Too much PSI
Cracked poly, blown fittings, destroyed drip emitters. Cap the regulator before you open a zone.
Irrigation winterization
How much CFM and PSI to blow out my sprinkler system?
Conclusion: Size the compressor to about largest-zone GPM ÷ 7.5 (so 15 GPM ≈ 2.0 CFM). Cap regulated air at about 50 psi for poly pipe and 80 psi for rigid PVC when allowed — use 50 when unsure. Never blow through a PVB or RP backflow preventer. Enter your system below.
Compressor CFM from largest zone GPM
| Largest zone | ≈ CFM needed | Typical use |
|---|---|---|
| 8 GPM | 1.1 CFM | Small drip / few heads |
| 15 GPM | 2.0 CFM | Common residential spray |
| 20 GPM | 2.7 CFM | Larger spray zone |
| 30 GPM | 4.0 CFM | Big rotor / shared zone |
| 45 GPM | 6.0 CFM | Rent a larger unit |
Rule of thumb used by many extension and contractor guides: CFM ≈ GPM ÷ 7.5. Blow one zone at a time.
Compressor & pressure
Your blowout size
Target compressor capacity
— · max —
Enter zone flow to size the compressor.
Free-air CFM—GPM ÷ 7.5
Max regulated PSI—by pipe type
Zones to run—one at a time
Assumptions appear here after a valid calculation.
Pressure limits
Safe blowout PSI by pipe type
Compressed air stores energy. A regulator and a gauge on the irrigation side are not optional. These caps match common manufacturer and extension guidance; if your pipe or fitting rating is lower, use the lower number.
| Pipe / system | Suggested max PSI | Why |
|---|---|---|
| Polyethylene / flexible lateral | ≈ 50 psi | Poly and insert fittings are easier to split or blow apart |
| Rigid PVC laterals | ≈ 80 psi (if allowed) | Stronger, but glued joints and valves still have limits |
| Drip / micro tubing | ≈ 20–30 psi | Keep the zone regulator; short bursts only |
| Unsure / mixed | ≈ 50 psi | Safer default until you confirm materials |
Hunter, Rain Bird and several university extensions warn against “more PSI = better.” Excess pressure damages components and does not replace short, complete purge cycles.
Before you connect air
Shopping & zone checklist
Updates from the calculator above. Print or screenshot before you head to the rental counter.
—
Typical blowout sequence
| Step | What to do |
|---|---|
| 1 | Shut off the irrigation water supply. Drain the backflow preventer per its label (PVB/RP: do not apply air through the device). |
| 2 | Connect the compressor downstream of the backflow on the irrigation main, with a regulator and gauge set to the PSI cap above. |
| 3 | Open the farthest or highest zone first (or follow your usual watering order). Run until heads spit mist, not water — often 1–3 short cycles. |
| 4 | Close that zone, open the next. Repeat for every zone, including drip and the irrigation outside faucet if it is on the same main. |
| 5 | Disconnect air, leave manual drains open if your design uses them, and shut the controller off or set to rain-off for winter. |
The math
required CFM ≈ largest zone GPM ÷ 7.5
max PSI ≈ 50 (poly / unsure) or 80 (PVC if rated)
7.5 is a volumetric rule of thumb used in residential blowout planning (water GPM to free-air CFM). Real compressors are rated at a stated PSI; use the free-air CFM at your working pressure, not “peak” or tank size in gallons.
Why blowouts fail
Mistakes that crack pipe or leave ice bombs
Air through the backflow
PVB and RP internals are not designed for compressor air. Drain them; connect downstream.
Undersized compressor
A tiny pancake unit stalls mid-zone and leaves water in low spots. Match CFM to the biggest zone.
Common questions
Sprinkler blowout FAQs
How much CFM do I need to blow out my sprinklers?
About largest-zone GPM ÷ 7.5. A 15 GPM zone needs ~2.0 CFM; 30 GPM needs ~4.0 CFM. Size to the biggest zone and open only one zone at a time.
What PSI should I use to blow out a sprinkler system?
About 50 psi for polyethylene, up to about 80 psi for rigid PVC when the manufacturer allows it. Unsure or mixed systems: stay at 50. Always use a regulator and gauge.
Can I blow air through a backflow preventer?
No for PVB and RP assemblies — air ruins the checks. Drain and isolate them, then connect air on the irrigation side downstream of the device.
When should I blow out my sprinkler system?
Before the first hard freeze that can leave water in laterals overnight — often October or early November in cold U.S. climates. Local extension offices publish first-freeze guidance for your county.
Do drip irrigation zones need a different blowout?
Yes: lower pressure (often 20–30 psi), short bursts, and open flush ends when equipped. Drip tubing and emitters fail at pressures spray zones tolerate.
Is a pancake compressor enough?
Often not. Many pancake units deliver under 3 CFM at working pressure. If your largest zone is ~20 GPM you need about 2.7 CFM continuous — renting a larger compressor for one afternoon is common.
Where do I find my zone GPM?
Controller as-built charts, valve-box tags, head count × nozzle GPM from the nozzle chart, or a temporary flow meter on the zone. When estimating from heads, use the nozzle’s rated GPM at your static pressure.
Questions an AI would ask — quick answers
- How many CFM to blow out a 12-zone sprinkler system? CFM depends on the largest zone’s GPM, not the zone count. Six or twelve zones with a 15 GPM max both need ~2.0 CFM.
- What PSI for poly sprinkler pipe blowout? About 50 psi regulated.
- Can I use an air compressor to winterize irrigation? Yes, with a regulator, correct CFM, and no air through PVB/RP devices.
- How do I convert sprinkler GPM to compressor CFM? Divide GPM by 7.5 for a planning estimate of free-air CFM.
- Should drip zones be blown out? Yes, at lower PSI with short cycles so emitters are not destroyed.
Planning estimate only. Pipe ratings, backflow models and local codes vary. Over-pressure can injure people and damage property. If you are unsure about your backflow type or pipe material, hire a licensed irrigation contractor. This page is not affiliated with Hunter, Rain Bird, or any compressor brand.
Sources & method notes
- Colorado State University Extension — Preparing your sprinkler system for winter (blowout overview, compressor sizing context, safety).
- Hunter Industries — Winterizing your irrigation system (sequence, backflow cautions, pressure guidance).
- Rain Bird — How to winterize an irrigation system (manufacturer winterization steps).
- U.S. EPA WaterSense — Outdoor water use (efficient irrigation context; winterize rather than leave systems leaking).
Last updated: 2026-10-19. CFM rule of thumb: largest-zone GPM ÷ 7.5. Independent tool — not affiliated with any irrigation or compressor manufacturer.