Pool Winterization: A Step-by-Step Closing Guide

Updated April 2026 · By the SplashCalcs Team

Properly winterizing your pool protects tens of thousands of dollars in equipment, plumbing, and pool surface from freeze damage while ensuring an easy, algae-free opening in spring. A pool that is closed incorrectly can suffer cracked pipes, damaged pumps, stained surfaces, and severe algae blooms that cost hundreds or thousands of dollars to remedy. This step-by-step guide walks you through the complete winterization process so your pool survives the cold months unscathed.

When to Close and Pre-Closing Preparation

Close your pool when sustained daytime temperatures consistently fall below 65 degrees Fahrenheit. Closing too early while water is still warm encourages algae growth under the cover. Closing too late risks freeze damage to equipment and plumbing. In most northern climates, the ideal closing window is late September through October. Southern pools that experience occasional freezes should at least protect equipment even if not fully closed.

One week before closing, begin preparation by running the pool normally and bringing all chemistry into ideal ranges. Superchlorinate (shock) the pool to 10 to 15 ppm free chlorine. Add a winter algaecide per manufacturer dosing. Balance pH to 7.2 to 7.6, alkalinity to 80 to 120 ppm, and calcium hardness to 200 to 400 ppm. Clean the pool thoroughly by brushing walls and floor, vacuuming all debris, and cleaning the filter.

Close when temps consistently below 65F
Shock to 10 to 15 ppm free chlorine one week before closing
Balance pH (7.2 to 7.6), alkalinity (80 to 120), calcium (200 to 400)
Add winter algaecide per product instructions
Thoroughly brush, vacuum, and clean the pool
Clean or backwash the filter

Pro tip: Do not close your pool before water temperature drops below 65 degrees consistently. Warm water under a cover creates ideal conditions for algae that will bloom without any sanitizer, resulting in a green mess at opening.

Lowering Water Level and Blowing Lines

Lower the water level 4 to 6 inches below the skimmer for mesh covers or 12 to 18 inches below the tile line for solid covers. For pools with a cover pump, the lower level is not as critical. Never drain a pool completely for winter, as groundwater pressure can pop a fiberglass shell out of the ground or crack a gunite shell.

Blowing water out of plumbing lines is the most critical winterization step. Using a shop vacuum or air compressor, force air through each plumbing line until water stops coming out at the other end. Plug each return fitting and skimmer with expansion plugs after blowing. Any water left in pipes can freeze, expand, and crack the pipe, causing costly underground repairs in spring.

Lower water 4 to 6 inches below skimmer for mesh covers
Blow all plumbing lines with compressed air until clear
Plug returns and skimmer with winterizing expansion plugs
Never fully drain the pool, groundwater can cause structural damage
Add non-toxic antifreeze to lines as additional freeze protection

Pro tip: After blowing lines, add a gallon of non-toxic pool antifreeze to each line through the skimmer and returns as extra insurance. This provides protection against any residual water that the blowing process missed.

Equipment Winterization

All pool equipment must be drained and protected from freezing. Remove all drain plugs from the pump, filter, heater, and chlorinator. Store drain plugs in the pump basket so they are easy to find in spring. For DE and sand filters, set the multiport valve to the winterize position or between positions so water cannot be trapped. Remove the pressure gauge and store it indoors.

Disconnect and store chemical feeders and salt chlorine generators indoors. Remove salt cells and clean them with a mild acid solution before storage. If your pump is not protected from the elements, consider wrapping it with insulation or a pump cover. Shut off the circuit breakers for all pool equipment to prevent accidental activation during winter.

Remove all drain plugs from pump, filter, heater, chlorinator
Store drain plugs in pump basket for easy spring location
Clean and store salt chlorine generator cell indoors
Set filter valve to winterize position
Turn off all pool circuit breakers
Cover or insulate exposed equipment

Pro tip: Take a photo of your equipment pad showing all connections and valve positions before closing. This makes spring opening much easier, especially if a different person opens the pool.

Pool Cover Installation

A properly installed pool cover prevents debris from entering the pool, blocks sunlight that fuels algae growth, and provides safety if rated for that purpose. Solid covers block all light and debris but require a cover pump to remove rain and snowmelt. Mesh covers allow water to pass through while blocking debris and do not require a pump but may allow fine particles into the pool.

Safety covers anchored to the deck with spring-loaded straps cost $1,200 to $3,000 and are the gold standard for winterization. They support the weight of a child or pet that might wander onto the cover. Standard winter covers held down by water bags cost $100 to $300 but provide no safety benefit and can sag into the pool. Regardless of cover type, ensure it is secured tightly with no gaps where wind can catch underneath.

Safety cover: $1,200 to $3,000, anchored to deck, supports weight
Solid standard cover: $100 to $200, requires water bags and cover pump
Mesh standard cover: $150 to $300, no pump needed, allows water through
Cover pump for solid covers: $50 to $150, prevents water accumulation
Ensure cover is tight with no gaps for wind

Pro tip: If using a solid cover, place the cover pump in the center and run its drainage hose off the deck. Check the pump after every rain or snowmelt event. Water accumulation on a solid cover can become heavy enough to collapse the cover into the pool.

Spring Opening Preparation

A well-winterized pool makes spring opening straightforward. Remove the cover carefully, cleaning debris off the top before pulling it off the pool. Clean the cover, let it dry completely, and store it folded in a dry location. Reinstall all drain plugs, reconnect equipment, and reassemble the salt cell and chemical feeders. Fill the pool to normal operating level before starting the pump.

After starting the pump and filter, test the water chemistry comprehensively. Even a well-winterized pool will need adjustment after months of dormancy. Shock the pool to break down any organic matter that accumulated over winter. Run the pump continuously for 24 to 48 hours after opening to circulate and filter the water thoroughly. Bring a water sample to your local pool store for a full analysis if you are unsure about balancing.

Remove cover, clean, dry, and store properly
Reinstall all drain plugs and equipment connections
Fill pool to normal level before starting pump
Test and adjust all chemistry parameters
Shock pool and run pump 24 to 48 hours continuously
Bring water sample to pool store for comprehensive analysis

Pro tip: Open your pool when water temperatures approach 60 degrees rather than waiting until warm weather. Opening early prevents algae from getting a head start in warming water under the cover, making the opening process much cleaner and faster.

Frequently Asked Questions

When should I close my pool for winter?

Close when sustained daytime temperatures drop consistently below 65 degrees Fahrenheit. In most northern regions, this is late September through October. Closing too early while water is warm encourages algae growth under the cover.

Can I leave water in my pool over winter?

Yes, you should leave water in the pool. Never drain a pool completely for winter. The weight of the water stabilizes the pool structure against groundwater pressure. Draining a fiberglass pool can cause it to pop out of the ground, and draining a gunite pool can cause cracking.

Do I need a cover pump for my pool cover?

Yes, if you use a solid winter cover. Rain and snowmelt accumulate on solid covers and can become heavy enough to collapse the cover into the pool. Mesh covers allow water to pass through and do not need a cover pump.

What happens if I do not winterize my pool?

Failure to winterize risks freeze damage to plumbing lines (cracked pipes cost $500 to $3,000 to repair), damaged pump and filter components, stained pool surfaces from unbalanced water, and severe algae blooms that can cost $200 to $500 in chemicals to clear.