New Hampshire irrigation systems must be shut down before the temperature goes below 30 degrees.
If an irrigation system is not properly shutdown is exposed to temperatures below 30 degrees for an extended period of time, you most likely will have damage to your backflow system. From there it would move into control valves and manifolds. Potentially it could damage sprinkler heads. Pipes and fittings could get damaged.
For winter shutdown, we blow compressed air through all of the lines to remove all of the water. We remove water from the backflow, valves and heads. The water inside is removed so that it can’t freeze.