your compressor needs to move enough air volume to push water out of long runs of pipe.
- Under 6 zones: 20-gallon pancake compressor ($150-200). Adequate for short PVC runs.
- 6-12 zones: 30-60 gallon vertical tank ($300-600). Sweet spot for most homes.
- Over 12 zones: Rent a 175 CFM+ gas-powered compressor ($80-120/day).
Spring Reactivation Checklist
When temperatures consistently stay above 45°F (typically March-April), begin spring activation slowly. Rushing this process causes damage.
- Remove all insulation from backflow preventers and exposed pipes
- Open the main water supply slowly — quarter turns, 10 minutes apart
- Manually activate each zone to check for damage
- Look for geysers (broken heads), pooling water (cracked pipes), or zones that won’t pressurize
- Test your backflow preventer — have it certified if your municipality requires annual testing
- Reset your smart controller schedule based on current seasonal needs
- Adjust sprinkler head heights — winter settling often buries heads below grade
Practical guidance:
Winterizing your own irrigation system takes one Saturday morning and about $300 if you rent a compressor. The savings versus hiring a pro ($200-400) justify the effort for most homeowners. But don’t rush the blow-out.
Go zone by zone, watch the pressure gauge like a hawk, and never exceed 50 PSI on PVC. Your system will thank you next spring.
One final tip: take photos of your system before winterization. Document valve locations, backflow preventer type, and controller settings. These photos save hours of troubleshooting in spring.
