How To Winterize A Pool: Complete Step-by-Step Closing Guide

Properly winterizing a swimming pool is one of the most important maintenance jobs of the year in climates where freezing temperatures occur.

A good pool closing protects much more than the water itself. It can help protect:

• Pumps
• Filters
• Heaters
• Salt systems
• Valves
• Skimmers
• Return lines
• Underground plumbing
• Pool surfaces
• The winter cover

The goal is simple:

Leave the pool clean, balanced, protected from freezing, and ready for a much easier opening in the spring.

Do You Actually Need to Winterize Your Pool?

Not every pool needs a full seasonal shutdown.

If you live in an area where temperatures regularly reach freezing or below, a full winterization is commonly necessary.

If you live in a mild climate, you may instead operate the pool throughout the winter or perform only a partial seasonal closing.

That distinction matters because the procedures can be very different.

Full Winterization

A full closing usually involves:

• Stopping normal pool operation
• Removing water from vulnerable plumbing
• Draining equipment
• Installing winter plugs or protection devices
• Covering the pool for the season

Partial Winter Operation

In milder climates, the pool may remain full and circulating while you:

• Reduce operating schedules
• Continue water testing
• Maintain sanitizer
• Use freeze protection
• Remove unnecessary equipment

When Should You Close the Pool?

Do not wait until the first hard freeze is already happening.

Plan the closing early enough that:

• The water can be cleaned properly
• The chemistry can be balanced
• The equipment can be serviced
• The plumbing can be winterized correctly
• You are not rushing during freezing weather

At the same time, closing too early while the water remains very warm can increase the chance of algae growth beneath the cover.

The ideal timing depends on climate, water temperature, equipment, and how you operate the pool.

1. Inspect the Pool Before Closing

Start by taking a walk around the entire pool and equipment area.

Look for:

• Leaks
• Cracked fittings
• Loose plumbing
• Damaged skimmers
• Broken return fittings
• Damaged drain covers
• Unusual pump noises
• Filter problems
• Heater leaks
• Cover damage

Winterizing does not repair existing problems.

In many cases, it is better to address a leak or damaged fitting before freezing weather arrives rather than discovering the problem during spring startup.

2. Clean the Pool Thoroughly

Do not close a dirty pool and assume the winter chemicals will take care of it.

Before closing:

• Skim the surface
• Remove leaves
• Vacuum the floor
• Brush the walls
• Brush steps and benches
• Clean around ladders and fittings
• Empty skimmer baskets
• Remove accumulated debris

Organic debris left in the water can contribute to:

• Algae growth
• Staining
• Sanitizer demand
• Poor spring water quality

The cleaner the pool is when the cover goes on, the easier your spring opening is likely to be.

3. Clean the Waterline

Before lowering the water or installing the cover, clean the pool's waterline.

Remove:

• Body oils
• Sunscreen
• Dirt
• Scale
• Organic residue

Use a cleaner approved for your particular pool surface.

4. Test and Balance the Water

Water chemistry should be balanced before the pool is closed.

At minimum, check:

• pH
• Total alkalinity
• Sanitizer
• Calcium hardness where applicable

Depending on the pool, you may also need to consider:

• Cyanuric acid
• Salt level
• Metals
• Scale potential

The appropriate target values depend on the pool surface, sanitizer system, equipment, and chemical products being used.

5. Shock or Oxidize the Water If Appropriate

Many pool-closing procedures include shocking or oxidizing the pool before the cover is installed.

The purpose is to reduce contaminants and help leave the water in better condition for the off-season.

Follow the instructions for:

• Your sanitizer system
• The specific shock product
• The winterizing products you plan to use

Do not mix pool chemicals together or combine incompatible products.

6. Add Winterizing Products Only as Needed

Depending on your climate and water conditions, a pool-closing program may include:

• Algaecide
• Stain and scale control
• Enzyme products
• Winter sanitizer products

These products can be helpful, but they are not substitutes for:

• Proper cleaning
• Balanced water
• Correct plumbing winterization
• A good pool cover

7. Remove Pool Accessories

Remove equipment that should not remain in the pool over winter.

This can include:

• Ladders
• Handrails where appropriate
• Pool toys
• Floating accessories
• Basketball or volleyball equipment
• Automatic pool cleaners
• Robotic cleaners
• Removable fountains
• Solar covers

Clean and dry the items before storage.

8. Clean and Store Your Pool Cleaner Properly

If you use a robotic or pressure-side pool cleaner, do not simply pull it out and throw it into the garage while it is dirty and wet.

Clean it according to the manufacturer's instructions and inspect:

• Filter bags or cartridges
• Tracks
• Wheels
• Brushes
• Cables
• Hoses

Store it in a dry location according to the manufacturer's recommendations.

9. Decide Whether the Pool Water Level Should Be Lowered

This is one of the most misunderstood steps in pool winterization.

Not every pool should be lowered to the same level.

The correct water level depends on:

• Pool construction
• Vinyl liner vs. concrete or fiberglass
• Type of winter cover
• Skimmer protection method
• Return fitting configuration
• Climate
• Whether the pool is being fully or partially closed

Some winterization procedures lower the water below selected fittings.

Others protect the skimmer and plumbing without dramatically lowering the pool.

Some safety covers also rely on the pool maintaining an appropriate water level beneath them.

10. Protect the Skimmer

In freezing climates, the skimmer needs special attention because water trapped inside it can freeze and expand.

Depending on the winterization system, protection may involve:

• Lowering the water appropriately
• Blowing out the suction line
• Installing a winter plug
• Using a skimmer expansion device
• Following the manufacturer's closing procedure

A common skimmer protection device is designed to absorb some expansion if water freezes inside the skimmer.

11. Blow Out the Plumbing Lines

In climates where plumbing can freeze, removing water from the pool lines is one of the most important parts of the closing process.

Lines that may require winterization include:

• Skimmer lines
• Main drain lines
• Return lines
• Cleaner lines
• Water-feature lines
• Spa plumbing

Pool professionals typically use appropriate air equipment to force water from the lines before sealing or plugging them.

12. Be Careful When Using Compressed Air

Blowing out pool plumbing is not the same as casually blowing air through a garden hose.

Excessive pressure can damage:

• Pipes
• Fittings
• Filter components
• Valves
• Equipment

If you are not familiar with winterizing pool plumbing, this is one part of the closing process worth having performed by an experienced pool professional.

13. Use Only Pool-Safe Antifreeze When Appropriate

Some winterization procedures use antifreeze in plumbing that cannot be completely cleared.

If antifreeze is used, it should be a product specifically approved for swimming-pool plumbing, typically based on non-toxic propylene glycol.

14. Install Winter Plugs Where Required

Once plumbing lines have been properly cleared, winter plugs may be installed in:

• Return fittings
• Skimmers
• Cleaner ports
• Other winterized plumbing connections

Use the correct plug type and size for the fitting.

15. Winterize the Pool Pump

The pool pump must be protected from freezing water.

Depending on the pump and installation, winterization may involve:

• Turning off electrical power
• Removing pump drain plugs
• Draining the pump housing
• Draining connected piping
• Cleaning the pump basket
• Protecting the motor from weather

Follow the pump manufacturer's winterization instructions.

Do not allow the pump housing to remain full of water in a freezing environment.

16. Do Not Seal the Pump Motor in Plastic

It may seem logical to tightly wrap outdoor equipment in plastic, but doing so can trap moisture and condensation.

Some equipment manufacturers specifically warn against wrapping pump motors tightly in plastic because condensation can promote corrosion.

Use appropriate weather protection while allowing ventilation where required.

17. Winterize the Filter

The correct procedure depends on filter type.

Sand Filters

Winterization may include:

• Backwashing
• Draining the filter
• Removing the drain cap
• Placing the valve in the appropriate winter position

Cartridge Filters

Typical steps may include:

• Opening the filter
• Removing cartridges
• Cleaning the cartridges
• Draining the housing
• Inspecting the tank and O-ring

D.E. Filters

These may require:

• Backwashing
• Opening the filter
• Cleaning the grids or elements
• Draining the tank

Always follow the specific filter manufacturer's instructions.

18. Respect Filter Pressure Hazards

Pool filters are pressure vessels.

Before opening a filter:

• Shut the pump off
• Turn off power where appropriate
• Relieve internal pressure
• Confirm the pressure gauge reads zero

19. Winterize the Pool Heater

Pool heaters can contain heat exchangers and plumbing passages that may be damaged if water freezes inside them.

Winterization varies significantly among:

• Gas heaters
• Electric heaters
• Heat pumps

Depending on the heater, winterization may require:

• Turning off power
• Shutting off gas where required
• Removing drain plugs
• Disconnecting unions
• Draining the heat exchanger
• Blowing out plumbing

Use the manufacturer's procedure for your exact heater model.

20. Winterize Salt Chlorine Equipment

If your pool has a salt chlorine generator, check the manufacturer's winter instructions.

Depending on the system and climate, you may need to:

• Remove the salt cell
• Drain the cell
• Install a winter bypass or dummy cell
• Clean the cell if appropriate
• Store components safely

Do not assume the salt system automatically protects itself from freezing.

21. Winterize Water Features

Remember any additional plumbing connected to the pool.

This can include:

• Waterfalls
• Deck jets
• Fountains
• Slides
• Outdoor showers
• Attached spas
• Booster pumps

Each water-filled line exposed to freezing temperatures represents a potential freeze-damage point.

22. Winterize an Attached Spa Carefully

A pool with an attached spa can be more complicated than a pool alone.

The system may contain:

• Shared plumbing
• Dedicated spa returns
• Air lines
• Jet plumbing
• Blowers
• Check valves
• Separate drains

If you do not understand the plumbing arrangement, use a professional rather than guessing which valves and lines need to be cleared.

23. Remove and Store Drain Plugs Properly

Pump, filter, heater, and other drain plugs are easy to lose.

One practical approach is to place all removed drain plugs in a labeled bag or store them in the pump basket so they are easy to find when reopening the pool.

Do not reinstall drain plugs during a full winter shutdown unless the equipment manufacturer's procedure specifically calls for it.

24. Inspect the Winter Cover Before Installation

Do not wait until closing day to discover that the cover is damaged.

Inspect for:

• Tears
• Holes
• Broken straps
• Damaged anchors
• Seam separation
• Heavy wear

Repair or replace the cover if necessary.

25. Choose the Right Type of Pool Cover

Not all covers serve the same purpose.

Traditional Winter Cover

Primarily designed to protect the pool from:

• Leaves
• Debris
• Sunlight
• Winter weather

Safety Cover

A properly installed safety cover is specifically designed and rated for safety applications.

It may use:

• Anchors
• Straps
• Mesh material
• Solid material

26. Secure the Cover Correctly

Install the cover according to the manufacturer's instructions.

Depending on the type, this may involve:

• Anchors
• Water bags
• Cables
• Winches
• Straps
• Special above-ground pool hardware

A poorly secured cover can:

• Blow loose
• Allow debris into the pool
• Become damaged
• Create a safety hazard

27. Above-Ground Pools Require Their Own Closing Procedure

Do not assume that an above-ground pool should be winterized exactly like an in-ground pool.

Above-ground systems may require special attention to:

• Skimmers
• Return fittings
• Liners
• Filter systems
• Hoses
• Wall pressure
• Winter covers
• Air pillows where recommended

Follow the pool and equipment manufacturers' instructions.

28. Vinyl-Liner Pools Need Special Care

A vinyl liner depends on the surrounding water and structure for support.

Removing too much water can create problems such as:

• Liner movement
• Shrinkage
• Wrinkling
• Floating or shifting

Do not significantly lower or drain a vinyl-liner pool without understanding the consequences for that particular installation.

29. Fiberglass Pools Also Should Not Be Drained Casually

Groundwater pressure can create serious problems if a fiberglass pool is emptied improperly.

In extreme situations, hydrostatic pressure can cause a pool shell to shift or lift.

Winterization normally does not require emptying the pool.

30. Watch the Cover During the Winter

Pool closing is not necessarily a "set it and forget it" process.

Periodically inspect the pool throughout winter.

Look for:

• Standing water on the cover
• Heavy snow
• Accumulated leaves
• Loose straps
• Damaged anchors
• Cover tears
• Unexpected water-level changes

Manage the cover according to its manufacturer's instructions.

31. Watch for Abnormal Water Loss

If the pool level drops considerably during winter, investigate.

A significant unexplained drop could indicate:

• Leak
• Cover pump issue
• Plumbing problem
• Structural issue

Do not automatically refill or ignore it without determining what happened.

What If You Live Somewhere That Only Freezes Occasionally?

This is common in many warmer states.

You may not normally close the pool, but a sudden winter storm can still damage equipment.

If a short freeze is expected, your strategy may involve:

• Keeping water circulating
• Activating automatic freeze protection
• Monitoring the equipment
• Preparing for power outages

Some pool automation systems automatically run the pump when air temperature approaches freezing.

However, freeze protection is not a guarantee against damage, particularly if:

• Power fails
• The pump stops
• A valve is closed
• Some plumbing does not receive circulation

Should You Winterize the Pool Yourself?

Some pool owners successfully close their own pools every year.

Others hire a professional.

A professional closing may be especially worthwhile if:

• You have never winterized the pool before
• The plumbing layout is complicated
• You have an attached spa
• You have numerous water features
• The equipment is below the pool water level
• You are unsure how to blow out the lines
• You have expensive pool equipment
• Your area experiences severe freezes

A cracked underground line or heater can cost far more than a professional pool closing.

Common Pool Winterizing Mistakes

Closing a Dirty Pool

Leaves and debris left in the water can contribute to staining and poor spring water conditions.

Lowering the Water Too Far

Different pool structures and covers require different water levels.

Leaving Water in Equipment

Water trapped in pumps, filters, and heaters can freeze and crack components.

Forgetting a Plumbing Line

Cleaner lines, water features, slides, and spa plumbing are easy to overlook.

Using Automotive Antifreeze

Only pool-safe products should ever be used in pool plumbing.

Wrapping Equipment Tightly in Plastic

This can trap condensation around equipment that needs ventilation.

Assuming a Winter Cover Is a Safety Cover

Only a properly rated and installed safety cover should be treated as one.

Closing Too Early and Ignoring the Pool

Warm water plus months under a cover can create a difficult spring opening if the chemistry was not properly managed.

Complete Pool Winterizing Checklist

• Inspect the pool and equipment.
• Remove leaves and debris.
• Vacuum the pool.
• Brush walls and floor.
• Clean the waterline.
• Test and balance water chemistry.
• Shock or oxidize if appropriate.
• Add winter products if needed.
• Remove ladders and accessories.
• Remove and store pool cleaners.
• Determine the correct winter water level.
• Protect the skimmer.
• Blow out plumbing where required.
• Install winter plugs.
• Use pool-safe antifreeze only when necessary.
• Drain the pump.
• Winterize the filter.
• Winterize the heater.
• Winterize the salt system.
• Winterize water features and spa plumbing.
• Remove and store drain plugs.
• Inspect the winter cover.
• Install and secure the cover.
• Continue checking the pool during winter.

Make Spring Opening Easier

A properly winterized pool should make reopening much less difficult.

When spring arrives, you will generally need to:

• Remove and clean the winter cover
• Remove winter plugs
• Reinstall equipment drain plugs
• Reconnect equipment
• Open valves
• Prime the pool pump
• Restart circulation
• Inspect for leaks
• Test the water
• Rebalance chemistry

Do not start a pool pump dry. Make sure it is properly primed according to the manufacturer's instructions before operation.

The Bottom Line

The most important part of pool winterization is not pouring chemicals into the water.

The real goal is to protect the entire system from months of cold weather.

Think of the process as five major jobs:

Clean the pool + balance the water + protect the plumbing + drain the equipment + secure the cover.

If you are unsure about the plumbing or freeze-protection portion of the closing process, hiring a professional can be money well spent.

This article provides general swimming-pool winterization information. Closing procedures vary by pool construction, climate, plumbing configuration, cover type, and equipment manufacturer. Always follow the specific instructions for your pool, pump, filter, heater, sanitation system, and winter cover. If you are uncertain about winterizing plumbing or pressurized equipment, consult a qualified pool professional.