How to Winterize Your Swimming Pool

winterize a pool

After long summer days of lazing in and around your pool, you probably hate to see the coming of cold weather. The changing season also means performing all those little tasks that prepare your home for winter, from raking up fallen leaves to winterizing your swimming pool.

While closing up your pool definitely takes more time and hassle than opening it in the spring or maintaining it in the summer, when done properly, it makes your springtime work easier and helps prevent costly weather damage to the pool. Whether you have an in-ground or above-ground pool, here’s what you need to know.

Preparing to Close Your Pool

Before you begin closing up your pool, first inspect it carefully and test it to ensure it’s free of leaks. One of the greatest dangers to above-ground pools in particular is wintertime leaking. As ice forms on top of the pool’s water surface, it grips the walls. If the liner or sides leak, the water level beneath – which should support the ice above – gradually drops. Disaster waits to strike in the spring as the ice thaws, loses its grip on the walls and smashes to the pool bottom. The liner can be completely ruined and the walls crimped, leaving you with an expensive problem.

If you have a patio, deck or platform built around your pool, sweep it clean of dirt, leaves and other debris that may contaminate your pool water.

An easy way to test for small leaks is to measure the exact depth of the pool water and record it or mark the level on the side of the pool. Place a bucket or pan full of water beside the pool. Mark or record its depth as well. With the pool undisturbed – no swimming, skimming, filtering or any other activity – wait 24 hours. Check the level of the water in both the pool and the container. Both should vary from their original depth by the same amount since they are subject to the same conditions. If the pool is lower than the container, you have a leak. Address the issue before proceeding to winterizing.

If you have a patio, deck or platform built around your pool, sweep it clean of dirt, leaves and other debris that may contaminate your pool water. Remove any poolside furniture and store in a protected area. Alternatively, cover furniture with durable, waterproof coverings. Also, prepare your pool cover. Purchase a new one (typically about 3 or 4 feet wider than the pool circumference or edges to allow it to hang over the sides) or remove a used one from storage. Check for holes and tears and clean it if necessary before using.

Swimming Pool Winterization

In most parts of the country, winterizing your pool is essential to avoid not only structural damage but equipment failure. Pool owners in less seasonal climates, such as in Southern California and Florida, may be able to skip these measures and adopt a winter maintenance schedule instead. Before closing your pool, consult your owner’s manual or the manufacturer to determine any special needs or requirements.

Turn off the pool heater. Look for the heater inline with the pump and filter.

Remove pool accessories. Stairs, ladders, rafts, toys and other items should be cleaned and stored properly to protect them through the winter season.

Chemically balance the pool water. Starting the winter with the proper chemicals helps protect your pool from scale (hard water buildup) and corrosion. Test and adjust the pH, calcium hardness, chlorine and total alkalinity levels as necessary. See the water specifications in the FAQ below for more information.

Shock the water. Add a shock product, following the product instructions to determine the proper amount according to the pool size. Shock raises the chlorine levels. See the chlorine specifications listed in the FAQ below for further information.

Run the filter. Allow the pump and filter to run for several hours – a minimum of eight to 12 if possible.

Clean the pool. Wipe down or brush the sides first and then the pool floor to loosen dirt, algae and other contaminants. Skim the surface of the water and vacuum the floor to remove the debris. When left in your pool, algae and other contaminants can stain the surfaces and leave lasting damage.

Add winterizing chemicals if preferred. Specially packaged pool chemicals for winter closing make it simple to add the included items according to the pool size. Broadcast these chemicals from the deep end or by walking around the pool. More information about winterizing chemicals is provided in the FAQ below.

Clean the pool equipment. Remove remaining chlorine from the chlorinator. Clean out the skimmer basket. Backwash or clean the filter to type: Both cartridge filters and D.E. grids – filters made with diatomaceous earth – can be flushed thoroughly with a garden hose fitted with a sprayer nozzle to create enough water pressure to remove contaminants. Sand filters, on the other hand, require backwashing according to the manufacturer’s instructions.

Lower the water level. With above-ground pools, you must lower the water to allow you to remove the pump. Drain to below the return line, but never more than 18 inches to prevent stress on the pool cover. To prevent structural damage, never completely empty your above-ground pool.

For in-ground pools, lowering the water level protects tile rims and is always necessary in that instance. It also helps prevent pool water from entering the water line. To lower the water level, drain or pump out enough to clear the return inlet (where water enters the pool) and the skimmer, if present. Alternatively, use a specially designed skimmer guard that covers it and makes it watertight.

Winterize your pool pump and water lines. If you have an above-ground pool, you likely can thoroughly drain your pump and store it in a protected shelter. Remove the flexible water hoses and cap the water line openings to prevent drainage.

For in-ground pools, either use pool antifreeze (NOT car antifreeze!) or blow out all valves and water lines with either a powerful reverse vacuum or an air compressor. You can also use both in combination, first blowing and then cycling antifreeze through your lines. For antifreeze, add the product as instructed and circulate at least two minutes or as directed. Plug all lines with special winterizing plugs. Finally, blow out the drain underneath the pool from the opposite end before capping. When bubbles appear, immediately cap the drain line. The vapor lock caused will prevent the drain from gathering water and freezing in harsh climates.

Whether you have an in-ground or above-ground pool, consult your equipment manufacturer or product owners manual for specific instructions. Alternatively, contact a local pool professional for questions relating to the climate in which you live and how it affects your pool.

Turn off the power supply. Shut off any timers, flip electrical switches, unplug any power cords, and turn off the circuit breaker controlling your pool equipment.

Retest the chemical levels. Adjust as necessary to ensure everything is stable.

Protect your metal. Permanent ladders, railing and other metal items may rust in winter. Either wrap them in duct tape or coat with a generous layer of petroleum jelly to protect them.

Cover the pool. Select either a mesh or waterproof cover according to your preferences. Make sure to use an oversized cover to allow you to overlap the pool sides. Secure as necessary – water bags or sandbags are often placed on top or around the pool edge. Alternatively, use a cable tie-down system to ensure the cover is tight and unlikely to move for any reason.

If you have lowered your pool water level, create a support for the pool cover. When loaded with snow, ice or even covered with water, it can get very heavy. To support the pool cover, blow up air pillows and place them in the center of the pool. You can also use tires, balls, rafts and other floating objects. As a side benefit, these items allow the ice to expand without exerting as much pressure on the pool wall.

Closing Your Swimming Pool: FAQ

In addition to knowing the basic steps to winterize your swimming pool, you may have questions about some of the details. Here are some commonly asked questions that will help you close your pool.

When should I winterize my pool? The ideal time to close your pool is when the temperatures are in the 60s and 70s during the day and in the 40s during the night – usually around mid-October in many parts of the United States. Lower outdoor temperatures help ensure the chlorine and other chemicals won’t dissipate as quickly.

I live in a mild climate. Do I still need to winterize my pool? In the southernmost regions of the country, it rarely freezes, so there’s little danger of your pool freezing. In these areas, continue cleaning and vacuuming your pool as needed and run the filter at least twice daily. Test and adjust the water regularly, as needed. Essentially, the pool needs lighter maintenance than when it was being used for warm weather, but you must keep it clean and the water circulating.

How do I balance my chemicals? Choose from a variety of testing kits. Read the instructions carefully as the exact testing procedure varies according to the kit. Aim for ideal chemical levels of:

  • pH: 7.2 to 7.6
  • Alkalinity: 80 to 120 parts per million
  • Calcium hardness: 175 to 250 parts per million
  • Chlorine: 1 to 3 parts per million (Slightly over 3 ppm is great for wintertime.)
  • A variety of agents will adjust these chemical levels. Consult your local pool supplier for more information.

What are winterizing chemicals? Winterizing chemicals are designed to help protect your pool water quality during the winter, leaving it ready to open in the spring. Most of these chemicals aren’t regularly added to your pool water. You can buy each separately or in a kit sized to your pool capacity. The chemicals include shock (often chlorine-free) as well as an oxidizer (also chlorine-free), winterizing algaecides, stain removers and other ingredients. Are they really necessary? Probably not in most circumstances. However, if you prefer peace of mind, they are an option.

Is the antifreeze safe? If you purchase pool antifreeze, it’s completely nontoxic. It does help prevent your lines from freezing, like automotive antifreeze protects your car. However, it will get into your swimming pool water when you reopen it in spring. For this reason, some professionals prefer to avoid using antifreeze. If you are confident you were able to blow all water out of every line, feel free to skip it. Otherwise, any bit of water remaining may cause a problem in the deepest part of winter.

When should I open my pool again? How long your water will stay balanced and clean depends on the cover and other environmental factors. Typically, the pool water will remain clear until April or May, depending on the location and climate. To avoid green, swampy water, uncover your pool and perform your opening maintenance no later than mid-May. Add a strong amount of shock two or three weeks before opening to improve the water clarity when you start.