How to Winterize a Sprinkler System: When to Do It, Blow-Out vs. Drain, and the Pressure Limits That Save Your Pipes

The whole job of learning how to winterize a sprinkler system comes down to one number: water grows about 9% in volume when it freezes (U.S. Geological Survey). Inside a closed pipe that expansion has nowhere to go, and an engineering study that froze water in sealed PVC and CPVC lines measured pressures of 1,800 to 2,575 psi before failure — more than 30 times normal household pressure — with the break often appearing far from the spot that froze (Cruz, Davis, Gramann & Rios, The Madison Group). The irrigation lines under a lawn, the valves in the manifold box, and above all the backflow preventer standing in the open air are exactly that kind of closed pipe once the water is shut off. Getting the water out, or giving it room to expand, is the entire task.

This guide covers what freezing does inside irrigation pipe, where water hides in a residential system, the pressure and air-volume numbers for a blow-out, when to do it in your part of the country (with NOAA first-freeze dates for 25 cities), the mistakes that cause spring repair bills, and the exact steps for the controller and soil moisture sensors. A professional blow-out costs a national average of $93 in 2026 (Angi); replacing one cracked valve runs $65 to $290 and one sprinkler head $130 to $275 installed (HomeGuide). The arithmetic favors doing it, and doing it right.

Part 1: The physics — what freezing does inside a pipe

Ice floats because it is less dense than the water it formed from: on freezing, water's density drops by about 9%, which is the same as saying its volume grows by about 9% (USGS Water Science School). Colorado State University Extension puts it in plumbing terms: "11 cubic feet of water will form approximately 12 cubic feet of ice," an expansion "sufficient to cause pipes and fittings to burst, valves to crack, and sprinkler and pump cases to split open" (CSU Fact Sheet 4.719).

The part most homeowners get wrong is where the damage happens. A pipe rarely bursts at the point that freezes first. Field research by the Building Research Council at the University of Illinois, summarized in the Institute for Business & Home Safety's pipe-freeze guidance, found that an ice plug forms, then "continued freezing and expansion inside the pipe causes water pressure to increase downstream — between the ice blockage and a closed faucet at the end. It's this increase in water pressure that leads to pipe failure" (IBHS, Freezing and Bursting Pipes). The Madison Group's laboratory work on PVC and CPVC reached the same conclusion from the other direction: "bursting of water pipes does not occur directly from the physical pressure applied by the growing ice but by the excessive water pressure generated from ice formation," and "failure often occurs at a remote section of pipe through an indirect mechanism" (Cruz et al.). In a sprinkler system, the "closed faucet" is any shut valve: the main shutoff, a closed ball valve on the backflow preventer, a zone valve that is holding back a column of water. That is why every winterization guide ends with valves left open or half-open rather than closed.

Two more findings from the Illinois work shape the schedule. For uninsulated pipe in an unheated space, "the onset of freezing occurred when the outside temperature fell to 20 degrees Fahrenheit or below," which is why IBHS sets a "temperature alert threshold" of 20°F, and wind chill "can play a major role in accelerating ice blockage" because moving air strips heat from exposed pipe far faster than still air (IBHS). A backflow preventer bolted to the side of a house, with its thin brass body and rubber seals, gets both the cold and the wind. Oklahoma State University Extension names it directly: the components that fail are "back-flow prevention devices and pipes exposed to freezing temperatures," while most buried lines sit below the worst of it (OSU Extension). Soil also freezes from the top down and lags the air by weeks, so a buried lateral survives the first frosty nights that would crack an exposed valve. Buried is not the same as safe, though: by midwinter in a cold climate the frost line reaches well past the shallow depth at which most residential laterals are buried.

Part 2: The anatomy — where water hides in a sprinkler system

A residential system has a predictable set of places that hold water after the supply is shut off, and each one is handled differently. Working from the house outward:

The main shutoff. Usually a stop-and-waste valve or ball valve in the basement, crawl space, or a buried box near the meter. Closing it is step one in every extension and manufacturer procedure, because it is the only thing that stops the system refilling from the house supply (Utah State University Extension). A stop-and-waste valve has a small drain port on the downstream side so the short run of pipe between the valve and the backflow preventer can empty.

The backflow preventer. A pressure vacuum breaker (PVB) or reduced-pressure (RP) assembly mounted above grade, with a ball valve on each side and small test cocks on the body. It is pressurized all season, exposed to the wind, and full of rubber seals. Hunter's winterization manual is blunt: "Do not blow the system out through a backflow or pump." CSU adds the reason: PVB and RP devices "should never be blown out with compressed air. The rubber seals inside can easily melt from the heat of the air" (CSU 4.719). It is drained through its own test cocks, and its ball valves are left at 45°, as explained in Part 3.

The mainline and the blow-out port. From the backflow preventer a mainline runs, pressurized all season, to the valve manifold. The compressor connects to a fitting on this line, and Hunter specifies where: it has you "attach the air compressor hose to the fitting" located "after the backflow device," so air flows downstream toward the zones and never through the device (Hunter Industries). If your system has no port, an irrigation supplier sells a hose-bib or quick-connect fitting that installs in minutes.

The valve manifold. Each zone's solenoid valve has a body that holds water whether the valve is open or shut. The University of Georgia's drip winterization circular states the rule for every kind of irrigation valve: "Open all valves, as closed gate and ball valves trap water and can crack/break when repeated freeze/thaw cycles occur" (UGA Circular 1094). Rain Bird's homeowner guide has diaphragm valves left with the "solenoid in open position for winter" and manual valves "in open position" (Rain Bird Homeowner's Guide to Winterization).

The laterals and heads. Lateral lines downstream of each valve run to the sprinkler heads and are either white rigid PVC or black polyethylene, which matters for the pressure limit. They have low spots that gravity cannot clear, and heads with built-in check valves hold water in the riser unless the head is pulled up or blown through. Automatic drain valves at low points open when line pressure falls below about 10 psi (Hunter; UGA says 9 to 10 psi), but CSU does not recommend relying on drains alone "since sub-surface pipes have a tendency to shift with time and there is no way to visually inspect lines once draining is complete"; compressed air is "the only positive way to be sure enough water has been expelled from the system" (CSU 4.719).

Drip zones and hose gear. A drip zone adds a filter, a pressure regulator, and emitter tubing; UGA's checklist drains the filter and disconnects "any pipe or component in which water cannot be drained by gravity" (UGA C1094). Battery hose timers, hose-end flow meters, and hoses come off the spigot entirely: Soildrops' hose timers carry the instruction to "remove the timer, drain it completely, and store it indoors" before freezing weather, and freeze damage is excluded from the warranty on timers and the FLM-001 flow meter alike (Soildrops hose timer). Our drip irrigation design guide shows how those components are laid out.

Part 3: The practical math — pressure, air volume, and time per zone

Three numbers decide whether a blow-out protects the system or damages it: the air pressure at the pipe, the air volume the compressor can deliver, and how long each zone runs.

Pressure. Hunter's limits are 80 psi for rigid PVC and 50 psi for polyethylene, and "should NEVER exceed 80 PSI" for any system (Hunter Industries). CSU gives the same ceilings and an ideal range of 40 to 80 psi (CSU 4.719). Rain Bird's homeowner guide is simpler and stricter: "Air pressure must not exceed 50 pounds per square inch" (Rain Bird). If you do not know which pipe is under your lawn, use 50 psi. A typical 6-gallon portable "pancake" compressor stores air at up to 165 psi (DeWalt DWFP55126 manual), so the regulator between the tank and the hose is not optional; set it before the hose is connected, with a gauge you can read while the zone is running.

Air volume. Compressor output is rated in cubic feet per minute (CFM), and the gap between homeowner and contractor equipment is large. Rain Bird's homeowner guide calls for 10 to 25 CFM; Hunter specifies 80 to 100 CFM for mainlines up to 2 inches; the truck-mounted units professionals use run 185 CFM (Rain Bird, 2025). The 6-gallon pancake compressor in most garages is rated at 2.6 CFM at 90 psi (DeWalt DWFP55126 manual). CSU gives the rule of thumb for what a zone actually needs: "Divide GPM by 7.5 to determine the cubic feet per minute (CFM) needed," because a cubic foot holds 7.48 gallons, so a 12-gallon-per-minute zone moves 1.6 cubic feet of water a minute and needs at least that much air to push it out at the speed it came in.

Here is why the small compressor still works, slowly. A 6-gallon tank is 0.8 cubic feet; pumped to 165 psi it holds roughly 10 cubic feet of free air, and by the time the tank has fallen to 50 psi it has released about 6 cubic feet of free air, which at 50 psi in the pipe occupies roughly 1.4 cubic feet. Two hundred feet of 1-inch lateral holds about 9 gallons of water, or 1.2 cubic feet. So one tank-full clears roughly one zone's worth of water, after which the compressor needs a couple of minutes to recover (these are our round numbers from the tank size and Boyle's law, not a manufacturer rating). What the small unit cannot do is keep air moving fast enough to scour water out of low spots in one pass, which is why both manufacturers prescribe repeat cycles rather than one long blast.

Time and sequence. Rain Bird: "Do not blow any circuit more than 2 minutes at a time," starting with "the circuit that is furthest from the air connection," repeating "two or more times" until "nothing more than a fine mist appears" (Rain Bird). Hunter: run each zone "until no water can be seen exiting the heads, this should take approximately two minutes or more," farthest zone first, and "it is better to use two or three short cycles per station/zone than to have one long cycle" (Hunter). CSU: "Each zone/station should be blown out twice." The two-minute cap is a heat limit. Compressed air warms as it flows, and a gear-drive rotor spinning dry on hot air can, in Rain Bird's words, "melt the rotor head together."

The backflow preventer, specifically. After the zones are clear, drain the device through its test cocks (the small screwdriver-slot valves on the body), then follow Hunter's sequence: "open and close the isolation valves on the backflow device numerous times" to shake water out of the ball valve cavities and "leave the isolation valves open at a 45° angle" with the test cocks open (Hunter). Rain Bird explains the 45°: "Ball type shutoff valves should be left at a 45 degree angle to prevent water from entering the seal." A fully closed ball valve traps a pocket of water inside the ball; a fully open one lets the pipe drain into it. Half-open is the only position that does neither. Then put an insulated cover on it. If a frost night arrives before you have winterized, the cover and a closed main shutoff buy time; they are not a substitute for draining it.

Before any of this, two checks. Bleed the pressure first: with the main shutoff closed, run one zone from the controller for a minute so the mainline is at zero before the compressor is connected — the reason Rain Bird has you open a valve before the compressor starts, and the reason the controller stays plugged in through the blow-out. And if a zone leaked or never held pressure this season, fix it first; air escaping through a split fitting will not clear the heads downstream of it. If you ran a catch-cup test or a pressure test this year, you already know each zone's flow rate for CSU's CFM formula.

Part 4: The schedule — when to winterize, by city

The National Weather Service defines a hard freeze as "surface air temperature reaches 28°F or lower for an extended period of time" (NWS glossary). That is the deadline Soildrops' own support guidance uses — winterize "before your area's first hard freeze" — and it is the event that cracks an unprotected backflow preventer (Soildrops support). The question is when that happens where you live, and NOAA answers it. The 1991–2020 U.S. Climate Normals include, for every major station, the date by which there is a 50% chance the first 32°F night has occurred, the same for 28°F, and the date by which it has happened in one year out of ten (NOAA NCEI Climate Normals, data types ANN-TMIN-PRBFST-T32FP50, T28FP50 and T32FP10). Twenty-five airport stations, pulled from NCEI on October 4, 2026:

How to use the table. Your lawn still wants water until the soil cools, and a dry lawn going into winter is more prone to desiccation injury, so the sequence in our fall lawn watering guide applies: taper through October, give one last deep watering if the soil is dry, then winterize. Aim to have the blow-out done in the week of your median first-32°F date, treat the median 28°F date as the hard deadline, and put the insulated cover on the backflow preventer by the one-in-ten date, because that is the night that catches people. In Denver that means a cover by late September and a blow-out in the first half of October; in Atlanta or Seattle it means late November, and in Sacramento many systems are simply drained and covered rather than blown out. If you hire the work out, book early: Soildrops' support guidance notes that blow-out providers book up weeks ahead, and HomeGuide's cost survey frames the season as "between August and November before the first big freeze of the year" (HomeGuide).

Warm-climate exception. In the Gulf South, coastal California, and the low desert, hard freezes are rare and short, and many homeowners never blow out. The risk is still the above-ground assembly on a cold snap that lasts a few hours. The minimum program there is a closed main shutoff, a drained and covered backflow preventer, hose timers and meters brought in, and the controller paused on freeze nights so heads do not run and ice the sidewalk.

Spring is the reverse of this list, and it has its own date: reopen the main slowly, inspect the backflow preventer for cracks before it takes full pressure, run each zone briefly, and only then hand the schedule back to the controller. Our spring lawn watering guide covers when the lawn actually needs the system back on, which is later than most people restart it.

Part 5: Common sprinkler winterization mistakes

1. Blowing air through the backflow preventer. The compressor gets connected at the hose bib upstream of the device because that fitting is convenient. Hot air then passes over the rubber check seals and poppet, and CSU warns they "can easily melt from the heat of the air." Connect downstream of the device, as Hunter specifies, and drain the device through its own test cocks.
2. Running an unregulated compressor. A pancake tank at 165 psi connected straight to a polyethylene lateral rated for 50 psi of air is a split fitting waiting to happen, and the break will be somewhere underground. Set the regulator to 50 psi (80 for PVC you can identify), confirm it on the gauge with a zone open, and never raise it to "speed things up."
3. One long blast per zone. Past two minutes the air is doing more heating than clearing; rotors spin dry, and gear drives can fuse. Two or three short cycles, farthest zone first, move more water than one long run because each pause lets water in low spots flow back to where the next burst can catch it.
4. Trusting the drain valves. Automatic drains open below about 10 psi and manual drains sit where the installer put them a decade ago. Pipes settle, low spots migrate, and you cannot see inside. CSU's position is that compressed air is "the only positive way" to know the lines are empty.
5. Closing the ball valves tight. It feels like the safe choice. It traps water inside the ball, and the IBHS research shows the burst happens where pressure builds against a closed valve. Forty-five degrees, test cocks open.
6. Leaving the zone valves closed. Same mechanism, one step downstream. Rain Bird leaves solenoids in the open position for winter; UGA's rule is "open all valves."
7. Waiting for the average. The median first freeze is the date by which half of years have already frozen. One year in ten, Chicago freezes by October 3, Boston by October 27. The backflow cover should be on before that date even if the blow-out is still on the calendar.
8. Forgetting the small gear. Hose timers, flow meters, drip filters and pressure regulators hold a few ounces of water in bodies designed for 100-plus psi of water, not ice. Soildrops' hose timers and flow meter exclude freeze damage from warranty coverage, as every manufacturer does, because it is avoidable. Drain them and bring them inside.
9. Skipping eye protection and standing over the heads. Hunter prints it in capitals: wear ANSI-approved safety glasses, and "do not stand over any irrigation components" while the system is pressurized. A head that pops its cap under 50 psi of air leaves at speed. Keep pets inside too; CSU notes the whistling heads upset them.

Part 6: Sensors and the controller — the Soildrops winter procedure

A sensor-based system has two extra items on the list, and Soildrops publishes the exact procedure in its support center (Winterizing Your Soildrops System). The order matters.

Keep the controller plugged in for the blow-out. You or the technician will open each zone from the app's Quick Run while the air is on, which is the clean way to bleed pressure before connecting the compressor and to cycle zones farthest-to-nearest without walking to the manifold. The Soildrops 8-zone controller has no master valve or pump-start terminal, so there is nothing extra to disconnect on a city-water system. If you want everything stopped while you work, Settings → Zones → Pause All Schedules "pauses everything until you turn it back on — nothing is deleted" (Soildrops support).

Pull the soil moisture sensors before the ground freezes. The Soildrops sensor is a push-in probe with a 6-inch measurement depth, and frozen soil can grip and damage a probe that is pulled later. Soildrops' instruction is to "pull your soil moisture sensors before the ground freezes," extract them gently and vertically, wipe them clean, and store them indoors; the pairing to each zone persists through the winter and the CR2477 battery stays installed. Pull them in the same week as the blow-out — the lawn has stopped taking water by then, so the readings are no longer driving anything. In spring they go back into moist soil (water the spot first if it is dry) in the same representative location, which our sensor placement guide explains how to choose.

Then unplug the controller. This is where Soildrops differs from the Hunter and CSU advice to keep a conventional controller powered all winter, and the difference is architectural. Conventional controllers store their programs in the box and, in CSU's recommendation, run a dry minimum cycle weekly to keep solenoid plungers from sticking. Soildrops stores "every zone, schedule, and sensor pairing" in your account, not the box, so the instruction is simply: "just unplug it. It draws zero power all winter." Do not factory-reset it; the app will show it offline, which is normal, and offline-alert emails can be paused in the notification settings. In spring, plug it in, "all four LEDs light up and it rejoins your Wi-Fi automatically," reinstall the sensors, run a brief Quick Run on each zone to confirm the heads survived, and confirm the schedules. If you prefer to keep winter soil-moisture readings in the app — useful in dry-winter climates where a dormant lawn occasionally needs water above 40°F — leave the controller plugged in with all schedules paused and leave the sensors in only where the ground does not freeze; everywhere else, follow the pull-and-store instruction.

Done this way, the system comes back in April with no cracked valve bodies and a controller that resumes Autopilot, Smart, or Manual mode where it left off. For anyone still on a clock timer, the shutdown is the natural moment to switch: a controller-and-sensor starter kit goes onto the same 24 VAC valve wiring in under half an hour, and the spring restart is the first schedule it writes (our smart sprinkler controller guide covers what to look for).

Frequently asked questions

When should I winterize my sprinkler system?

After the lawn's last deep watering and before the first 28°F hard freeze. Use the NOAA table above: book the blow-out for the week of your city's median first-32°F date and treat the median 28°F date as the deadline. Put an insulated cover on the backflow preventer earlier, by the one-in-ten early-freeze date, because the above-ground assembly is the first thing to crack.

Can I blow out my sprinklers with a pancake compressor?

Yes, slowly and in short cycles, if you regulate the pressure. A 6-gallon unit rated around 2.6 CFM clears roughly one zone per tank-full and then needs a few minutes to recover, against the 10 to 25 CFM Rain Bird suggests for homeowners. Set the regulator to 50 psi (80 for confirmed PVC), run each zone no more than two minutes at a time, farthest zone first, and repeat each zone until only mist comes out. If the system has long runs, many low spots, or you cannot find a port downstream of the backflow preventer, the $56 to $137 a professional charges is cheap insurance.

What psi should I use to blow out sprinkler lines?

No more than 50 psi for polyethylene (black) pipe and 80 psi for rigid PVC, per Hunter and Colorado State University Extension; Rain Bird's homeowner guide caps everything at 50 psi. When in doubt, 50. Pressure is what protects the pipe; air volume is what moves the water.

Do I need a blow-out if my system has drain valves?

In a climate with real winters, yes. Automatic drains open below about 10 psi and manual drains work only where the pipe still slopes toward them. CSU does not recommend drains as the sole method because buried pipe shifts over time and cannot be inspected; compressed air is the only way to confirm the lines are empty. In mild climates with brief light freezes, draining plus a covered backflow preventer is a reasonable minimum.

How do I winterize drip lines, hose timers, and a soil moisture sensor?

Drip: open the valves and the end caps, drain the filter and pressure regulator, and disconnect anything that cannot drain by gravity, following the UGA checklist. Hose timers and hose-end flow meters come off the spigot, get drained, and go indoors; freeze damage to them is excluded from warranties across the industry. Soildrops soil moisture sensors are pulled before the ground freezes, cleaned, and stored inside; the zone pairing and battery stay as they are.

What happens if I skip winterizing?

In a hard-freeze climate the backflow preventer usually goes first, then valve bodies and low-lying laterals, and the failures appear as geysers or soggy patches in April. HomeGuide's 2026 figures put one valve replacement at $65 to $290 and one head at $130 to $275 installed; a blow-out averages $93. Ice in a closed line generates pressures in the thousands of psi, and the burst happens wherever the pipe is weakest, not where it froze.

The bottom line

Winterizing a sprinkler system is a sequence, not a trick: shut the water off, bleed the pressure, push the water out with regulated air at 50 or 80 psi for no more than two minutes a cycle, drain the backflow preventer through its own test cocks and leave its valves at 45°, open the zone valves, bring the small gear indoors, pull the sensors, unplug the controller. Done in the week of your median first freeze, with the backflow covered before the one-in-ten early date, it costs an afternoon or about $93, and it is the difference between a system that comes back with one Quick Run in April and one that comes back with a shovel.

The audit you can do today: find your main shutoff and your backflow preventer and confirm you can close one and reach the test cocks on the other. Look for a blow-out port downstream of the backflow; if there is none, buy the fitting now. Read the CFM-at-90-psi rating on your compressor's label and decide whether you are doing this yourself or booking a professional. Then look up your city in the table, write the median 32°F and 28°F dates on the calendar, and put the insulated cover within reach by the earlier one.

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About this article. Researched and written by the Soildrops content team, drawing on Colorado State University Extension Fact Sheet 4.719, Utah State University Extension, Oklahoma State University Extension, University of Georgia Cooperative Extension Circular 1094, the winterization guides published by Hunter Industries and Rain Bird, NOAA National Centers for Environmental Information 1991–2020 climate normals, the National Weather Service, the U.S. Geological Survey, the Institute for Business & Home Safety's summary of University of Illinois Building Research Council field tests, an engineering study of freezing in PVC and CPVC pipe systems by The Madison Group, 2026 cost surveys from Angi and HomeGuide, and Soildrops product and support documentation. All scientific claims are linked to original sources. Last updated October 2026.