Irrigation System Winterization: Step-by-Step Blowout Guide

When temperatures start dropping, irrigation systems need to come down for the season. In climates where the ground freezes, leaving water in the lines is not a calculated risk — it is a guaranteed repair bill. The steps below outline the air blowout method, which is the most reliable and widely used approach for residential and light commercial systems.

Before You Start

Some systems are marketed as self-draining. That designation does not eliminate the need for winterization. Drain valves can clog, get left open or fail to clear low spots in the line. The time and equipment cost of blowing out a system is small compared with replacing cracked fittings and split pipe in the spring.

Step-by-Step Winterization Procedure

Shut Off the Water Supply. Locate the master shutoff valve for the irrigation system — typically in the basement, crawl space or utility room. Close it completely. Tag the valve so it is not accidentally reopened by someone unfamiliar with the system.
Manually Drain the System. Open a hose bib or the drain on the backflow preventer to bleed pressure and drain as much standing water as possible before connecting the compressor. Use a bucket. Opening a pressurized drain will push water out hard for the first few seconds.
Set Up the Compressor. The minimum recommendation for most residential systems is 60 PSI at 15 cubic feet per minute (CFM). Connect the compressor to the system through an accessible hose bib or drain port downstream of the main shutoff. Maximum operating pressure during blowout should not exceed 80 PSI. Excess pressure can damage sprinkler heads, rotors and pipe fittings.
Blow Out Each Zone. Start with the zone furthest from the main connection, or the zone at the highest elevation. Activate that zone at the controller for approximately two minutes, then watch the heads. Once the air output is dry, that zone is clear. Move to the next zone and repeat. Run each zone twice in short cycles rather than once in a long cycle.
Inspect the Backflow Preventer. After completing all zones, verify the backflow preventer is fully drained. Open all drain ports on the device. Over winter, leave ball valves set to a 45-degree angle rather than fully open or fully closed.

Timing and Scope

A standard residential system takes 30 to 45 minutes to winterize with an appropriately sized compressor. Larger systems, pumps, fertilizer injectors and ancillary equipment add time.

Systems with low-lying runs, multiple elevation changes or older components benefit from a qualified walkthrough before the shutdown to flag anything that needs attention before spring.