Closing an inground pool involves more than simply adding a few products and installing a cover. In our climate, the main goal is to prevent water from freezing in the plumbing and equipment. A single improperly blown-out line, poorly drained heat pump, or incorrectly installed plug can lead to a major repair in the spring.

Each installation has its own layout, however: number of return lines, main drain, skimmer, salt system, water heater, heat pump, integrated spa, waterfall, automatic filler, pressure-side cleaner, or safety cover. The proper method must therefore follow the pool’s actual configuration and each manufacturer’s instructions. This guide presents a complete and safe sequence, but it does not replace a technical inspection when the plumbing is complex or unfamiliar.

Piscine Hippocampe assists homeowners in Delson, the South Shore, Montreal, and Montérégie with closing products, advice, and professional winterization. You can use this guide as a preparation checklist or entrust us with the closing so that each circuit is identified, drained, and protected.

The best time is generally when the water remains around 12°C or lower, while still leaving enough time before a sustained freeze to complete the work properly. At this temperature, biological activity slows and the closing treatment remains more stable. Closing too early while the water is still warm increases the risk of finding green water in the spring; waiting for freezing temperatures can damage equipment before the pool is even closed.

Monitor the water temperature rather than just the calendar date. However, book your service several weeks in advance: the weather window is short, and professional closing appointments fill up quickly.

Vacuum, brush the walls, and remove leaves. Have the water tested at a store and correct the balance before adding the closing treatment. Clear, balanced water reduces the risk of deposits, corrosion, stains, and algae during the winter.

Clean the filter according to its type and the manufacturer’s instructions. A sand filter may require backwashing; a cartridge filter must be cleaned and dried if removed; a diatomaceous earth filter requires a procedure specific to its model. Do not add multiple concentrated products in the same place, and never mix chemicals together.

1. Determine the final water level

There is no single height that applies to all pools. The level depends on the vinyl liner or finish, the position of the return fittings and skimmer, the type of plugs, and the winter cover. A floating opaque cover, a locking cover, and a Safety Cover are not managed exactly the same way.

Follow the pool and cover manufacturer’s instructions. Never completely drain a vinyl-liner pool: the weight of the water helps keep the liner in place and supports the structure. With a safety cover, the water level must also remain high enough to support the liner under a significant load.

3. Turn off the power and release the pressure

Stop the pump, switch off the equipment breakers, and prevent accidental re-energization. Open the filter air-relief valve until the pressure gauge reads 0. Then close or position the valves according to the circuit that will be blown out. Take a photo of each configuration to make reopening easier.

4. Blow out the pipes

The principle is to push the water out of each branch with a continuous airflow, then close the branch while the air is still flowing. The precise order varies according to the equipment layout and plumbing. The skimmer, returns, main drain, suction port, pressure-side cleaner, waterfall, or integrated spa must be treated as separate circuits.

1. Connect the blower to the point provided by your installation and start at low pressure with sufficient flow.
2. Expel the water from one branch at a time. Wait for a steady airflow and no apparent water spray.
3. Plug the outlet or close the valve while the air is flowing, using the appropriate plug.
4. For the main drain, create an air lock only if the plumbing and valves allow this method. The lock must be checked to ensure it remains in place.
5. Label each completed branch and note any pipe that did not produce the expected behavior.

5. Use antifreeze as additional protection

A non-toxic antifreeze designed for pools and spas may be added to certain pipes after blowing them out, depending on the label and the configuration. It never replaces complete draining and blowing. Do not use automotive antifreeze: its formulation is not intended for pool water and may pose a hazard.

The volume and addition point depend on the length, diameter, and slope of the pipe. Do not pour a product at random into a system whose layout you do not know.

6. Protect the skimmer

Once the skimmer line has been blown out and plugged, install a device designed to absorb or accommodate ice expansion, such as a Gizzmo or a compatible foam assembly. The goal is to provide expansion space in the skimmer; this device does not eliminate the need to properly protect the line.

7. Draining the pump

With the power off and the pressure released, remove all drain plugs identified in the pump manual. Let the housing and basket drain completely. Clean the basket, lubricate the seal only with a compatible product if the manufacturer recommends it, and store the plugs in the basket so you can find them in the spring.

Protect the motor from the elements without wrapping it airtight in plastic, which would trap moisture. The thermal-protection or freeze-protection mode of a variable-speed pump does not replace winterization when the pool is closed.

9. Closing a saltwater pool

A salt chlorine generator generally stops producing effectively when the water gets cold; for example, Pentair indicates that production stops on certain models at around 11 °C. After switching off the power, remove the cell if the manual requires it, inspect it, rinse light deposits with a hose, and store it in a dry, frost-free place.

Do not automatically perform an acid wash every fall. Excessive chemical cleaning can damage the plate coating. Use it only when stubborn scale is present and according to the manufacturer’s method. A dummy cell can be installed on some systems to close the circuit during winter.

10. Winterize the heat pump or heater

Turn off the circuit breaker, isolate the unit from the circuit, and drain all water from the connections, heat exchanger, and low points according to the manual. A small amount of trapped water may be enough to crack a heat exchanger. On some heat pumps, the inlet and outlet connections must be disconnected for drainage, then reconnected once the unit is empty.

Gently clean a heat pump's coil with a low-pressure hose if necessary; a high-pressure jet can bend the fins. Install a cover only if it is designed for the model and recommended by the manufacturer. Gas heaters also require special attention to the power supply and ventilation: have this part handled by a qualified technician if you are unsure of the procedure.