Winterizing Your Sprinkler System Without Blowout: An Effective Alternative Approach

For homeowners in mild-climate regions, blowing out the sprinkler system with a compressor every fall is overkill — and, if done incorrectly, carries its own risk of damage. If your system and climate meet the right criteria, draining without a blowout is a perfectly reliable winterization method. This guide explains exactly who it works for, what you'll need, and how to do it step by step.

Is the No-Blowout Method Right for Your System?

This method is a confident, complete solution for systems that meet all four of these criteria. If any one is absent, use the compressor blowout method instead.

1. Mild climate (USDA Hardiness Zones 8–10) These zones cover most of the Pacific Coast, the Gulf Coast, southern Arizona, and the lower Southeast. Winter lows in these zones rarely drop below 20°F (-7°C), and when they do, it's brief — a few hours, not sustained days. A properly drained and insulated system handles that without issue. If you're in Zone 7 or colder (most of the Midwest, Northeast, and Mountain states), use a compressor blowout — sustained hard freezes will crack pipes that still hold any water.

2. Your system has drain valves at zone low points This method relies on drain valves — either manual or automatic — installed at the low point of each irrigation zone. These are what actually remove the water; insulation alone is not enough. If your system doesn't have drain valves, this method won't work regardless of your climate.

• Manual drain valves are opened by hand or with a screwdriver and must be closed again in spring.
• Automatic drain valves open on their own when water pressure drops below 2–3 PSI, meaning the act of shutting off the main supply triggers drainage automatically.

If you're unsure whether your system has drain valves, look for small valve housings at the far end or lowest point of each lateral line, often just below a sprinkler head or at a T-junction.

3. Your system has air relief (air-vacuum) valves at zone high points This criterion is just as important as the drain valves — and often overlooked. When water drains out of a closed pipe through the low-point valve, air must enter from above to replace it. Without air entry, a vacuum forms inside the pipe, stalling drainage and leaving water trapped at mid-line elevations where it can freeze. Air relief valves — installed at the high point of each zone — break that vacuum automatically as pressure drops. They open with an audible click or hiss as the water level falls past them.

If your system has drain valves but no air relief valves, gravity drainage will be incomplete. Do not rely on this method in that case. A qualified irrigation technician can confirm whether your system has air relief valves; they are typically small inline valves positioned at zone peaks, sometimes housed in a small green plastic body flush with the ground.

4. Your pipe runs slope toward the drain valves Water only drains by gravity. If any section of your lateral pipe runs flat or uphill relative to the drain valve, water will pool in that section and freeze. If your system was installed with a consistent downward slope to the low-point valves, you're in good shape. If it wasn't — or if you don't know — a blowout is safer.

All four criteria apply to your system? Read on.

Why Both Valves Are Required

Water trapped in a sealed pipe cannot drain under gravity alone — as it exits through the low-point drain valve, it creates a partial vacuum above it that holds the remaining water in place. Air relief valves at the zone high points break that vacuum by admitting air, allowing water to fall freely to the drain. A system with only one of these components will not fully drain.

What You'll Need

Gather these before you start:

• Flathead screwdriver — for manual drain valves (most use a ¼-turn slotted head)
• Foam pipe insulation sleeves — sized to your pipe's outer diameter (common: ¾" or 1"); choose R-4 or higher for exposed above-ground sections
• Duct tape or zip ties — to secure insulation seams and ends
• Insulated backflow preventer cover — a commercial cover rated to at least 10°F (-12°C); sized to fit your preventer model
• Sprinkler head covers — hard plastic dome covers designed to sit over heads; optional but useful in areas that see occasional frost
• Valve key (if your manual drain valves are key-operated rather than slotted)

Steps to Winterize Without a Blowout

1. Shut Off the Main Water Supply

Locate the shutoff valve for your irrigation system — this is usually a dedicated ball valve or gate valve on the supply line to the system, separate from your home's main water supply. Turn it fully off. If your shutoff is a ball valve, the handle should be perpendicular to the pipe when closed.

Do not skip this step or assume turning off the controller is sufficient. The controller only stops activation; it does not stop pressurized water from sitting in the lines.

2. Disable the Irrigation Controller

Set your controller (timer) to Rain, Off, or Seasonal Adjustment: 0% — whichever your model supports. The goal is to prevent any zone from activating on a schedule while the system is drained and open.

• Rain/Sensor mode: The controller keeps its schedule but will not activate zones. Preferred because your schedule is preserved for spring.
• System Off: Completely disables all scheduled runs.
• Seasonal Adjustment at 0%: Keeps the schedule active but runs zero minutes — another clean option.

Do not simply unplug the controller if it requires a battery to retain its program — you'll lose your entire zone schedule and have to reprogram in spring.

3. Open the Zone Drain Valves and Confirm Air Relief

With water supply off, open the drain valve at the low point of each zone:

• Manual drain valves: Insert a flathead screwdriver into the slotted head and turn ¼ turn counterclockwise. You'll hear or see a small amount of water discharge. Leave the valve open for the entire winter — close it again only in spring before reopening the water supply.
• Automatic drain valves: These opened on their own the moment pressure dropped when you closed the main shutoff. Confirm drainage by checking that the valve housing is no longer pressurized (press the small test pin if present — no water should spray out).

As drainage begins, the air relief valves at the zone high points should open automatically. You may hear a faint click or brief hiss from the high-point area as air enters the line — this is normal and confirms the vacuum is broken and water is flowing freely toward the drain. If you hear nothing and drainage seems slow or incomplete, the air relief valve may be stuck or absent; do not assume the zone is clear.

Work zone by zone. If a manual drain valve doesn't produce flow, the pipe may not slope toward it — flag that zone for professional evaluation before the first hard frost.

4. Insulate Exposed Pipes and Risers

Any pipe or riser that runs above ground is vulnerable to a frost event even in Zone 8–10. Insulate all of them:

1. Measure the outside diameter of the exposed pipe or riser.
2. Cut foam insulation sleeves to length with scissors or a utility knife.
3. Slip the sleeve over the pipe, closing the pre-cut slit around it.
4. Secure the seam and any butt joints with duct tape every 6 inches.
5. Pay particular attention to the section of riser between the soil surface and the sprinkler head — this short section is the most exposed.

Use R-4 or higher rated foam (polyethylene foam insulation commonly sold in the plumbing aisle). For zones that see occasional frost, consider wrapping a second layer on risers taller than 6 inches.

5. Protect the Backflow Preventer

The backflow preventer is the most vulnerable above-ground component — it contains multiple internal chambers that trap water and crack easily in a freeze. Insulating it properly is non-negotiable.

Use a purpose-made insulated backflow preventer cover, not a towel or burlap sack. Towels absorb moisture and hold it against the device, which can accelerate freeze damage on cold nights. Commercial insulated covers are inexpensive ($15–$30), rated by minimum temperature, and designed to fit the most common preventer sizes (Watts, Febco, Wilkins). Match the cover to your minimum expected winter temperature — not your average low.

To install: open the cover, wrap it snugly around the preventer assembly including all exposed fittings, and secure the fastening strap or zipper. The preventer should be fully enclosed with no gaps at the top or bottom.

6. Cover Sprinkler Heads

Install hard plastic protective dome covers over each sprinkler head. These snap or twist over the top of the head and protect the internal wiper seal from freezing debris and frost. They are sold at irrigation suppliers and most hardware stores.

If your system has pop-up heads that retract fully below grade when not pressurized, covering them is optional — they're largely protected by the surrounding soil. Rotary heads and any head with an above-grade body benefit most from covers.

7. Store Hoses and Mark the System

Disconnect any hoses from outdoor faucets and store them coiled in a garage or shed. Water left in a hose that's connected to a faucet can back-siphon into the supply line and create a freezing risk at the connection point.

If any part of your system is buried at shallow depth or in areas where you'll be doing winter digging, landscaping, or snow removal, mark the location of heads and valve boxes with stakes or flags to avoid accidental damage.

Climate Scope and When to Use a Blowout Instead

This method is designed for mild-winter regions — USDA Hardiness Zones 8–10 — where freezing temperatures are shallow and infrequent. In these climates, a properly drained and insulated system faces frost events measured in hours, not days, and can handle them without issue.

If you are in Zone 7 or colder, or your region experiences sustained freezing temperatures or deep ground frost, use a compressor blowout regardless of whether your system has drain and air relief valves. Gravity drainage removes the bulk of the water but not every drop. In sustained freeze conditions, residual moisture in fittings, valve bodies, and sprinkler heads is enough to cause cracking. A blowout is the only method that removes enough water to be safe in those conditions.

Not sure which method fits your situation? Use this table:

The no-blowout method is not a lesser alternative — it's the right method when the system was designed for it. In mild climates with fully draining systems, a compressor blowout offers no meaningful benefit and adds the risk of seal damage from over-pressurization if done incorrectly. Choose based on your system's design and your climate, not habit.

Conclusion

If your system has low-point drain valves, high-point air relief valves, properly sloped pipe runs, and you're in USDA Zone 8–10, you have everything you need to winterize without a blowout — no compressor rental, no contractor visit required. The drain valves release the water; the air relief valves let air in to replace it. Together, they do the work completely.

Shut off the supply, disable the controller, open the drain valves, confirm the air relief valves responded, insulate exposed components, and you're done. Come spring, close the drain valves, re-enable the controller, and turn the water back on. A system designed for drainage performs this process reliably year after year.