Sprinkler Blowout & Winterization Denver

Your deadline is set by your address

There is no single blowout date for the Denver metro. There's a rolling one that starts on the Palmer Divide in mid-September and works its way down and east over about three weeks. Monument sits at 6,961 feet and historically takes its first freeze around September 22. Golden and Castle Rock land in the September 28 to 30 range. Denver, Englewood, and Aurora typically hold out until roughly October 4 to 7.

Now the part that trips people up. Longmont and Firestone sit at about 4,970 feet, lower than Denver by 300 feet, and they still freeze around October 1. Flat open ground north of the metro radiates heat away on clear nights with nothing to slow it down. If you moved from a Denver bungalow to a newer build in Erie or Frederick, your old blowout date is now a week late.

Whatever your town's average is, subtract two weeks. That's your appointment. Averages are averages, and a September cold snap on the Front Range is not exotic weather. Every irrigation crew from Longmont to Monument is working the same compressed window, so the calendar fills from the top down.

Getting caught unscheduled with a freeze in the forecast is survivable. Go inside, close the isolation valve that feeds the irrigation stub (usually in the basement or crawlspace near the meter), open the small bleeder cap on it, then go outside and open both test cocks and set the ball valves on the backflow to a 45-degree angle. Water still sits in the laterals. But you've drained and relieved the brass, which is the part that costs real money.

• You're above 6,000 feet in Monument or Castle Rockbook in August for a first-half-of-September slot. Your season is genuinely shorter than the metro's.
• You're in the core metro at 5,200 to 5,500 feetthe last week of September is the sweet spot. Early October is a gamble that mostly pays off, until it doesn't.
• You're leaving town for Octoberget it done before you go. A charged system and an empty house is how a small crack becomes a flooded window well.
• A hard freeze hits before your appointmentshut off, drain, and open the test cocks tonight. Keep the appointment anyway, because the lines still hold water.

What a real blowout involves

The concept is simple: push air through the pipe until water stops coming out of the heads. The execution has a few places to go wrong, and most of them involve the wrong compressor.

Volume is what moves water down a buried lateral, and volume is measured in cubic feet per minute. A tow-behind unit on a trailer moves air by the hundred CFM. The pancake compressor you use for finish nails moves four or five, and it will happily sit there reading 60 psi on the gauge while accomplishing almost nothing except warming up the pipe. High pressure with low volume is the worst combination available: it stresses fittings without clearing them.

Pressure gets held down deliberately. Rigid PVC laterals want to stay under about 50 psi, poly can take a bit more, and blasting past those numbers is how people blow a fitting apart underground in the name of winterizing. Air also goes in downstream of the backflow, never straight through the assembly, because forcing dry air across those internals is hard on the seats and springs you're trying to protect.

A tech works zone by zone, usually starting with the farthest or highest, watching each head fog, then spit, then run dry. Sixty to ninety seconds is plenty. Running air through a bone-dry rotor cooks the gear drive, so short bursts and a second pass beat one long blast every time.

• Isolation valve inside closed, bleeder opened, and the line to the outside relieved
• Air introduced downstream of the backflow, at a blow-out port or quick coupler
• Each zone opened until heads mist, then spit, then run dry, then a second pass
• Ball valves left at 45 degrees and test cocks cracked open so nothing can trap water
• Controller set to off or rain mode; modern timers keep their programs without power