How to Winterize Your Irrigation System in Colorado

Why Winterization Is Non-Negotiable in Colorado

Along the Front Range, overnight temperatures can drop below freezing from mid-September through late May. Water left in irrigation lines, valve boxes, and backflow preventers will freeze, expand, and crack pipes, split heads, and destroy backflow preventers that cost $150–$400 to replace.

A professional winterization typically costs $75–$150 and takes 30–45 minutes. A broken backflow preventer, cracked poly pipe, or split lateral lines can cost $500–$2,000+ to repair in spring.

The Three Winterization Methods

Manual Drain — works only if your system was designed with manual drain valves at the lowest points. Open valves and gravity drains the lines. Not suitable for systems without proper drain valve placement.

Automatic Drain — systems with automatic drain valves that open when pressure drops. Still requires blowing out backflow preventers and valve boxes separately.

Air Blow-Out — the most complete method. Compressed air pushes water out of every zone, head, and fitting. This is the correct approach for most Northern Colorado residential systems.

Air Compressor Requirements

A household air compressor (the 6-gallon shop compressor in your garage) does not have sufficient volume to blow out an irrigation system. You need:

• Minimum CFM: 20–25 cubic feet per minute for residential systems
• PSI setting: 50 PSI maximum for polyethylene pipe (most residential), 80 PSI maximum for PVC

Rent a 185 CFM towable compressor from any equipment rental company for $150–$250 per day, or hire an irrigation contractor who brings their own equipment.

Zone-by-Zone Blow-Out Process

1. Shut off the water supply to the irrigation system at the main shutoff
2. Disable the automatic controller (set to "rain" mode or off)
3. Connect the air compressor to the system's blow-out port or quick coupler
4. Activate Zone 1 at the controller
5. Slowly open the compressor valve — watch for heads to pop up and begin discharging water
6. Run each zone until only mist comes from the heads (approximately 2 minutes)
7. Repeat each zone 2–3 times for thorough removal
8. Never run compressed air through a zone with no heads activated — no outlet means pressure spike

Pro Tip: Work from the zone furthest from the compressor to the zone closest. This ensures you're not pushing moisture back toward zones you've already cleared.

After the Blow-Out

• Leave backflow preventer isolation valves at 45 degrees (half open) through winter
• Open test cocks on the backflow preventer
• Insulate exposed backflow preventers and valve boxes with foam insulation wrap
• Program the controller to the "off" or "winter" setting

Updated on: 29/04/2026