Sprinkler systems are designed for above-freezing operation. Once cold weather arrives, the water sitting in pipes, valves, and heads becomes a system-wide hazard. A 30 to 60 minute winterization in early fall protects every component for the entire winter. This guide covers the right compressor sizing, the order to blow zones, what to do at the backflow preventer, and a few common mistakes that turn winterization into the source of damage rather than the prevention.
Why water in sprinklers is a problem
Water expands by about 9 percent when it freezes. The expansion happens with enormous force, far more than the burst pressure of any plastic or metal pipe used in residential irrigation. PVC pipe cracks at 100 PSI of overpressure; freezing water generates thousands of PSI of expansion force as it converts to ice.
The damage hierarchy from least to most expensive:
- Sprinkler heads: 5 to 15 dollars each, usually visible from above
- Valve diaphragms: 30 to 60 dollars per valve, requires excavating the valve box
- Backflow preventer: 100 to 400 dollars, often the most expensive single failure
- Underground PVC lateral pipes: 200 to 800 dollars per repair, requires digging up the line to find the crack
- Main supply line under the foundation: thousands of dollars for major repair
Winterization addresses all of these by removing the water before the freeze.
Tools and materials
For DIY winterization plan for:
- Air compressor sized for your system (see CFM guidance below)
- Pressure regulator (most compressors have one built in)
- Quick-connect compressor coupling
- Adapter to connect compressor to the sprinkler blowout fitting (typically 3/4 or 1 inch quick-connect to garden-hose-thread)
- Safety glasses
- A second person to monitor zone heads during blowout
Critical sizing: the compressor needs to deliver enough air volume to clear the largest single zone in your system. A small homeowner compressor (2 to 4 CFM) cannot keep up with a typical 8 to 12 head zone. Rent a 5 to 10 CFM tow-behind or wheelbarrow compressor for the day if your home compressor is undersized.
Pressure regulation: 50 PSI max for poly lateral lines, 80 PSI max for all-PVC systems. Most residential systems are mixed, so 50 PSI is the safe choice.
Shutting off the water supply
Locate the main shutoff for the sprinkler system. It is usually a dedicated ball valve near where the irrigation line branches from the main household water line. Some systems have the shutoff inside the basement or crawlspace; others are in a valve box near the meter.
Close the shutoff fully. Then open a sprinkler head or test valve on the irrigation side to relieve any residual pressure. The pressure should drop to zero within a few seconds.
Connecting the compressor
Most residential sprinkler systems have a blowout adapter on the irrigation manifold, downstream of the backflow preventer. The adapter is typically a 3/4 inch threaded fitting capped with a quick-connect or hose-thread cap. Remove the cap.
Connect the compressor hose to the adapter using the right adapter for your fitting. Hand-tighten only; do not overtighten as the fittings are usually plastic and can crack.
Set the compressor regulator to the safe pressure for your pipes (50 PSI for poly, 80 PSI maximum for PVC).
Do not connect the compressor upstream of the backflow preventer. The backflow contains a check valve that holds water back, and air pressure on the wrong side can damage the internal seals.
Blowing out the zones
With the compressor running and connected, manually activate the first zone at the controller. The compressor air pushes water out of the lateral pipe through the sprinkler heads in that zone.
Watch the heads. At first, water shoots out, then a mix of water and air, then mostly air with mist. Stop the zone once the heads are blowing dry air, typically 2 to 5 minutes per zone. Running a single zone too long without water flowing causes the heads to overheat from the friction of compressed air, which damages the seals.
Move to the next zone. Repeat through all zones. After all zones have been blown once, repeat the cycle one or two more times in the same order. Water keeps weeping out of low points in the pipes and accumulates between cycles. Three passes typically remove enough water to prevent freeze damage.
Pay attention to the highest and lowest zones in the yard. The lowest zone often holds the most water because water flows downhill to it during normal operation. The highest zone may need extra time because the compressor has to overcome the elevation head.
Backflow preventer
The backflow preventer (typically a pressure vacuum breaker or double check valve assembly) sits between the house water and the irrigation system. After the zones are blown out, the backflow needs its own treatment.
For pressure vacuum breakers (PVBs) above ground:
- Close both shutoff valves on the assembly
- Open both bleed petcocks at the top of the assembly
- Open both test cocks on the side of the assembly
- Allow all water to drain out
For double check valve assemblies:
- Close both shutoff valves
- Open all four test cocks
- Allow all water to drain
In freeze-prone regions, also insulate the backflow assembly with a fitted foam cover or rags inside a plastic bucket for additional protection.
Controller and valves
At the controller, set the system to off or rain mode for the winter. Some controllers have a winter setting that suspends scheduled watering automatically. Leave the controller plugged in to retain the schedule, or unplug it and accept that you will need to reprogram in spring.
Valve manifolds typically self-drain through the blowout process. Manifolds with manual drains should be opened after the final blowout pass. Close them again before the controller is brought back online in spring.
Common mistakes
Using a small compressor and assuming it worked: a 2 CFM compressor takes 15 to 20 minutes to clear a single zone properly, and most homeowners give up after 3 to 5 minutes thinking the zone is dry. Water remains in low spots. The correct compressor finishes a zone in 2 to 5 minutes with confidence.
Blowing pressure too high: exceeding 80 PSI on PVC or 50 PSI on poly damages the heads, valve diaphragms, and pipe fittings. The damage from over-pressure winterization is often blamed on winter freeze damage the following spring.
Skipping the backflow drain: the backflow assembly is the most expensive single component in most residential sprinkler systems. Frozen water in it cracks the brass body. Replacement costs 100 to 400 dollars. Draining takes 30 seconds.
Forgetting the controller in spring: when bringing the system back online in spring, check valve and head functionality before walking away. A single cracked fitting can leak underground for days before showing up as a wet spot on the lawn.
See the methodology page for our irrigation evaluation approach. Pair this guide with the outdoor faucet installation article and the french drain installation guide for a complete outdoor water management sequence.
Frequently asked questions
Do I really need to winterize my sprinkler system?+
In any region where the ground freezes (typically anywhere with average winter low temperatures below 25F), yes. Water expands by about 9 percent when it freezes. Water sitting in PVC sprinkler pipes, backflow preventers, valve manifolds, or sprinkler heads will rupture those components when it expands. Repair costs run 200 to 1500 dollars in spring depending on what cracked. In mild climates (USDA zones 9 and 10), winterization is optional but draining low points is still recommended. Drip irrigation systems with above-ground tubing need winterization in any climate where freezes occur.
Can I winterize sprinklers myself or do I need to hire it out?+
DIY is feasible if you have access to a 5 to 10 CFM air compressor and understand your system layout. Rental costs about 50 dollars per day at a tool rental shop. Pro winterization runs 75 to 150 dollars per visit and uses larger truck-mounted compressors that finish faster. For DIY, the limit is compressor capacity. A typical pancake or hot-dog homeowner compressor (2 to 4 CFM) is not enough air volume to clear the lines properly. Rent the right size or hire it out. Skip this and the blowout misses zones, leaving water in pipes.
What air pressure should I use to blow out sprinkler lines?+
Maximum 80 PSI for PVC pipes and 50 PSI for polyethylene (poly) pipes. Higher pressure damages sprinkler heads, splits poly fittings, and can crack PVC at threaded joints. Most residential systems use a combination of PVC main lines and poly lateral lines, so 50 PSI is the safe upper limit. Volume (CFM) matters more than pressure for clearing water. Use a regulator on the compressor output to cap pressure at the appropriate level for your pipe material. Higher pressure does not blow lines clearer; it just damages parts.
How many CFM does my compressor need to winterize sprinklers?+
Minimum 5 CFM for small systems (3 to 5 zones). 8 to 10 CFM for medium residential (6 to 10 zones). Truck-mounted compressors used by pros deliver 25 to 50 CFM. CFM (cubic feet per minute) is the volume of air the compressor can deliver continuously. Pressure (PSI) just sets the force; CFM determines how much water the air can push out per minute. A small 2 CFM compressor cannot move enough air to clear a 3/4 inch lateral pipe before the tank empties. Rent appropriately or the blowout misses water.
When should I winterize sprinklers - what is the timing?+
Winterize 2 to 4 weeks before the first hard freeze in your area, typically late September to mid-October across most of the northern US. Watch the 10-day forecast. Plan to winterize before any forecast night below 28F. Earlier than 4 weeks before first freeze is fine if convenient. Later than first freeze risks already-frozen water during the blowout, which can crack the pipes during winterization itself. If you missed the window and a hard freeze is forecast within 24 hours, shut off the water at the backflow and accept that some components may have already taken damage.
