How to Winterize an Above Ground Pool, Step by Step

To winterize an above ground pool, clean it, balance and shock the water, lower it a few inches below the skimmer and returns, disconnect and drain the pump, filter and hoses, float an air pillow in the middle, and put on a winter cover. A steel- or resin-wall pool stays mostly full all winter; the water holds it in shape.

That’s the whole job. The details below are what decide whether you open to clear water and an intact pool in spring.

Pool closing plannerGet a closing checklist with your shock and balancing doses worked out for your pool.

First: what kind of above ground pool do you have?

How you winterize depends on how the pool is built.

Never fully drain a steel- or resin-wall pool for the winter. Without water pushing out on them, walls can shift or collapse, and an empty liner can shrink or pull out of its track.

When to winterize

Close once the water stays cold, around 60–65 °F, and before your first hard freeze. Trouble Free Pool’s above-ground guide suggests waiting for 60 °F or lower. Algae grows slowly in cold water, so the chlorine you leave behind lasts longer. Close in warm weather and the chlorine runs out early, which is the usual route to a green pool in spring.

What you’ll need

• A winter cover sized for your pool, with its cable and winch, or clips
• An air pillow sized for your pool
• Winter plugs for the return, and a skimmer plug or ice compensator if you plan to plug the skimmer
• Test kit, liquid chlorine, and pH or alkalinity adjusters if your water needs them
• A submersible pump or siphon to lower the water, and later to clear the cover
• Somewhere dry and frost-free to store the pump, hoses and ladder

Step 1: Clean the pool

Skim, brush the walls and floor, and vacuum. Leaves left on the floor feed algae all winter. Empty the skimmer and pump baskets, then clean the filter: backwash a sand filter, or take out a cartridge and hose it off.

Step 2: Balance the water, then shock and hold

Test free chlorine, pH, total alkalinity and CYA (stabilizer). Bring alkalinity into range first if it’s low, then pH to about 7.4–7.6. The pH calculator gives the dose, and the pH guide explains how to add acid safely.

Then raise free chlorine to the shock level for your CYA, about 40% of your CYA reading, and hold it there. For example, a 15 ft round pool filled to 4 ft holds about 5,300 gallons (the above ground pool gallons chart lists every common size); with CYA at 40 ppm, its shock level is 16 ppm. Going from 3 ppm to 16 ppm takes about 88 fl oz, roughly two-thirds of a gallon, of 10% liquid chlorine. That figure comes from our shock calculator, and your own pool size, CYA and product strength will change it. If you don’t know your gallons, the pool volume calculator works them out for round and oval pools.

Keep topping up to the shock level until the water is clear and free chlorine drops by 1 ppm or less overnight. That small overnight loss means nothing in the water is still using up chlorine. The guide to shocking a pool explains the overnight test in more detail.

On closing day, leave free chlorine at the high end of your normal range, and take out any floater or chlorine tablets. Undissolved tablets under a closed cover can bleach and weaken a vinyl liner.

Step 3: Lower the water

Lower the water just below the skimmer and return openings so no water sits in them to freeze. Trouble Free Pool suggests about 6 inches below the lowest opening. Use a submersible pump or a siphon, or set a sand filter to waste if your filter has that setting. To see how much water that is, the pool surface area calculator gives the gallons in each inch of depth for your pool.

There’s another option: leave the level where it is and plug both openings with a skimmer cover plate and return plug. It saves draining, but in places with freeze-thaw cycles, a slow liner leak can drop the water away from a plugged skimmer and let ice pull at the wall there. If you’re not sure, lowering the water is the safer choice.

Either way, check your cover maker’s instructions; some covers need the water at a certain level to support them.

Step 4: Disconnect and drain the equipment

1. Turn off the pump and switch off its breaker or unplug it.
2. Disconnect the hoses from the skimmer, return, pump and filter. Drain them and store them indoors.
3. Drain the pump and filter. Open the drain plugs and let them empty fully. Keep the plugs in the pump basket so you can find them in spring.
4. Store the pump indoors if you can lift it. A frozen pump housing cracks, and replacing one costs far more than an hour of carrying.
5. Sand filter: after draining, set the valve to “winterize” or between positions if your manual says so, so the internal o-rings aren’t under pressure. Cartridge filter: clean the cartridge, let it dry and store it inside.
6. Bring in a salt cell, heater parts and anything else your manuals list.
7. Plug the return with a winter plug, and plug the skimmer or fit an ice compensator in it if you left water in it.

Step 5: Add the air pillow

An air pillow sits in the middle of the pool under the cover. When the surface freezes, the ice pushes toward the pillow instead of out against your walls and skimmer, and the raised middle helps rain and snowmelt run off the cover.

• Inflate it only partway, so it can squash down as the ice pushes on it. A rock-hard pillow is more likely to pop.
• Tie it in the center with cord through its grommets to the top rail on each side. Keep the cords a little loose so they don’t tear the grommets.
• A strip of duct tape over the valve helps it hold air for the winter.

Use a pillow made for pools. Inner tubes and beach balls rarely stay in place or hold up.

Step 6: Put on the winter cover

Spread the cover over the pool and air pillow, then thread the cable through the grommets and tighten it with the winch so the cover sits snug under the top rail. Add cover clips if your pool has them. Remove the ladder before covering, or follow its maker’s instructions for winter.

Over the winter

Every few weeks, and after big storms:

• Pump standing water off the cover, and brush off heavy snow before it piles up.
• Check that the air pillow is still centered and holding air.
• Check the cable or clips. Wind is the most common reason above ground covers come off.
• Look at the water level. A big drop can mean a leak in the liner.

If your winters are mild

Where freezes are rare and short, many owners don’t close the pool at all. They run the pump a few hours a day, keep chlorine in range and brush now and then. If a hard freeze is forecast, run the pump through the night so water keeps moving, and drain the hoses if you’ll be away.

Common mistakes

For inground pools, which need their lines blown out and plugged, see how to close an inground pool.