Do You Need a Skimmer Plug When Closing a Pool for Winter?
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A backyard pool should feel like something you can close for the season without worrying about what winter might damage. But one small component can make a surprisingly big difference when temperatures drop: the pool skimmer plug. If you are wondering whether you really need one, the answer depends on your pool's plumbing, winter weather, and closing method. Understanding what a skimmer plug actually protects can help you avoid frozen pipes, cracked skimmer housings, and unpleasant surprises when spring arrives.
The important distinction is that not every pool needs the same type of skimmer protection. A simple pipe plug, a skimmer-mouth winter cover, and an ice-expansion device perform different jobs. Choosing the right combination matters more than simply buying a plug and assuming the skimmer is winter-ready.
Do You Actually Need a Skimmer Plug for Winter?
Quick answer: If your pool experiences freezing temperatures and you are shutting down its circulation system, the skimmer plumbing generally needs to be drained or cleared and protected against water reentering. A properly fitted winterizing plug is a common way to accomplish this. However, a skimmer-mouth closure or another manufacturer-approved winterization system may serve a different protective function. The exact equipment depends on the pool design and closing procedure.
In climates where freezing temperatures are rare, homeowners may operate their pools year-round rather than perform a complete winter closing. Those pools do not necessarily require winterizing skimmer plugs as part of their normal seasonal routine. Still, occasional freezes deserve attention, especially when equipment is exposed or circulation stops during a power outage.
For pools in regions with sustained freezing weather, skipping appropriate skimmer protection can leave water trapped in vulnerable plumbing or inside the skimmer housing.
What Does a Pool Skimmer Plug Actually Do?
A pool skimmer draws surface water into the filtration system. Beneath the skimmer basket, one or more openings connect to plumbing that carries water toward the pump or, in certain designs, connects with another suction passage.
When water freezes, it expands. Water trapped inside a confined pipe or skimmer body can generate enough pressure to damage fittings, split plumbing, or crack the skimmer housing.
A winterizing plug seals an appropriate plumbing opening after the line has been cleared. Its primary purpose is to prevent water from flowing back into the protected pipe.
That protection is different from absorbing ice expansion inside the skimmer itself. A plain rubber plug can close a pipe without providing meaningful space for expanding ice in the surrounding skimmer chamber.
Three Types of Skimmer Protection That Homeowners Confuse
Before purchasing winterizing supplies, identify which component your pool actually needs.
- Threaded or rubber expansion plug: Seals an appropriately sized plumbing opening. It helps keep water out of a winterized line but does not inherently protect the entire skimmer housing from ice expansion.
- Ice-expansion skimmer device: Typically threads into a compatible skimmer port and extends into the skimmer chamber. Its compressible design creates space for expanding ice while also sealing the connection when properly installed.
- Skimmer-mouth winter closure: Fits over the opening between the pool and skimmer, helping prevent pool water from entering the skimmer chamber. Its installation and compatibility depend on the skimmer and pool construction.
These devices are not automatically interchangeable. Some closing methods use more than one protective component, while others rely on a specifically designed closure system.
Why Plugging the Skimmer Is Not Enough by Itself
One of the most common winterizing mistakes is installing a plug while leaving substantial water inside the connected plumbing.
A plug seals an opening. It does not remove the water already trapped behind it.
In freezing climates, skimmer suction lines are commonly cleared using a properly sized pool winterizing blower and then sealed according to the plumbing layout. The correct procedure depends on whether the skimmer has a dedicated suction line, a shared connection, or an equalizer arrangement.
Even after the pipe has been protected, the skimmer chamber can collect rainwater or melting snow. If that water freezes inside an unprotected housing, damage remains possible.
This explains why experienced pool closers often address two separate concerns: keeping water out of winterized plumbing and accommodating ice expansion in the skimmer body.
How to Winterize a Pool Skimmer Properly
The following checklist outlines the general sequence for a conventional pool in a freezing climate. Always follow the pool and equipment manufacturers' instructions, since plumbing configurations and water-level requirements vary.
Skimmer Winterization Checklist
- Turn off the circulation system. Disconnect power as appropriate and make sure the pump cannot start unexpectedly during winterization.
- Set the recommended winter water level. Some pools require lowering the water below the skimmer, while compatible winter closure systems permit different levels. Never assume that every vinyl, fiberglass, or plaster pool should be drained to the same height.
- Remove the skimmer basket. Clean out leaves and debris. Remove the weir door if the manufacturer recommends it.
- Identify each opening. Determine which port connects to the pump and whether another opening serves an equalizer, main-drain connection, or other function.
- Clear the plumbing. Use the appropriate winterization method to remove water from the skimmer line. Avoid uncontrolled high-pressure air, which can damage equipment or create an injury hazard.
- Install the correct winterizing plug. Check thread size, gasket condition, and fit. Seal each applicable opening according to the system's instructions.
- Protect the skimmer housing. Use an approved ice-expansion device, skimmer closure, or other recommended protection where freezing water could enter the chamber.
- Complete the remaining pool closing. Winterize return lines and equipment, address water chemistry, and install the appropriate pool cover.
If your skimmer has multiple ports or the piping arrangement is unclear, do not guess which opening to seal. Blocking the wrong connection can leave another pipe exposed to freezing water.
Does Your Pool Type Change the Answer?
Inground Pools
Inground pools in freezing climates usually need their skimmer suction plumbing winterized and sealed. The skimmer housing may also need an ice-expansion device because water can enter through the mouth or accumulate from precipitation.
Some inground systems have two openings at the bottom of the skimmer, which may connect to different parts of the suction system. Their winterizing requirements are not necessarily identical.
Above-Ground Pools
Above-ground pool skimmers often have a shorter plumbing connection, but exposed pipes and fittings are still vulnerable to freezing.
Some owners use a skimmer-mouth closure that allows the pool to retain more water during winter. However, protecting the opening does not eliminate the need to properly drain or winterize the connected hose and equipment.
Vinyl-Liner and Fiberglass Pools
These pools deserve particular attention when choosing winter water levels. Lowering the water excessively can create liner-support or shell-related problems under certain site conditions.
A compatible skimmer closure may allow an owner to avoid unnecessary draining, but the appropriate closing level must follow the pool builder's guidance and account for groundwater conditions.
Common Skimmer Plug Mistakes That Lead to Winter Damage
Before closing, check for these avoidable problems:
- Using the wrong plug diameter: An undersized expansion plug may leak, while an oversized plug can damage a fitting or fail to seat correctly.
- Overtightening threaded fittings: Excessive force can stress plastic threads or crack an aging skimmer connection.
- Assuming the skimmer lid is watertight: Ordinary lids typically do not prevent rainwater and snowmelt from entering the housing.
- Leaving the skimmer full of water: Sealing the pipe alone does not remove the possibility of ice pressure against the chamber walls.
- Using automotive antifreeze: Conventional automotive antifreeze is inappropriate for pool winterization. Use only antifreeze specifically approved for swimming-pool systems when recommended.
- Ignoring damaged seals: A cracked gasket or distorted closure can allow water to reach plumbing that was previously cleared.
A particularly easy detail to overlook is the condition of the skimmer itself. Hairline cracks near the bottom ports, damaged threads, or a loose faceplate should be addressed before winter rather than hidden beneath a cover.
Can You Close a Pool Without Lowering the Water Below the Skimmer?
Sometimes, yes. Certain properly fitted skimmer-mouth closure systems are designed to isolate the skimmer while the pool water remains relatively high.
This can be useful for pools where retaining water supports the liner or shell, or where draining large amounts of water is undesirable.
However, the closure must be compatible with the specific skimmer opening and installed according to its instructions. A poorly seated closure can admit water during winter, particularly as water levels fluctuate.
Keeping the pool level high also does not mean the pump, suction line, or other plumbing can be left full of water in freezing conditions.
What If Your Pool Has Been Losing Water Before Winter Closing?
Unexplained water loss deserves investigation before a pool is closed. A declining level might reflect evaporation, a plumbing leak, a skimmer problem, or another opening in the pool structure.
If the pool is still operating and weather conditions permit testing, the Mini Bucket Test offers a simple first step for comparing evaporation with possible leak-related water loss. It does not identify the leak location or establish a definitive diagnosis, but it may help determine whether additional investigation is worthwhile.
Keep in mind that a water-loss comparison cannot establish whether a skimmer winterizing plug seals correctly. Suspected skimmer cracks, leaking connections, or damaged fittings require direct inspection and sometimes professional testing.
When Should You Ask a Pool Professional to Handle the Skimmer?
Professional winterization is particularly worthwhile when the pool has complex suction plumbing, combined spa connections, an unfamiliar skimmer design, or a history of freeze-related repairs.
It is also sensible if you cannot confidently identify the skimmer ports, properly clear the line, or determine the correct winter water level.
For homeowners who experience repeated skimmer cracking despite using winter plugs, the underlying problem may be inadequate ice-expansion protection, water entering the chamber, a poor plumbing seal, or an incorrectly installed component. Replacing the same plug every year may not solve the issue.
How Do You Know the Skimmer Is Ready for Winter?
Before installing the final cover, verify that the skimmer plumbing has been properly cleared and sealed, the protective device fits securely, and any required ice-expansion protection is in place.
Check the condition of accessible fittings and confirm that the selected pool water level follows the manufacturer's closing guidance.
After major winter storms, inspect the pool and cover from a safe location when conditions allow. Unexpected water accumulation or a displaced skimmer closure may warrant attention from a pool professional. Never walk on an icy or snow-covered pool cover to reach the skimmer.
The Bottom Line: Protect the Pipe and the Skimmer
Do you need a skimmer plug when closing a pool for winter? For a conventional pool being shut down in a freezing climate, a properly sealed skimmer line is normally an essential part of winterization. A suitable skimmer plug is one common way to achieve that protection, but it is not the only component that may be required.
The safest approach is to understand your skimmer design, clear the plumbing correctly, choose compatible winter protection, and account for water that could freeze inside the skimmer chamber. A little attention to these details during closing can prevent a much more complicated pool opening in spring.