How to Winterize a Sprinkler System

To winterize a sprinkler system, shut off the water supply, switch the controller to rain mode, and get every drop of water out of the pipes before the first hard freeze — either by blowing the lines out with compressed air, draining them manually at the lowest points, or letting automatic drain valves empty them. Do it in October in most northern states, as soon as nighttime lows start dipping into the 30s. If you use air, keep pressure at 50 PSI or lower and never exceed 80 PSI, and always connect the compressor downstream of the backflow preventer — never blow air through the backflow device itself.

That is the whole job in one paragraph. Skip it, and water trapped in the pipes freezes, expands, and cracks lines, valves, and backflow preventers — repairs that routinely cost $500 to $2,000 or more in spring. Below is the full process: when to do it, the three draining methods compared, the exact blow-out steps, backflow care, the mistakes that cause most freeze damage, and what it costs to hire it out instead.

What Happens If You Don’t Winterize Your Sprinkler System?

Water expands by roughly 9% when it freezes. Inside a rigid PVC pipe, a valve body, or a brass backflow preventer, that expansion has nowhere to go — so something cracks. The damage often stays hidden until you start the system in spring and find a geyser in the lawn or a flooded valve box. Typical repair costs:

Freeze Damage	Typical Repair Cost
Burst underground pipe (per break)	$400 – $1,200
Cracked backflow preventer (replacement)	$500 – $1,800
Broken zone valve (each)	$150 – $450
Damaged sprinkler heads (each)	$20 – $75

Compare that with winterizing: about an hour of your time, or $75–$150 for a professional visit. There is no cheaper insurance for an irrigation system.

When Should You Winterize a Sprinkler System?

The rule is simple: finish before the first hard freeze (a freeze at or below 28°F that lasts several hours). Even a few nights dipping below 32°F can crack exposed pipes and backflow preventers, so don’t wait for a hard freeze to be forecast. Practical timing by region:

Region / USDA Zones	Winterize By
Northern US — zones 3–4 (MN, ND, northern New England)	Early to mid-October
Midwest & Northeast — zones 5–6 (Chicago, Denver, New York)	Mid to late October
Transition zone — zones 7–8 (Nashville, Dallas, Pacific NW)	Late October to mid-November
Mild South — zone 9+ (Houston, Phoenix)	Only before rare hard freezes; drain above-ground parts

A good trigger: when nighttime lows are consistently in the 30s, book the job within the next week or two. Fall is also when your lawn’s needs change in other ways — taper off your watering schedule as growth slows, and our guide to protecting your lawn during winter covers the rest of the pre-winter checklist.

What You Need to Winterize a Sprinkler System

• Air compressor (blow-out method) — volume matters more than pressure. Small 1–3 HP garage compressors usually can’t move enough air. You want a unit rated around 10 CFM minimum for small systems; professionals use 80–100 CFM tow-behind units. A quick estimate: take your largest zone’s flow in GPM and divide by 7.5 to get the CFM you need.
• Blow-out adapter / fitting — to connect the compressor hose to the system’s test cock, quick-coupler, or blow-out port (about $10–$20).
• Pressure regulator — if your compressor doesn’t have one built in.
• Safety glasses — debris can eject from sprinkler heads under pressure.
• Insulation or a backflow cover — foam pipe insulation, an insulated pouch, or a fake-rock cover ($10–$40).
• Flathead screwdriver — for backflow test cocks and manual drain valves.

Before You Drain Anything: Shut-Off Order

Every method starts the same way:

1. Shut off the water. Close the irrigation system’s main shut-off valve (often in the basement or a valve box near the meter). Some systems have a dedicated stop-and-waste valve — that also drains the supply line.
2. Set the controller to “rain mode” (sometimes labelled “off” or “suspend”). Rain mode stops watering but keeps your programmed schedules in memory for spring. Don’t just unplug it — many controllers lose programming, and some need the clock battery anyway.
3. Note your backflow preventer type — pressure vacuum breaker (PVB, most common on homes), reduced pressure zone (RPZ), or double-check valve. The draining steps below apply to all three, with a small difference noted in the backflow section.

Method 1: The Blow-Out Method (Most Thorough)

Blowing out with compressed air is the standard method in cold climates and the one professionals use. Done right, it clears water from pipes, valves, and heads that gravity draining can’t reach. Done wrong — too much pressure, or air forced through the backflow preventer — it causes the very damage you’re trying to prevent. Follow the order exactly:

1. Connect the compressor downstream of the backflow preventer. Attach at a test cock or blow-out port on the irrigation side of the backflow device. Never blow air through the backflow preventer — the heat from compressed air deforms its internal seals (manufacturer Hunter is explicit about this).
2. Close the backflow isolation valves so air and water are pushed toward the zones, not back toward the house.
3. Set the regulator low to start — 30–40 PSI — then raise only as needed. Maximum 50 PSI on polyethylene pipe and 80 PSI on rigid PVC. If you don’t know your pipe type, stay at or under 50 PSI: that is within every major manufacturer’s limit.
4. Start with the zone farthest from the compressor / at the highest elevation. Open it from the controller (set that zone to run manually) or at the valve.
5. Blow each zone for about 2 minutes per pass. You’ll see full spray, then sputtering, then a fine mist. Move to the next zone rather than running air through a dry one — prolonged air friction overheats and damages gear-drive rotor heads.
6. Cycle through all zones 2–3 times until only mist comes out of the heads. Some water resettling between passes is normal.
7. Finish at the mainline: briefly blow the mainline itself if your setup allows, then disconnect the compressor.
8. Drain the backflow preventer separately (next section), and open any manual low-point drains for a final release.

Safety: wear eye protection, never stand directly over a sprinkler head or valve while a zone is pressurised, and never exceed 80 PSI under any circumstances.

Method 2: Manual Drain Method

If your system’s pipes were installed with manual drain valves at the low points, gravity can do most of the work — no compressor needed:

1. Shut off the water and set the controller to rain mode (as above).
2. Locate the manual drain valves — usually at the lowest point of the mainline and each zone line, often in valve boxes.
3. Open them one at a time and let the water run out completely. This can take a while on large systems.
4. At each electric zone valve, loosen the bleed screw or turn the solenoid a quarter-turn to let trapped water escape past the valve, then re-tighten.
5. Once flow stops everywhere, close the drain valves.

Limitation: manual draining alone leaves small pockets of water in valves and low spots in flexible poly pipe. In genuinely cold climates (zones 6 and colder), most installers still recommend a blow-out to finish the job.

Method 3: Automatic Drain Method

Some systems have automatic drain valves that open whenever mainline pressure drops. If yours does:

1. Shut off the water supply and set the controller to rain mode.
2. Run each zone briefly from the controller to release pressure and trigger the drains.
3. Walk the yard and check that water has actually drained at the low-point valves — auto-drains clog with age and sediment, and a stuck one leaves a full pipe.
4. Still drain the backflow preventer by hand (below).

Even with auto-drains, many northern installers add a light blow-out in very cold winters. Auto-drain valves are the most commonly skipped check — verify them, don’t trust them.

How to Winterize a Sprinkler System Without a Compressor

No compressor and no manual drains? You still have options:

• Gravity drain through the backflow and low points — open every low valve, test cock, and head at elevation lows; on sloped systems this removes most water.
• Wet/dry shop vacuum — at an open drain or removed head, a strong shop vac can pull residual water from short runs. Less effective than air, better than nothing.
• Hire it out once — a pro blow-out costs $75–$150 (below) and includes the compressor you’d otherwise rent for $30–$60 a day plus fittings. For many homeowners this is the rational choice.

What not to do: never add automotive antifreeze to an irrigation system — it’s toxic to soil and groundwater. (Non-toxic propylene-glycol antifreeze exists for plumbing traps, but it has no place in sprinkler lines that water a lawn.)

Don’t Forget the Backflow Preventer

The backflow preventer is the most expensive freeze casualty because it’s brass, above ground, and full of small water passages. After the lines are drained:

1. Open the small test cocks with a flathead screwdriver and let the device drain.
2. Turn the ball-valve handles to a 45-degree angle — halfway between open and closed. A fully open or fully closed ball valve traps a pocket of water inside the ball, which is what cracks the brass body. The 45° position lets that water escape.
3. For an RPZ device, also open the relief port briefly to drain its chamber. For a PVB, the same 45° rule applies to its shut-off valves.
4. Insulate it: wrap with foam insulation and cover with an insulated pouch or backflow cover. In very cold climates (zone 5 and colder), many plumbers remove the device entirely and store it indoors — if you do, cap the open pipes.

Rain Sensors and Smart Controllers (The Step Most Guides Skip)

If your system has a rain or freeze sensor, winterize it too: open the sensor’s cap and let any collected water drain, and on models with absorbent discs or a battery, remove them for the season so they don’t freeze and split the housing. For smart (Wi-Fi) controllers, rain mode usually works the same way — but also check the app still has your zones and schedules saved before you disconnect anything, and take a photo of your valve box layout. Future-you, standing in a muddy yard in April, will say thanks.

Common Winterizing Mistakes

• Too much air pressure. Over 80 PSI can shred pipe fittings and seals. Volume (CFM) clears lines — pressure just needs to be moderate.
• Blowing air through the backflow preventer. Always connect downstream of it. Air heat ruins its seals.
• Forgetting the main shut-off. If the supply valve leaks even slightly, lines quietly refill all winter and freeze anyway.
• Leaving the controller in “auto.” A warm snap or a power glitch can start a cycle you won’t notice. Rain mode, every time.
• Skipping the low-point drains. Blown-out zones still leave water in the mainline’s low spots.
• Blow-out with a tiny compressor, once, too fast. Underpowered units leave water behind; the mist test (2–3 passes) is the proof, not the clock.
• Using automotive antifreeze. Toxic — never in irrigation lines.

Cost: DIY vs. Hiring a Pro

Option	Typical Cost
Professional winterization visit	$75 – $150 (national average ≈ $91)
DIY — compressor rental (1 day)	$30 – $60
DIY — adapter, insulation, cover	$10 – $40
DIY — if you own a suitable compressor	Under $20 in fittings

Pros also spot weak valves and leaking shut-offs you might miss. But if you own or can rent a compressor with enough CFM, the DIY route is straightforward and saves the annual fee — the same seasonal mindset that has you checking your snowblower before winter applies here: an hour in October prevents a repair bill in April.

Already Froze? What to Do Now

If a freeze caught you before winterizing, don’t force the system on. Leave the supply off, let everything thaw naturally, and winterize late rather than never — draining now still protects against the next, harder freeze. In spring, start up slowly: pressurize one zone at a time and walk the line watching for geysers, soggy spots, or a meter that spins with everything off — all signs of a cracked pipe or valve to repair before the season starts.

Frequently Asked Questions

What PSI should I use to blow out my sprinkler system?

Stay at or under 50 PSI — safe for both pipe types. The hard maximums are 50 PSI for polyethylene pipe and 80 PSI for rigid PVC. If you’re unsure which pipe you have, 50 PSI is within every manufacturer’s limit. Volume (CFM) matters more than pressure for actually clearing the lines.

How long should I blow out each zone?

About 2 minutes per pass, cycling through all zones 2–3 times until only a fine mist exits the heads. Stop once a zone runs dry — running air through dry lines overheats gear-drive rotors.

Can I blow out sprinklers with a small home compressor?

Usually not well. Most 1–3 HP garage compressors lack the air volume (CFM). Estimate your need: largest zone’s GPM ÷ 7.5 = required CFM. Renting a high-CFM unit for a day ($30–$60) is the common fix.

Do all sprinkler systems need to be winterized?

Any system in a climate with frost below the pipe depth, or with above-ground parts (backflow preventers especially), needs it. In frost-free climates, no. In mild zones (9+), draining and insulating the above-ground backflow before a rare hard freeze is usually enough.

When is it too late to winterize?

After the first hard freeze, some damage may already exist — but winterizing late still prevents worse damage from later freezes. Do it as soon as you can; in spring, inspect carefully at start-up.

Should I remove the backflow preventer for winter?

Not usually. Draining it, setting handles at 45°, and insulating is sufficient in most climates. In very cold regions (zone 5 and colder), removal and indoor storage is common extra insurance.

The Bottom Line

Winterizing a sprinkler system is one hour of methodical work: shut the water off, set the controller to rain mode, drain or blow out every line (50 PSI max if you’re unsure of pipe type, connected after the backflow), drain and insulate the backflow preventer with handles at 45°, and open the low-point drains. Do it before the first hard freeze — in most of the northern US, that means October. The alternative is a $500–$2,000 spring surprise, and no lawn needs that.