Closing a pool for the season is more than just pulling a cover over the water and walking away. As the temperature begins to drop and the swimming season fades, the focus shifts from recreation to preservation. These same winterization principles apply to commercial pools at gyms, hotels, and community facilities, where equipment rooms and plumbing runs are often more complex.
When winterization is done poorly or ignored, the consequences usually appear in the form of cracked pipes, damaged pump housings, or severely stained liners. Water expands when it freezes, and in a closed system like pool plumbing, that expansion has enough force to rupture heavy duty PVC and metal components. Taking the time to follow a methodical closing routine is the most effective way to avoid these headaches.
Know your cold weather timing and what can freeze
Timing is just as important as the method. You should generally wait to close the pool until the water temperature is consistently below 65 degrees Fahrenheit. Closing too early, while the water is still warm, allows algae to grow even after you have added winterizing chemicals. However, you must also keep an eye on the forecast for the first hard freeze. If a sudden dip in temperature occurs before you have cleared the lines, the standing water in your equipment can freeze and cause immediate damage.
Plumbing complexity also dictates how much effort you need to put into the winterization. A simple pool with one skimmer and one return is easier to manage than a custom setup with multiple suction lines and extra features.
Balance the water before closing
Water chemistry remains active even when the pool is not in use. Before you put the cover on, you must ensure the water is chemically balanced. This is not about making the water comfortable for swimmers, but about protecting the pool surface from corrosion or scaling during the long months of dormancy.
The pH level should be between 7.4 and 7.6, and the total alkalinity should be between 80 and 120 parts per million. If the pH is too low, the water becomes acidic and can etch the plaster or degrade the vinyl liner. If it is too high, you may find stubborn calcium deposits on the tile line when you open the pool in the spring.
Finally, you should add a winterizing shock and an algaecide. These chemicals work together to kill any existing spores and provide a residual defense against organic growth. It is important to let the pump circulate these chemicals for at least 24 hours before you move on to the next step of the process.
Deep clean and prep the system
Leaving organic debris like leaves, acorns, or silt in the pool over the winter is a recipe for disaster. As these materials break down, they consume the sanitizer you just added and leave behind tannins that can permanently stain the pool floor.
Start by skimming the surface and then move on to a thorough brushing of the walls and floor. Vacuuming the entire floor is essential to remove any settled debris. Once the pool is physically clean, you should backwash your sand or DE filter or thoroughly clean your cartridge filter.
Lower the water level and protect the skimmer
Lowering the water level serves two purposes. It moves the water away from the tile line, which can be damaged by ice expansion, and it allows you to clear the plumbing lines more easily. For pools with a solid cover, the water is typically lowered to about six inches below the skimmer. For pools with a mesh safety cover, the water may need to be lowered further, perhaps 12 to 18 inches, because rain and snow will pass through the mesh and raise the water level over time.
While the water is low, you must protect the skimmer. In cold climates, a skimmer can crack if water gets inside and freezes. Many homeowners use a plastic expansion plug, often called a Gizzmo, which screws into the bottom of the skimmer.
Blow out lines and use pool antifreeze correctly
This is the most critical stage of the winterization process. You must remove the water from the underground pipes to prevent them from bursting. Using a high volume air blower, you force air through the plumbing from the equipment pad back toward the pool. You will see bubbles rising from the returns and the skimmer, indicating the water has been displaced. If you want a quick overview of what a professional closing visit typically includes, you can review our Pool Maintenance & Cleaning services.
Once the lines are clear of water, they are sealed with expansion plugs to create an airlock. This prevents water from seeping back into the pipes. In addition to blowing the lines, many technicians use pool antifreeze as a secondary layer of protection. It is vital to use non toxic propylene glycol based antifreeze specifically designed for pools. Never use automotive antifreeze, as it is highly toxic to humans and will damage the pool environment.
Drain and protect the equipment pad
Once the lines are clear and sealed, your attention turns to the equipment pad. Every piece of equipment that holds water must be drained. This includes the pump, the filter tank, the heater, and any chlorinators or salt cells.
Pump and filter
Remove the drain plugs from the pump housing and the bottom of the filter. Place these plugs in the pump strainer basket so you do not lose them over the winter.
Heaters and salt cells
Heaters are particularly sensitive to freeze damage because they have thin walled copper heat exchangers. Ensure all drain valves are open and use air to blow out any remaining water from the heater internal headers.
Covers and securing against wind, snow load, and debris
The cover is the final line of defense. A good cover keeps out sunlight, which prevents algae, and keeps out debris, which prevents stains.
If you use a safety cover, ensure the springs are tensioned correctly so the cover is taut and stable. For solid covers, make sure the edges are properly secured so wind cannot lift and flap the material.
Off season checks
Winterization is not a set it and forget it task. Throughout the winter, you should periodically check the pool, especially after a major storm or a period of heavy rain. Look for cover movement, loose anchors, or water levels rising high enough to reach the skimmer.
Common winterization mistakes that cause freeze damage and spring headaches
One of the most common mistakes is failing to clear the main drain line. Because the main drain is at the bottom of the pool, many people assume it cannot freeze. However, the pipe travels up toward the equipment pad and can freeze near the surface. You must blow air through the main drain until it bubbles, then quickly close the valve at the equipment pad to create an airlock.
Another mistake is forgetting to remove the “eyeball” fittings from the return jets before inserting the winter plugs. If the fitting is left in, the plug might not seat properly, allowing water to leak back into the pipe. Additionally, some homeowners try to save money by using cheap tarps instead of proper pool covers. These often fail under the weight of snow, dumping a winter’s worth of dirty water and debris into the pool.
When to call a professional for winterization and leak prevention
While many homeowners can handle basic winterization, some systems are complex enough to require a professional touch. This is especially true for commercial pools and shared facilities, where multiple pumps, longer plumbing runs, and higher system complexity leave less room for error. If you are unsure about the integrity of your plugs or the sequence of blowing out the lines, reaching out to PSST Pool Service Inc. can ensure the job is done correctly before the first deep freeze. Professionals have the specialized equipment and experience to identify potential weak points in the plumbing that a homeowner might overlook.
Winterization checklist recap
- Wait until water temperature is consistently below 65 degrees Fahrenheit
- Balance chemistry, then circulate for at least 24 hours
- Skim, brush, vacuum, and clean the filter
- Lower the water level based on your cover type
- Protect the skimmer with a Gizzmo or expansion device
- Blow out lines, plug to create an airlock, use pool antifreeze if needed
- Drain pump, filter, heater, and any connected systems
- Secure the cover and recheck after storms during the winter
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