How to winterize a sprinkler system
/This Family Handyman video shows how to blow out a sprinkler system. Draining the lines before the first freeze keeps pipes and the backflow device from cracking.
Video by Family Handyman on YouTube. Watch on YouTube
- How often
- Every fall, before the first freeze
- Video
- 3 min 39 sec
When should you winterize sprinklers in Seattle?
Every fall, before the first freeze. At the University of Washington weather station, Seattle's first fall frost has come as early as October 29 and as late as December 21 since 2012, and outlying areas run earlier; Woodinville has seen frost as early as October 3.
How do you winterize? (Seattle Public Utilities checklist)
- Insulate exposed pipe.
- Turn off the water to the system.
- Drain or blow out the lines (see the methods and safety notes below).
- Open and close the backflow isolation valves to clear the water, leave them semi-open and open the test cocks.
- Turn off the controller and cover the rain sensor.
Drain or blow out?
Systems with manual drain valves can be drained by opening each one; some systems have automatic drain valves at the low point of each zone. Compressed-air blowout is the third method, and university extension services recommend leaving it to a professional because too much pressure can damage the system. Wrap the backflow preventer and above-ground parts in insulation.
Safety notes
- For a blowout, Seattle Public Utilities says to wear eye protection, stand away from heads, stay under 80 psi for PVC and 50 psi for polyethylene, remove the flow sensor first, and never blow air through the backflow device.
Seattle-area notes
Seattle Public Utilities publishes a winterizing checklist for local systems, and the Saving Water Partnership notes fall is the time to shut sprinklers off and let rain take over.
When to call a pro
The University of Minnesota calls a certified irrigation professional the best and safest way to winterize, especially for a compressed-air blowout.
Related guides
Spring sprinkler activation and leak checkInfrared scan for insulation leaksAll Home Care Advice guides
Sources
- WSU King County Extension Tip Sheet 5: frost dates
- Seattle Public Utilities: winterizing and starting up an irrigation system
- Oklahoma State University Extension: winterizing irrigation
- University of Minnesota: preparing irrigation for winter
- Saving Water Partnership: watering schedules
Checked October 2026. Manufacturer instructions for a specific model come first. General information, not a substitute for a licensed professional.
From the Home Care Advice by Brian Huie, a principal broker and Realtor with Compass in Seattle.
