Awaiting expert review. This page covers safety or regulatory rules that change over time. It is kept out of search results until a qualified reviewer has checked it; the sources below are dated so you can verify each point.
Quick answer
Irrigation system winterization is the process of removing water from sprinkler pipes, valves, heads and backflow devices, usually by gravity drains or compressed air, so freezing water cannot expand and crack them.
Colorado State Extension calls compressed air the only reliable method it describes, and Medford Water says a system is not free of freeze risk while any water remains. Compressed air is also the step that can hurt people and parts, so it belongs with a licensed irrigation contractor.
Quick facts
The key facts about Irrigation System Winterization, with sources:
- What freezing does
- Water that freezes expands inside sprinklers, pipes and valves and can break them 3
- Colorado State view
- Compressed air is the only reliable method described; do not trust manual or automatic drain valves 1
- Backflow devices
- Pressure vacuum breakers and reduced pressure devices must never be blown out with compressed air 1
- Backflow testing
- Colorado State says devices must be certified at installation and at least annually by a certified tester 2
Key takeaways
- The goal is empty pipes, valves and backflow devices before water inside can freeze. Freezing, not cold itself, does the damage.
- Three methods exist: manual drains, automatic drains and compressed air. Sources disagree on how much to trust the drain valves.
- Compressed air carries real injury and equipment risk. Pressure, air volume and zone time all matter, and sources print different numbers.
- Backflow devices are the most freeze-sensitive part, and the rules for them differ from the rules for the pipes.
- This page gives no step-by-step blowout. It shows what the sources say and what to ask a licensed irrigation contractor.
Winterization: emptying a system that was built to be full
A sprinkler system holds water in buried pipe, at valves and inside each head. In a hard freeze that water turns to ice and expands.
Medford Water puts it plainly: damage occurs when water freezes and expands inside sprinklers, pipes and valves 3.
Colorado State Extension adds that pipes, fittings, valves, sprinklers and pumps can all crack or burst 1.
Winterization removes that water. The goal is not zero risk. Medford says a system is not completely free of the risk of freezing as long as any water remains, and describes draining more than half the water as a general rule of thumb, not a finish line 3.
Whether you need it depends on whether your ground freezes. This page owns the winterization idea and the method comparison. For the controller you will shut down for winter, see irrigation controllers. For what the system does the rest of the year, see irrigation services.
Spring startup is the other half. Colorado State notes that backflow ball valves should be opened slowly in spring to avoid water hammer damage 1.
The three drain methods and what each source says
| Method | How it works | What the sources say | Where it falls short |
|---|---|---|---|
| Manual drain valves | Valves at low points of the main line let water run out by gravity 5 | Rain Bird’s newsletter describes it as a method and says the main-line drain must sit at the lowest point 5. Colorado State says not to trust manual or automatic drains 1 | Remote control valves keep water inside unless disassembled or blown out 5. Colorado State cites pipe shift and no visual check 1 |
| Automatic drain valves | Spring-loaded drains at low points open whenever the system is shut off 5 | Rain Bird says never install them on a main line and says a stuck-open drain shows up as puddling 5. Colorado State says not to trust them 1 | Same limit for remote control valves; heads with built-in check valves must be disassembled or blown out 5 |
| Compressed-air blowout | A compressor pushes water out zone by zone 41 | Colorado State calls it the only reliable method it describes. Medford Water calls it the best method but notes many local systems are not equipped 13 | Injury risk, damage from too much pressure and low-volume air riding over water 14 |
Sources disagree, and that is information
The Rain Bird newsletter treats gravity drains as valid methods when a system is built for them. Colorado State says not to trust them.
The IANY article says manual-only gravity methods may produce poor results 4. Which one fits your system depends on how it was designed, which a contractor can read from the layout.
How a professional winterization visit is organized
The list below is the order of a visit, so you know what to expect. It is not a procedure for you to run. Each source prints its own details, and the numbers differ.
- Planning. The contractor identifies the valve type, pipe material, backflow device and any pump. Colorado State separates pump and controller steps from pipe steps 1.
- Water off. The system supply is shut off, and drains or the compressor connection are set as the maker directs. Medford says the backflow valve must not serve as the main shut-off 3.
- Air, zone by zone. Colorado State says to blow out one zone at a time and each zone twice in short cycles 1. Rain Bird’s IANY article says no circuit more than two minutes at a time 4.
- Backflow device. Per Colorado State, vacuum breakers and reduced pressure devices are drained and left with ball valves part open, and never blown out with air 1.
- Controller and pump. Colorado State says to keep the controller powered. Medford says to disconnect the common wire instead of unplugging. Pumps come out or are drained and insulated 13.
- SurveyValves, pipe, backflow device, pump
- Water offSupply shut, not via the backflow valve
- Clear the zonesDrains or air, one zone at a time
- Protect the backflow deviceDrain it, set ball valves, insulate
- Park the controllerAs the maker and contractor direct
Order of work drawn from Colorado State Extension fact sheet 4.719 and Medford Water. A guide to what to expect, not instructions. Source: [1] [3]
Compressed air can injure people and break the system
Colorado State says to wear proper eye protection. Medford Water says never stand over or near any sprinkler or valve while a compressor is running, never run a compressor without an open valve, and warns that uncontrolled high air pressure may blow system parts apart 13.
Rain Bird’s IANY article says some manufacturers do not approve compressed air and will not warrant damage from it 4. Use a licensed irrigation contractor.
Example: comparing what three sources print about air
The table shows what each source prints and for what. It is not a recommended setting. Each source describes a different setup, and none replaces your equipment’s rating or a contractor’s judgment.
| Source | Compressor pressure it prints | Air volume it prints | Other limits it prints |
|---|---|---|---|
| Colorado State Extension (fact sheet 4.719) | 40 to 80 psi at the compressor | Divide the zone’s gallons per minute by 7.5 to get cubic feet per minute | 80 psi maximum for rigid PVC and 50 psi for polyethylene; one zone at a time; each zone twice in short cycles 1 |
| Medford Water (Oregon) | 50 psi as the compressor target | 60 to 100 cubic feet per minute for systems with 2-inch piping and smaller | Station run times of 2 to 3 minutes; ANSI-approved eye protection 3 |
| Rain Bird author, IANY article (2007) | 50 to 80 psi, regulator set to 50 psi | 100 to 160 cubic feet per minute | No circuit more than two minutes at a time; do not pressurize a closed main line 4 |
Three sources, three different volume rules, and one pressure range that overlaps at 50 psi. That is the point.
Air volume and pressure depend on pipe size, material and zone size, and a contractor’s equipment is rated for it.
Use this table only to see why a small shop compressor is a poor fit, as Rain Bird’s author says 4.
Where you meet the term: service lists, contracts and water bills
On a landscaping or irrigation service list. Fall closing, winterization and blowout often mean the same visit. Ask what the line includes: zones, backflow device and controller.
In a seasonal contract. A maintenance plan may include it. Read the scope in the lawn care contracts guide.
In a fall task list. Winterization appears beside leaf and bed work. Our fall yard cleanup entry lists the seasonal tasks, and the yard maintenance checklist shows how they fit the year.
From your water supplier. Utilities, such as Medford Water, publish winterizing guidance and sometimes a backflow testing program 3.
What winterizing protects, and what it cannot
What it protects
- Protects pipes, fittings, valves, sprinklers and pumps from freeze cracks 1.
- Protects backflow devices, which Colorado State says are damaged by freezing unless fully drained 2.
- Costs less in labor than repairs. Colorado State says it is much less costly and less labor intensive to prepare in the fall 1.
- Gives a chance to find leaks and stuck valves before spring.
What it cannot do
- Cannot guarantee zero water left. Medford says risk remains while any water remains 3.
- Does not fix a bad design. Low spots and flat runs can hold water regardless of method.
- Carries risk if done with air by someone without the equipment and training 13.
- Does not cover the backflow test. Colorado State says certification is separate and at least annual 2.
Limits and open points in the evidence
The sources do not agree on one set of numbers. Colorado State, Medford Water and the Rain Bird author give different pressure targets and air volumes, and for different pipe sizes and setups. That is why we print them side by side and give no single setting.
They also disagree on the controller. Colorado State says not to unplug it and to run it through a minimum cycle weekly to keep solenoid plungers from sticking 1.
Medford says to disconnect the controller’s common wire rather than unplug it 3. We cannot tell you which is right for your model. Follow the maker’s manual.
Colorado State’s fact sheet does not say who should do the work 1.
We found no national standard or code for winterization itself. The rules that exist are about backflow devices and local water programs, and they vary.
What changes the price of a winterization visit
We do not publish prices. A visit moves with the number of zones, pipe size and material, the type of valves, whether drains were built in, whether there is a pump or a backflow device that needs draining, and how far the crew must travel.
Medford notes that many local systems are not equipped for blowouts 3, which can change what a contractor needs to bring.
A separate backflow test is another line. Colorado State says devices must be certified at installation and at least annually by a certified tester 2. Ask whether the winterization price includes that or not.
Damage repair is the other cost. A cracked valve or a burst fitting is a repair visit. Colorado State frames winterizing as the cheaper route 1. For how bids are built, see the cost hub and the landscaping estimates guide.
No source gives a lifespan for a system that has been winterized. Do not assume one.
Who does it, and what to ask before the visit
A licensed irrigation contractor, or a backflow-certified technician for the device, is the safest choice for the air and the backflow steps. Use this list to prepare the conversation.
- Ask whether the crew uses compressed air, drains or both, and why that fits your system.
- Ask what compressor volume and pressure they use and how they set it for your pipe material. Do not ask them to follow a number you found online.
- Ask how they handle the backflow device. Colorado State says vacuum breakers and reduced pressure devices are never blown out with air 1.
- Ask who certifies the backflow device, and whether the test is separate 2.
- Ask what they do with the controller and pump, and whether it matches the maker’s manual.
- Ask for a written scope that lists zones, the backflow device and any re-check in spring. Our guide to choosing a company has more to put in writing, and licensing by state shows who is licensed where you live.
Never thaw a frozen pipe with an open flame, and call 811 before digging
Medford Water says never to thaw a frozen pipe with an open flame 3. If a repair needs digging, call 811 first. Do not open a backflow device or work on the supply line unless you are qualified; contamination of drinking water is the reason the devices exist 2.
Upkeep around winterization
Upkeep tasks are listed here without fixed dates. Your first hard freeze sets the timing, and your contractor or supplier can tell you when that is locally.
- Watch for puddles. Rain Bird says a stuck-open automatic drain shows as excessive puddling 5.
- Keep exposed parts protected. Medford says to insulate above-ground valves and to set backflow ball valves so they can drain 3.
- Open backflow ball valves slowly in spring. Colorado State says this prevents water hammer damage 1.
- Schedule the backflow test. Colorado State says at least annually 2.
- Run each zone in spring and look. Leaks, cracked heads and weak spray show up early.
Warning signs, and when to call a pro
- Water still comes out of low heads or valves after a blowout. Water remains, and freeze risk remains 3.
- A hiss or heads that did not pop up during air. Colorado State says heads that stay up while air flows are a rule of thumb for a right-sized compressor, so a contractor can read this sign 1.
- Cracked fittings or a geyser at a head in spring. Freeze damage. Shut off the supply and call a contractor.
- A backflow device with a damaged body. Colorado State says freezing damages devices that were not fully drained 2.
- Plastic parts hot to the touch during a blowout. Medford says to watch for overheating plastic parts 3. That is a stop-and-call-a-pro sign.
Any of these means stop and call a licensed irrigation contractor or plumber. Do not keep running air to see what happens.
Where the rules come from: standard, law and manual
| Kind | Authority | What it covers | What we verified |
|---|---|---|---|
| Manufacturer instructions | The maker of your controller, valves and backflow device | Whether compressed air is approved and warranty terms | Rain Bird’s IANY article says some manufacturers do not approve compressed air and will not warrant damage from it 4 |
| State or local backflow rules | Your water supplier, and in Colorado the state cross-connection program | Installation of backflow devices and at least annual certification | Colorado State says devices must be certified at installation and at least annually, and points to a Colorado state resource. No rule section was read 2 |
| Device legality | Local authority | Whether atmospheric vacuum breakers are allowed | Colorado State says they may not be legal in your area 1 |
| Winterization itself | None found | No national code or standard was found for the act of winterizing | Not verified; ask your water supplier or inspector |
Winterization vs. the jobs people mix it up with
| Job | What it is | What the sources say | Who usually does it |
|---|---|---|---|
| Irrigation winterization | Removing water from the system before freezing | Methods and limits above 13 | A licensed irrigation contractor for the air |
| Backflow device draining and testing | Protecting and certifying the device that guards drinking water | Devices must be certified at installation and at least annually in Colorado; freezing damages devices not fully drained 2 | A certified backflow technician |
| Spring startup | Refilling and checking the system | Open backflow ball valves slowly to prevent water hammer 1 | Contractor or owner, per the maker |
| Indoor pipe freeze protection | Heating, insulating and shutoff for house plumbing | Medford lists thermostat, insulation and shutoff steps for indoor plumbing 3 | Owner and a plumber |
| Fall yard cleanup | Leaf, bed and lawn tasks | Covered in the fall yard cleanup entry linked earlier | Owner or a landscaping company |
Common winterization myths
- Myth Opening the drain valves is enough.
- Reality Colorado State says not to trust manual or automatic drain valves. Rain Bird’s newsletter says remote control valves keep water inside unless disassembled or blown out 15.
- Myth A bigger compressor is always better.
- Reality Colorado State says larger compressors risk pressurizing too quickly and causing damage, and suggests a regulator 1.
- Myth Any small compressor will do.
- Reality Rain Bird’s author warns not to use a small shop compressor and try to cough the system clean. Air volume matters 4.
- Myth Blow air through the backflow device too.
- Reality Colorado State says pressure vacuum breakers and reduced pressure devices must never be blown out with compressed air 1.
The regional variable: whether and when your ground freezes
Winterization is a cold-climate task. The need depends on how often your area freezes and how deep, and on your supplier’s rules.
Medford Water in Oregon and Colorado State Extension both publish guidance for their own regions, and neither gives a national date 31.
Colorado State also points to a Colorado state resource for backflow testers 2.
Ask your local extension office or water supplier about freeze timing and backflow testing where you live, and do not rely on a calendar from another region.
When to winterize, and your next step
If your ground freezes, plan to winterize. If it never does, you may only need to protect exposed parts, and your supplier can say.
Your next step is to find out what you own: valve type, drains, pipe, backflow device, pump and controller model. Then book a licensed irrigation contractor, and, for the device, a certified backflow tester.
Ask for the scope in writing before the work. For other fall tasks, use the seasonal links above.
Questions about Irrigation System Winterization
What does it mean to winterize a sprinkler system?
It means removing water from pipes, valves, heads and backflow devices before it freezes, so expanding ice cannot crack them. The usual methods are manual drain valves, automatic drain valves and a compressed-air blowout. Colorado State Extension calls air the only reliable method it describes.
Why do sprinkler lines need to be blown out?
Gravity drains leave water in places, such as inside remote control valves. Colorado State says systems with electric valves must be blown out because water cannot otherwise drain from the top of the valve diaphragm. Rain Bird’s newsletter says valves must be disassembled to clear them unless air is used.
Can I winterize my sprinkler system myself?
Sources differ. Colorado State describes the process for homeowners but lists strict equipment and safety points. Rain Bird’s author stresses eye protection for contractors and homeowners. Because compressed air can injure people and break parts, we recommend a licensed irrigation contractor for the air and the backflow device.
What psi is safe to blow out sprinklers?
No single figure fits every system. Colorado State prints 40 to 80 psi at the compressor, with 80 psi the maximum for rigid PVC and 50 psi for polyethylene. Medford Water prints 50 psi. Your pipe, valves and heads set the limit, so a contractor should choose it.
Does it matter how much air the compressor delivers?
Yes. Colorado State says air volume is as critical as pressure, and Medford says blowouts depend on volume in cubic feet per minute. Low-volume air can pass over the water without clearing it. Sources print different volume rules, so equipment is a job for a contractor.
Should I blow air through my backflow preventer?
Not through the device. Colorado State says pressure vacuum breakers and reduced pressure devices must never be blown out with compressed air, because the rubber seals can melt from the heat. Medford says manufacturers advise against using test cocks for blowouts. A contractor or tester handles the device.
What do I do with the backflow device ball valves for winter?
Follow the maker and your contractor. Colorado State says to leave pressure vacuum breaker ball valves half open for winter and reduced pressure device isolation valves about 45 degrees open, because fully open or closed valves can trap water. Medford gives a similar 45-degree setting.
Should I unplug the sprinkler controller for winter?
Sources disagree. Colorado State says not to unplug it and to run a minimum cycle weekly so solenoid plungers do not stick. Medford says to disconnect the common wire rather than unplug. Follow your controller’s manual and ask your contractor what they do.
How often does a backflow preventer need testing?
Colorado State says backflow devices must be certified at installation and at least annually, and testing must be done by a certified technician. Rules differ by state and supplier, so ask yours which tester and schedule apply.
What if I miss the window and pipes freeze?
Shut off the supply and call a licensed contractor or plumber. Medford says never to thaw a frozen pipe with an open flame. Look for cracked fittings, valves and heads when thawing starts, and have backflow devices checked, since Colorado State says freezing damages those that were not fully drained.
Sources
- Colorado State University Extension, Home Sprinkler Systems: Preparing Your Sprinkler System for Winter (Fact Sheet 4.719; published October 2014, reviewed August 2025), retrieved .
- Colorado State University Extension, Home Sprinkler Systems: Backflow Prevention Devices (published April 2003, reviewed August 2025), retrieved .
- Medford Water (Oregon), Winterizing, retrieved .
- Irrigation Association of New York, Winterization Basics by Rod Waller, Rain Bird Corporation (February 10, 2007), retrieved .
- Rain Bird Sales, Inc. Turf Products, Technical Newsletter Special Issue, Protect Your Irrigation System From Winter Damage (Fall 2000), PDF read as text, retrieved .
Expert review
Written by the HyreYard Research Desk. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Method descriptions, backflow guidance and controller notes come from Colorado State Extension fact sheets, Medford Water, an IANY article by a Rain Bird author and a 2000 Rain Bird technical newsletter read as text from a PDF.
Air pressure and volume figures are given only as each source prints them, side by side, with their different scopes.
No step-by-step blowout is given, and the page tells readers to use a licensed irrigation contractor. Held for a qualified reviewer under G-REV; none is named. No prices are given.
Suggest a correction. We fix errors and say what changed.