Typical price of a professional sprinkler blowout in the US; most homes land near $85–$100, with roughly $7–$12 added per extra zone.
AngiWhen to Winterize Sprinklers in Denver, CO
ON TRACK102 days until first 28°F freezeOct 21
In a typical year, winterize your sprinkler system in Denver by October 11. The median first 28°F hard freeze at Denver's NOAA station is October 21 (1991–2020 normals); one year in ten it arrives as early as October 5. Cold deepens quickly here — only about 9 days separate the first frost from that hard freeze.
Oct 11Local deadline
Oct 21Median first 28°F
31 days28°F window spread
41 inSnow per season
OUTLOOK
Typical first first 28°F freeze near Oct 21; local deadline about Oct 11. The live 10-day outlook loads here.
Local freeze dates for Denver
| Threshold | Early (1-in-10) | Median | Late (9-in-10) |
|---|---|---|---|
| 32°F (light freeze) | Sep 28 | Oct 12 | Oct 26 |
| 28°F (hard freeze) | Oct 5 | Oct 21 | Nov 5 |
| 24°F (severe) | Oct 14 | Oct 31 | Nov 14 |
Bars span the early (1-in-10) to late (9-in-10) window for each freeze threshold; the dot marks the median year. The dashed line is the local prep deadline.
NOAA station: Denver Water Dept · 1.2 mi away · 5,228 ft elevation.
- Denver sits in the middle of the pack, with a mid-fall first freeze — don't let a mild stretch push the work later.
- Elevation here is about 5,228 feet; on calm nights, valley bottoms and low yards can read several degrees below the station, so build in a buffer.
Numbers for Denver come from Denver Water Dept, 1.2 miles away at 5,228 feet, where the medians fall 32°F by Oct 12, 28°F by Oct 21, 24°F by Oct 31. Year to year the 28°F date has ranged from Oct 5 to Nov 5 — about 31 days apart. Spring's last 32°F freeze clears around Apr 30. Snowfall averages 41 inches a year, first reaching an inch near October.
Denver usually sees its first 32°F night about Oct 12, with the first 28°F hard freeze close behind near Oct 21. The 32°F date swings from Sep 28 at its earliest to Oct 26 at its latest, near 28 days. The last spring freeze averages Apr 30 and as late as May 13, which sets the safe window for reopening outdoor water and de-winterizing gear. Roughly 41 inches of snow fall in an average year, so a clear roof edge and a running snow blower matter as much as the freeze itself.
Your sprinklers checklist
- Shut off the irrigation water supply at the main valve and, if you have one, the dedicated sprinkler shutoff inside the house.
- Turn off the controller or set it to the "rain" mode so valves do not open while the system is dry.
- Drain the mainline using the manual, automatic, or blow-out method your system was built for; most pros prefer a blow-out.
- Connect a compressor to the blow-out port through a proper adapter and run 40–80 psi, one zone at a time, until the heads mist and clear.Helpful gear: Air compressor blow-out adapter — Recommended pick
- Insulate the backflow preventer and any above-ground valves; this brass assembly is usually the first part to crack.Helpful gear: Insulated backflow preventer cover — Recommended pick
- Cap outdoor hose bibs with foam covers after the hoses come off so the last exposed fittings stay protected.Helpful gear: Foam outdoor faucet covers — Recommended pick
- Open the backflow test cocks a quarter turn so any trapped water has room to expand.
- Log the date and the psi you used; you will want the reference next fall.
What to have on hand
As an Amazon Associate we may earn from qualifying purchases. Product picks are editorial; links do not change what you pay.
Air compressor blow-out adapter
Quick-connect fitting that mates a shop compressor to your irrigation line.
Recommended pickInsulated backflow preventer cover
Pouch that shields the above-ground backflow valve from early frost.
Recommended pickFoam outdoor faucet covers
Slip-on domes that protect hose bibs after you drain them.
Recommended pickPortable air compressor
A modest pancake unit moves enough air to clear most home zones.
Recommended pickSprinkler blowout cost & key numbers
Verified national benchmarks; sources open in a new tab (nofollow).
Maximum safe blow-out pressure for flexible polyethylene pipe (≤80 PSI for rigid PVC). Air volume does the real work — about 20–25 CFM clears a residential zone.
Colorado State University ExtensionReplacement cost of a freeze-cracked backflow preventer — the brass assembly cannot be repaired once ice splits the body, and freeze damage voids most device warranties.
PlumbingPriceGuideHow much water expands when it freezes — enough force inside a charged line to split fittings, valves and the backflow body over a single hard night.
EPA WaterSenseWhat this means locally
Compared with nearby cities, Denver's first-freeze date near Oct 21 sits later than Lakewood (Oct 16) and close to Commerce City (Oct 18). Colorado's deadlines span Sep 30 to Oct 23 statewide — one date for all of Colorado would be off by weeks for Denver. Once you know Denver's freeze date, use it to protect your indoor pipes and winterize an RV if you own one too. Keeping an eye on the rest of the county? The same local math is on our Fort Collins page.
Other winter jobs in Denver
Every task below is dated to Denver's own freeze and snow normals.
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Frequently asked questions
What temperature freezes sprinkler pipes?
Standing water in shallow lines and the backflow assembly can start to freeze once air temperatures drop into the mid-20s for several hours. Buried mains are slower, but the exposed brass backflow preventer and above-ground valves are the parts that crack first, which is why the deadline is tied to the first 28°F freeze, not the first frost.
Do I need to blow out my sprinklers or just drain them?
It depends on how the system was installed. Manual or automatic drains work if the lines were pitched to low points. Most irrigation pros recommend a compressed-air blow-out because it clears water that drains miss, especially in flat yards. If you are unsure how your system drains, a blow-out is the safer choice.
What happens if I don't winterize my sprinkler system?
Water left in the lines expands as it freezes and can split the backflow preventer, crack valves, or break fittings. Repairs to a backflow assembly commonly run more than the cost of a blow-out. The damage often is not visible until you turn the system on in spring and find leaks.
How much does a sprinkler blowout cost?
A professional blow-out typically costs somewhere in the range of a modest service call, depending on the number of zones and your region. Buying an adapter and using your own compressor costs less over time, but you need enough air volume to clear each zone. Prices rise once the first freeze warnings appear, so book early.
When should I turn my sprinklers back on in Denver?
Wait until the last spring freeze has passed, which averages around Apr 30 here in the 1991–2020 normals. Turning the system on too early risks refreezing a charged line. Open the main slowly to avoid a pressure surge, then walk each zone to check for winter damage before you rely on the schedule.
Can I winterize sprinklers myself?
Draining and insulating are within reach for most homeowners. A blow-out is doable if you own a compressor that moves enough air and you use a proper adapter, working one zone at a time at safe pressure. If your system lacks a clear blow-out port or you are not confident, hiring a pro once is a reasonable call.
How many PSI do I need to blow out my sprinkler system?
Use a regulated 40–60 PSI for most residential systems, and never exceed 50 PSI on flexible polyethylene pipe or 80 PSI on rigid PVC — more pressure can crack pipes and shred sprinkler seals. Air volume matters more than pressure: about 20–25 CFM moves the water out, while a small pancake compressor needs several short passes per zone.
Do I need to winterize the backflow preventer too?
Yes — it is the most expensive single component at risk. Drain it fully, leave the test cocks and ball valves at a 45° half-open angle for winter, and never force compressed air directly through a pressure vacuum breaker, which can destroy its internal seals. A freeze-cracked unit cannot be repaired and costs $200–$1,800 to replace.
Sprinkler Winterization: related searches
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Data: NOAA 1991–2020 normals via Denver Water Dept, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 25, 2026.