Knowing how to winterize a pool helps protect it from Illinois’ freezing winter temperatures. Water left in plumbing or equipment can freeze, expand, and cause costly damage. Proper preparation also makes reopening your pool easier in spring.

Aqua Pools helps Illinois homeowners prepare their pools for changing seasonal conditions. This guide covers winterizing in-ground, above-ground, and saltwater pools, including chemicals, equipment, common mistakes, and professional closing options.

Quick Answer: How to winterize a pool?

1. Prepare the pool: Clean the pool and test and balance the water.
2. Protect plumbing and equipment: Blow out and plug applicable lines, then drain and winterize the pumps, filters, and other equipment.
3. Cover the pool: Remove ladders and other accessories as needed, then install and secure the appropriate winter cover. We may also add closing chemicals if needed.

Why Winterizing Your Pool Matters (Especially in Illinois)

Illinois winters bring freezing temperatures that put your pool’s plumbing, equipment, water, and surfaces at risk. Proper winterization helps prevent damage and keeps the pool in better condition for spring.

• Freeze damage: Water left in plumbing, pumps, filters, or other equipment can freeze and expand, potentially damaging components.
• Algae growth: Improperly prepared water can encourage algae growth during the off-season, creating more cleanup when you reopen the pool.
• Liner and surface problems: Unbalanced water chemistry can affect pool liners and surfaces while the pool is closed.

When Should Illinois Pool Owners Close Their Pool?

Use water temperature and weather conditions, not a fixed calendar date, to decide when to close your pool. Closing while the water is too warm can encourage algae growth, while waiting too long risks freezing weather arriving before winterization is complete.

What Happens If You Skip Winterization?

Water expands when it freezes, putting pressure on plumbing, fittings, pumps, and filters when water gets stuck inside. Skipping or improperly completing winterization can also lead to algae growth and more cleaning, chemical treatment, and maintenance in spring.

Pool Closing Chemicals: What You Need and How to Use Them

Balance your pool water before adding winterizing chemicals. While exact needs vary by pool and product, these five steps cover the basics:

1. Balance pH: Aim for a pH of 7.2–7.8 before closing. If the pH is too high, muriatic acid can help lower it when used according to product directions.
2. Check total alkalinity: A range of 80–120 ppm helps stabilize pH. Adjust as needed before moving on to other treatments.
3. Check calcium hardness: Proper calcium hardness helps protect pool surfaces and equipment. Recommended levels can vary by pool surface, so follow the guidance for your pool.
4. Shock the pool: Use an appropriate pool shock and follow the product’s dosage instructions for your pool size. Allow it to circulate as directed.
5. Add winter algaecide if needed: Winter algaecide can help control algae during the off-season. Follow product directions, especially for timing when using it with chlorine shock.

What Order Do You Add Pool Closing Chemicals?

Start by testing and balancing the water, then shock the pool and add other winterizing treatments as directed. Allow enough circulation time between products when required, since application order and timing can vary.

How Long to Run the Pump After Adding Chemicals?

Run the pump long enough to circulate each chemical according to its product instructions. Complete the recommended circulation period before winterizing the equipment and installing the pool cover.

How to Winterize an Inground Pool

If you’re learning how to winterize an in-ground pool, follow these steps to protect the water, plumbing, equipment, and pool structure from freezing conditions.

Step 1 — Lower the Water Level

Lower the water as needed based on your skimmer, pool, and winter cover system. Avoid completely draining the pool unless a professional or the manufacturer directs you to, as improper draining can damage the liner or pool structure.

Step 2 — Blow Out and Plug the Plumbing Lines

Clear water from applicable plumbing lines so it can’t freeze and damage pipes or fittings. Once cleared, protect the lines from water re-entry using the appropriate method for your pool setup. You may also use pool-safe pool antifreeze when appropriate.

Step 3 — Remove, Clean, and Store Equipment

Remove and store seasonal accessories, then clean and prepare your filter, pump, heater, and other pool equipment according to manufacturer instructions. Drain components as required so water isn’t left inside to freeze.

Step 4 — Install the Winter Cover

Install a properly sized mesh or solid winter cover using its intended anchoring system. Mesh covers allow precipitation to pass through, while solid covers block more water and debris but may require standing-water maintenance. Follow the manufacturer’s installation and winter-care instructions for your specific cover.

How to Winterize an Above-Ground Pool (Including Intex)

Learning how to winterize a pool above ground involves slightly different steps than winterizing an in-ground pool.

Above-Ground Pool Closing Steps (Standard Steel/Resin Frame Pools)

1. Blow out and plug the lines: Clear water from the plumbing lines and plug them to help protect against freezing during winter.
2. Winterize the equipment: Drain and prepare the pump, filter, and other pool equipment for freezing temperatures and the off-season.
3. Remove ladders and handrails: Remove and store ladders, handrails, and other accessories as needed before covering the pool.
4. Install the winter cover: Secure a properly fitted winter cover over the pool to help keep out debris and protect it throughout the off-season.
5. Add closing chemicals if needed: Depending on your pool and water conditions, you may choose to add pool-closing chemicals to help maintain water quality through winter.

How to Winterize an Intex Pool

How you winterize an Intex pool depends on the specific model. Some seasonal pools require you to drain, disassemble, and store them, while other models follow different winterization requirements.

Follow your model’s instructions for the pool, pump, filter, and hoses. If the manufacturer recommends seasonal storage, thoroughly drain, clean, and dry everything before you store it for winter.

How to Winterize a Saltwater Pool

Saltwater pools follow many of the same winterization steps as in-ground or above-ground pools. The main difference is that the salt chlorine generator and salt cell require additional preparation before freezing weather.

Remove and Clean the Salt Cell

Inspect the salt cell for scale or buildup and clean it according to the manufacturer’s instructions. If the manufacturer recommends removal, disconnect, clean, dry, and store the cell as directed for the off-season.

Saltwater Chemical Balancing Differences

Test the salt level and other water chemistry before closing, using the recommended ranges for your specific salt system. Don’t add salt simply for winterization unless the manufacturer recommends it. Shut down and winterize the salt chlorine generator according to its instructions, then follow the appropriate in-ground or above-ground closing steps.

Do Saltwater Pools Need Antifreeze?

Saltwater pools may still need pool antifreeze to protect plumbing, depending on the pool and winterization method. Salt in the water does not prevent plumbing or equipment from freezing, so proper winterization is still necessary during an Illinois winter.

Common Winterization Mistakes (and How to Avoid Them)

Avoid these common mistakes to help protect your pool throughout an Illinois winter:

• Closing too early: Warmer water can encourage algae growth after you cover the pool. Base your closing time on water temperature and weather conditions, not a fixed date.
• Improperly winterizing plumbing: Water left in lines can freeze, expand, and damage pipes or fittings. If you’re unsure how to clear your in-ground pool’s plumbing, consider professional help.
• Ignoring chemical timing: Follow product directions for the proper order and timing of closing chemicals. Some treatments need time to circulate before you add the next product.
• Using the wrong antifreeze: Only use antifreeze designed specifically for swimming pools. Never substitute automotive antifreeze in pool plumbing.
• Failing to winterize equipment: Drain and protect pumps, filters, heaters, and other equipment according to manufacturer instructions to prevent freeze damage.
• Ignoring the winter cover: Check your cover periodically for water, debris, damage, and other maintenance needs throughout the winter.

DIY vs. Professional Pool Winterization

DIY Pool Winterization

If you know your pool and equipment well, you may be comfortable handling some or all of the winterization yourself. However, in-ground plumbing, pumps, filters, heaters, and salt systems can make closing more complex, especially when equipment needs protection from freezing.

Professional Pool Winterization

Professional pool closing offers added convenience and expertise while helping ensure important winterization steps aren’t overlooked.

Frequently Asked Questions

When Should I Winterize My Pool in Illinois?

Winterize your pool before freezing weather arrives but avoid closing while the water is still too warm, which can encourage algae growth. Focus on water temperature and weather conditions, not a fixed date.

Do I Have to Drain My Inground Pool for Winter?

Yes and no. Inground pools generally shouldn’t be completely drained for winter because improper draining can damage the liner or structure.

What Chemicals Do I Need to Close a Pool for Winter?

Common pool closing chemicals include products to balance pH and alkalinity, pool shock, and winter algaecide when appropriate. The exact products and amounts depend on your pool’s water chemistry, size, and product instructions.

How Do You Winterize a Swimming Pool?

To winterize a swimming pool, clean and balance the water, add appropriate closing chemicals, protect plumbing and equipment from freezing, and secure the pool with a winter cover. Specific steps vary for in-ground, above-ground, and saltwater pools.

Can I Winterize My Pool Myself?

Yes, if you’re comfortable with your pool’s equipment and winterization requirements. For more complex plumbing, heaters, filters, or salt systems, professional pool closing can simplify the process and help ensure you don’t miss important steps.