How do you close an in-ground pool for winter?
Updated August 2026
2–3 hours · Moderate DIY
A proper close is 2 to 3 hours of work in a strict order: balance the water, shock and add winter algaecide, drop the level below the skimmer, blow out and plug every line, drain the pump, filter, and heater, then cover it. Sequence matters more than speed, because the damage that ruins a spring opening always traces back to the one line nobody cleared. Do it once the water holds under 60 degrees for a week, and well before the first hard freeze.
What you need
- A test kit or strips plus balancing chemicals
- Winterizing shock and algaecide
- A shop vac or a small compressor
- Expansion plugs for every return, plus a skimmer Gizzmo
- Non-toxic pool antifreeze
- A winter cover with water bags or anchors
Before you start: Pool chemicals are the real hazard in this job. Add chemical to water, never water to chemical, keep shock and acid in separate buckets (mixing them makes chlorine gas), and wear splash goggles and gloves. Kill the pump breaker before you pull a single drain plug. Keep blow-out pressure under 15 psi, because pool plumbing is thin-wall PVC and an expansion plug that lets go becomes a projectile. Leave water in the pool as well: an empty vinyl or fiberglass shell can lift out of saturated ground.
Steps
- Balance the water 3 to 5 days ahead: pH 7.2 to 7.6, alkalinity 80 to 120 ppm, calcium hardness 200 to 400 ppm. Acidic water left under a cover all winter etches plaster and stains a liner.
- Brush the walls, vacuum the floor, and empty both baskets. Organic debris left behind is the fuel for the algae bloom that greets you in April.
- Shock the pool, let it circulate 24 hours, and only then add the winter algaecide. Reverse that order and the free chlorine burns the algaecide off before it can work.
- Clean or backwash the filter, then pull the drain plugs on the pump, filter tank, heater, and chlorinator. Drop the plugs in the pump basket so you can find them in May.
- Lower the water 4 to 6 inches below the skimmer mouth for a solid cover, or to the line the manufacturer specifies for a mesh safety cover. Never drain the pool: ground water pressure can float a shell or collapse a liner.
- Blow the return lines clear with a shop vac on the blow port until steady bubbles come out of each return, then thread in an expansion plug while air is still moving. Keep any compressor under 15 psi on pool plumbing.
- Pour a gallon of non-toxic pool antifreeze into each skimmer and any line you could not fully clear, then set a Gizzmo in the skimmer throat to absorb ice expansion. Automotive antifreeze is toxic and never goes near pool plumbing.
- Pull the ladder, rails, and diving board, plug the anchor sockets, then set the cover and secure it with water bags or anchors spaced about every 4 feet.
Or hire it out
A pool company charges $150–300 to close a standard in-ground pool, more if a safety cover has to be fitted and stored. The comparison that matters: a freeze-cracked pump housing is $150–400 in parts, and a full pump replacement runs $700–1,500 installed.
Done. Now the part everyone skips: doing it again on schedule. Log it in OnOtto and the next reminder for pool closing sets itself.
Log this task, get the next reminderFrequently asked questions
Should I drain the pool for winter?
No. A drained shell has nothing pushing back against the ground water around it, and pools have popped out of the ground or buckled a liner over one wet winter. Lower the level 4 to 6 inches below the skimmer, or leave it near the tile line if you run a Gizzmo and a safety cover. The remaining water also gives the cover something to rest against instead of stretching.
How late in the season can I leave it open?
Close it once the water holds under 60 degrees for about a week, which lands in early October up north and late November in the mid-south. Closing warm water is the classic error: chlorine burns off fast above 60 degrees and the pool turns green under the cover by February. Waiting until after the first hard freeze is the other error, and the expensive one. Regional timing is on how often to winterize a pool.
Do I still need pool antifreeze if I blew the lines out?
Treat it as cheap insurance, not a substitute. A shop vac rarely clears the last cup of water from a long skimmer line or a low spot under the deck, and that cup is enough to split a fitting. A gallon of non-toxic pool antifreeze costs $10–20 and covers one or two lines. Use the pool-rated product only, since automotive antifreeze is toxic to people and pets.