Identify the system, protect the backflow device, and know when compressed-air winterization belongs with an irrigation professional.
Winterize an in-ground sprinkler system after its last watering and before freezing weather by shutting off the irrigation supply, protecting exposed parts, setting the controller correctly, and removing water by the method the system was designed to use. Do not assume that closing the valve or opening one drain empties every line. If compressed air is required and you cannot identify the pipe, backflow device, blowout connection, pressure limit, and needed air volume, hire an irrigation professional.
This is one fall job where “more pressure” can make the outcome worse. A careful homeowner can map the system, shut down the supply, document the equipment, and prepare the site. The blowout itself has projectile, noise, pressure, and equipment-damage risks.
First decide whether your system needs winterizing
Buried irrigation in a climate without soil-freezing weather may have a different shutdown procedure from a system in a hard-freeze region. Start with the installer record, controller manual, valve and backflow labels, and local water-district or extension guidance. The system manufacturer’s instructions control when they are more restrictive.
Colorado State University Extension explains why the job matters: water expands by about one-eleventh when it freezes, enough to split pipe, valves, sprinkler bodies, pumps, and fittings. Exposed backflow assemblies and risers are vulnerable first. Buried lines become vulnerable as freezing reaches their depth.
Do not winterize simply because the calendar says October. Stop regular watering when plants and local rules allow, then schedule the shutdown before the first hard freeze expected to threaten the equipment. In warmer regions, the correct plan may be draining exposed parts and insulating them, not copying a northern blowout procedure.
Identify the system before touching a valve
Walk the property while the system still operates normally. Number every zone at the controller and mark which heads or drip lines run. Photograph the irrigation shutoff, backflow preventer, pump, filter, pressure regulator, drain points, blowout fitting, valve boxes, and controller wiring. Save the photos with the seasonal home-care calendar.
Then answer these questions:
- Is the irrigation supply separate from the home’s main water shutoff?
- Is there a stop-and-waste valve, manual drain, automatic drain, or dedicated downstream blowout fitting?
- Does the system use rigid PVC, flexible black polyethylene, drip tubing, or a mix?
- What type of backflow prevention device is installed?
- Does the controller operate a pump or master valve?
- What gallons-per-minute flow and pressure were designed for the largest zone?
Unknown hardware is a stop sign, not an invitation to experiment. A valve in a deep box may require a key and can break if forced. A connection that resembles a convenient air port may be on the wrong side of the backflow device.
Choose the drainage method the installation supports
| Method | When it may fit | Main limitation |
|---|---|---|
| Manual drain | Installed low-point drains and pipe laid to drain by gravity | Settled pipe, low spots, valves, and closed sections may retain water |
| Automatic drain | Purpose-built valves that open as water pressure falls | The homeowner cannot see whether every valve opened or every low point cleared |
| Compressed-air blowout | Systems designed with a proper downstream connection and known component limits | Wrong pressure, low air volume, heat, or a closed path can damage equipment or injure people |
| Professional winterization | Mixed materials, unknown layout, pumps, RP devices, no safe fitting, or limited homeowner equipment | Costs more than a basic drain, but transfers a high-risk step to trained help |
Rain Bird describes all three drainage methods but recommends contacting a local irrigation specialist because of the safety risks. Colorado State University Extension is stricter for systems in freezing climates: gravity drains can leave water behind, and electric valves retain water above the diaphragm, so pressurized air is the positive removal method.
Safe homeowner preparation
- Finish the last needed watering and inspect every zone for existing leaks, broken heads, or poor flow.
- Save the controller schedule, zone map, and equipment labels. Note any pump or master-valve circuit.
- Close the dedicated irrigation supply slowly. Do not force a buried or corroded valve.
- Relieve water pressure only through the installed method and according to the system instructions.
- Disconnect and drain hoses, hose-end timers, removable filters, and other accessories whose manuals call for indoor storage.
- Keep people and pets away from heads, valve boxes, fittings, and the compressor work area.
- Set the controller to its documented Off, Rain, or Winter mode. Handle pump controls exactly as their manual directs.
Do not add automotive or RV antifreeze to lawn irrigation. The system connects to soil and may connect to potable water through a protected supply. Use only an approved procedure for the exact installation.
Why a blowout is often professional work
Compressed air stores energy. A loose fitting or sprinkler part can become a projectile, and debris can leave a head at eye level. Wear eye protection, but do not treat glasses as permission to guess. Keep clear of every discharge point while the system is pressurized.
Pressure is only half of the sizing problem. Colorado State University Extension says to divide the largest zone’s gallons per minute by 7.5 to estimate the required cubic feet per minute of air. Its guidance lists ideal pressures of 40 to 80 psi, with 80 psi maximum for rigid PVC and 50 psi maximum for polyethylene. Those are ceilings from that fact sheet, not universal settings. A lower nozzle, valve, drip, or manufacturer limit wins.
A small shop compressor may reach a high gauge pressure without sustaining the required air volume. Raising pressure to compensate is dangerous. Excess air velocity and long dry runs can also heat plastic parts. CSU recommends short passes rather than one long run and warns that pressure-vacuum-breaker and reduced-pressure backflow devices must never be blown through with compressed air.
Call a qualified irrigation contractor when the pipe material is unknown, the system lacks a dedicated connection downstream of the backflow device, the backflow type is uncertain, a pump is involved, valves are damaged, a zone will not open, or the available compressor cannot meet the documented airflow at a safe pressure. A certified backflow tester may be required for service to regulated assemblies.
Protect the backflow device and exposed equipment
The backflow preventer protects the drinking-water supply. Do not disassemble it casually. Local plumbing and water rules can control who may test, repair, remove, or service it. Follow the device manufacturer and water utility.
Rain Bird advises insulating above-ground valves, backflow preventers, the main shutoff, and exposed piping without blocking vents or drain openings. CSU gives device-specific drainage instructions and says some ball valves and test cocks are left half open after draining to avoid trapping water. That position is not a guess to copy onto every assembly; confirm the installed device and its instructions.
If an insulated cover is used, keep required relief and air openings clear. A plastic bag alone can trap moisture and does not replace drainage. Record the final valve positions with photos so spring startup does not begin from memory.
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Cost and quote checklist
Thumbtack’s national planning range for professional sprinkler winterization is $68 to $239. HomeAdvisor reports a typical $56 to $133 range and an average near $91. These are broad planning figures, not bids. Location, zone count, pumps, backflow type, access, repairs, and emergency timing affect the price.
| Quote item | What the written scope should say |
|---|---|
| System coverage | Number of zones, drip circuits, pumps, and detached branches included |
| Backflow work | Device type, drainage steps, insulation, and whether testing or licensed service is separate |
| Blowout method | Connection point, regulated pressure basis, and how each zone is confirmed clear |
| Controller and pump | Final mode, wiring changes, and spring restart notes |
| Closeout record | Leaks or defects found, final valve positions, and items excluded from the price |
Use the contractor quote comparison if prices differ widely. Compare the same zone count and backflow scope before looking at the total.
How to save money without risking the system
Book before the first freeze warning fills the schedule. Give the contractor a zone map, clear access to valve boxes and the controller, and disclose pumps or drip circuits when requesting the price. Ask whether neighbors can schedule adjacent appointments; some local providers price route efficiency into fall work.
Handle low-risk preparation yourself: coil and store hoses with the garden-hose guide, clear vegetation from boxes, label zones, and document existing damage. Do not save money by renting a compressor whose airflow is unknown, bypassing the backflow device, or postponing service until after a freeze.
Keep the closeout record. Next fall, you can request the same scope without paying someone to rediscover every valve and zone.
Winterization closeout checklist
- The dedicated irrigation supply is shut and its location is labeled.
- Every zone and drip circuit is listed on the closeout record.
- The approved drainage or blowout method was completed without exceeding component limits.
- The backflow device was handled under its instructions and local rules.
- Exposed piping is protected without blocked vents or drains.
- The controller and any pump controls are in their documented winter state.
- Hoses, timers, removable filters, and vulnerable accessories are drained or stored.
- Final valve positions and defects are photographed for spring startup.
Sprinkler winterization FAQs
When should I winterize my sprinkler system?
Winterize after the last irrigation of the season and before a hard freeze can reach exposed or buried components. The right week depends on local weather, frost depth, and system design, so use the forecast and local irrigation guidance rather than a national calendar date.
Can I winterize sprinklers without an air compressor?
Only if the installed system was designed to drain fully through manual or automatic drains and the manufacturer or installer confirms that method. Colorado State University Extension warns that shifted pipe and electric valves can retain water, so gravity draining is not a safe assumption for an unknown system.
What pressure should be used to blow out sprinklers?
Use the limits for the pipe, heads, valves, and manufacturer instructions. Colorado State University Extension lists 80 psi as the maximum for rigid PVC and 50 psi for polyethylene, but a lower-rated component controls. Air volume matters too, which is one reason an irrigation professional is often the safer choice.
Should I leave my sprinkler controller plugged in for winter?
Follow the controller and pump instructions. Many controllers can stay powered in Off, Rain, or Winter mode so programs remain saved, but pump-control wiring may need a specific shutdown step. Do not let a controller start a dry pump or reopen a winterized system.
How much does sprinkler winterization cost?
Thumbtack’s national planning range is $68 to $239, while HomeAdvisor reports a typical range of $56 to $133. Zone count, backflow equipment, access, local labor, and repairs can move a quote outside either range, so confirm the written scope.
Frequently Asked Questions
When should I winterize my sprinkler system?
Winterize after the last irrigation of the season and before a hard freeze can reach exposed or buried components. The right week depends on local weather, frost depth, and system design, so use the forecast and local irrigation guidance rather than a national calendar date.
Can I winterize sprinklers without an air compressor?
Only if the installed system was designed to drain fully through manual or automatic drains and the manufacturer or installer confirms that method. Colorado State University Extension warns that shifted pipe and electric valves can retain water, so gravity draining is not a safe assumption for an unknown system.
What pressure should be used to blow out sprinklers?
Use the limits for the pipe, heads, valves, and manufacturer instructions. Colorado State University Extension lists 80 psi as the maximum for rigid PVC and 50 psi for polyethylene, but a lower-rated component controls. Air volume matters too, which is one reason an irrigation professional is often the safer choice.
Should I leave my sprinkler controller plugged in for winter?
Follow the controller and pump instructions. Many controllers can stay powered in Off, Rain, or Winter mode so programs remain saved, but pump-control wiring may need a specific shutdown step. Do not let a controller start a dry pump or reopen a winterized system.
How much does sprinkler winterization cost?
Thumbtack’s national planning range is $68 to $239, while HomeAdvisor reports a typical range of $56 to $133. Zone count, backflow equipment, access, local labor, and repairs can move a quote outside either range, so confirm the written scope.