How often should you winterize a pool?
Updated July 2026
In any climate where the ground freezes, winterize an in-ground pool every fall, once, after the water drops below about 60 degrees but before the first hard freeze. The reason is physics: water expands nearly 9% as it freezes, and any left in the pump, filter, or underground plumbing can split a pipe or crack the pump housing. That single oversight is the classic spring surprise, a $500–3,000 repair on cracked lines and a $500–1,200 pump on top. Balance the chemistry, lower the water, blow out and plug the lines, and cover it.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| In-ground pool, freezing climate | Every fall | Water in the lines and pump expands and cracks them at the first freeze |
| Water chemistry | Balance before closing | Balanced winterized water resists staining, scale, and algae for months |
| Water level | Lower below the skimmer | Water in the skimmer throat freezes and cracks the skimmer body |
| Underground plumbing | Blow out and plug the lines | Standing water in buried pipe is the costliest thing to leave |
| Pump and filter | Drain fully, pull the plugs | A cracked pump volute or filter tank is a spring replacement |
| Above-ground pool | Lighter close, no line blowout | Different rules; many run a pillow and cover without a full blowout |
| Warm, no-freeze climate | Do not fully winterize | In the South you keep the pump running at reduced hours all year |
The cost of skipping it
What skipping it costs: a freeze finds every gap you left. Water trapped in the buried suction and return lines expands and splits them underground, and locating and digging up a cracked line runs $500–3,000. A pump left full cracks its housing ($500–1,200 to replace, or $1,000–2,000 for a variable-speed model), and a filter tank can split the same way. Skip the chemistry and you open in spring to a green, stained pool that costs a few hundred dollars in chemicals and days to recover. A proper close is a $150–300 DIY afternoon or a $200–450 pro visit; either beats those bills by an order of magnitude.
How to do it (2–3 hours · DIY, or $200–450 pro)
- Balance the water a few days ahead: pH around 7.2–7.6, alkalinity 80–120 ppm, and a slightly higher calcium and sanitizer level for the long dormancy.
- Clean the pool, then lower the water below the skimmer and return jets, or fit winterizing skimmer plugs.
- Drain the pump, filter, heater, and any chlorinator; pull every drain plug and store the plugs in the pump basket.
- Blow out the plumbing with a shop vac or blower until air bubbles from each return, then plug the lines so no water re-enters.
- Add winterizing chemicals, float an air pillow to absorb ice expansion, and secure a tight cover over the pool.
Knowing the interval is the easy half. OnOtto reminds you at the right interval, and it won't let you snooze it into next year. Tasks persist until they're done, and completing pool winterizing schedules the next one automatically.
Put this on autopilot, free for 30 daysFrequently asked questions
What happens if I do not winterize my pool before a freeze?
The damage is almost always in the plumbing. Water left in the pump, filter, heater, or the pipes buried around the pool expands as it freezes and cracks whatever contains it. A split pump housing is a $500–1,200 replacement, and a cracked underground line is worse, since finding and excavating it can reach $3,000. Even without a burst, skipping the chemistry step leaves you opening in spring to green, algae-filled water that costs hundreds in chemicals to clear. In a freezing climate, a proper close is not optional maintenance.
Can I winterize the pool myself or should I hire a pro?
A homeowner can absolutely close an in-ground pool; the tools are a shop vac or air blower, winterizing plugs, and a chemical kit, for roughly $150–300 the first year. The one step people get wrong is blowing out the lines: every pipe must be cleared of water and plugged, or the freeze still gets you. If your plumbing is complex, or you would rather not gamble a $3,000 pipe repair on a DIY blowout, a pro close at $200–450 is cheap insurance. Many owners DIY once they have watched it done.
When exactly should I close the pool in fall?
Wait until the water temperature holds below about 60 degrees, cold enough that algae goes dormant and your winterizing chemicals last, but close before the first hard freeze threatens the equipment. In much of the North that window is late October into November. Closing too early, while the water is still warm, invites an algae bloom under the cover; closing too late risks a surprise overnight freeze cracking the pump. Watch the forecast and aim for the stretch of cool, above-freezing days that window opens.
Do above-ground and no-freeze pools need the same steps?
No. In a warm, no-freeze climate (much of the South and Southwest) you never fully winterize; you keep the pump running at reduced hours, often 4 to 6 hours a day, and just dial back chemicals for the cooler months. Above-ground pools in cold climates do close, but with lighter steps: lower the water, add an air pillow and cover, and many store the pump and hoses indoors rather than blowing out fixed underground lines. The full line-blowout drill is an in-ground, freezing-climate job.