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How to winterize and blow out a sprinkler system in Ontario

In the GTA the ground can freeze below the depth of irrigation lines. Any water left in pipes, valves or the backflow device expands as it freezes and cracks them. Winterizing means shutting off the supply and pushing every drop out with compressed air before the first hard frost — usually mid-October to early November.

Step by step

  1. 1

    Shut off the irrigation water supply

    Close the dedicated irrigation shut-off valve inside the house, usually near the water meter.

  2. 2

    Turn the controller off

    Set the controller to Off or Rain mode so it does not open valves while you work.

  3. 3

    Connect the compressor

    Attach the air compressor to the blowout port or the test cock after the backflow device using a proper adapter.

  4. 4

    Blow out one zone at a time

    Open a single zone from the controller, then slowly add air. Keep pressure moderate (generally no more than about 50 psi for poly pipe, 80 psi for PVC) and stop when only mist comes from the heads.

  5. 5

    Cycle through every zone twice

    Move zone to zone, then repeat the whole sequence. Never run air through a closed system — at least one valve must be open.

  6. 6

    Drain and protect the backflow

    Open the backflow test cocks and leave them at 45 degrees, and drain the outdoor supply line so nothing freezes in the house wall.

What you need

A compressor with enough volume (CFM) matters more than peak pressure. Small pancake compressors run out of air and leave water in the far ends of long zones.

  • Air compressor with a regulator
  • Blowout adapter for your backflow or blowout port
  • Safety glasses
  • Access to the controller

Mistakes that cause spring repairs

Most spring repair calls we see trace back to one of these:

  • Too much pressure — heads blow apart and fittings separate underground
  • Running air with every valve closed — overheats and damages valves
  • Skipping the backflow drain — the brass body cracks
  • Only one pass per zone — water settles back into low spots

When to hire it out

If you don't own a large compressor, have a long or multi-zone system, or aren't sure where your blowout point is, a professional winterization is usually cheaper than renting equipment and far cheaper than replacing a cracked backflow or valve manifold.

Common questions

When should I blow out my sprinkler system in the GTA?
Aim for mid-October to early November, before overnight temperatures stay below freezing.
Can I just drain the system instead of blowing it out?
Only systems built with manual or automatic drain valves can be drained. Most GTA systems need compressed air to clear the lateral lines.
What does professional winterization cost?
Our standard residential winterization is $99 plus HST; larger systems are quoted on site.
Book a $99 winterizationInstant estimate

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