How to Close and Winterize a Pool in Toronto

The calls we dread in April are the ones that start with “the pump won’t prime.” Very often the cause goes back to one rushed afternoon the previous October, when water was left in a line or a pump housing and froze. Ice expands. Plastic fittings, filter tanks and heater exchangers crack. The damage sits hidden under the cover all winter.

So this guide spends most of its time on the steps that prevent freeze damage. If you only want a list to tick off, our pool closing checklist is the short version.

Before closing day

Aim to close once daytime water temperature has settled into the mid-teens Celsius or lower, which in Toronto usually means late September to mid-October. Close while it is still warm and algae has time to grow under the cover. Leave it too late and you are working with cold hands and frozen hoses. Our post on when to close your pool in Toronto goes into timing.

A few days ahead:

• Bring the water into balance (see our pool chemicals guide). Balanced water is far less likely to stain or scale over winter.
• Brush and vacuum thoroughly. Anything left on the floor sits there for six months.
• Clean or backwash the filter.
• Check you have your winter supplies: winterizing chemicals, plugs for the returns and skimmer, a skimmer guard or gizmo, antifreeze rated for pools, and your cover.

Closing day, in order

1. Shock the pool and add algaecide with the pump running, then let it circulate for several hours. Some winter chemical kits are added near the end instead. Follow the kit’s instructions.
2. Remove ladders, rails, steps, slides and the skimmer basket. Store them somewhere dry.
3. Lower the water level. For most in-ground pools with a mesh safety cover, that means below the skimmer mouth and the return fittings. Your cover type and pool design decide exactly how far.
4. Blow out the lines. Using a shop-vac on blow or a dedicated blower, push water out of every suction and return line until you see air bubbling out in the pool, then plug the fitting while air is still flowing. Do the skimmer, the returns, the main drain line if you have one, and any cleaner or water-feature lines.
5. Add pool antifreeze to lines where the manufacturer recommends it, as extra insurance against water you couldn’t fully remove.
6. Drain the equipment. Remove the drain plugs from the pump, filter, heater and chlorinator or salt cell. Leave the plugs out, and keep them in the pump basket so you can find them in spring.
7. Disconnect what can come inside. A salt cell, a small pump or a cartridge can be stored indoors. Turn off power to the pump and heater at the breaker.
8. Install the cover, tensioned evenly, with the anchors and straps checked.

The step that goes wrong

Step 4. Blowing out lines looks simple and is easy to get slightly wrong. If you stop blowing before the plug is seated, water runs back. If one return is plugged before another is cleared, air takes the easy path and you think a line is clear when it isn’t. Heaters are especially unforgiving, because the heat exchanger holds water in places you can’t see.

This is the part of a closing we would most encourage you to hand over if you’re not sure. It is also why our pool closing service in Toronto treats the plumbing as the main job, not the cover.

Above-ground pools

The idea is the same with a few differences. Usually you lower the water less, disconnect the hoses to the skimmer and return, and bring the pump and filter indoors if they are portable. An air pillow under the cover helps take pressure from ice off the walls.

During the winter

Glance at the cover after big storms. On a solid cover, pump off standing water. On any cover, don’t let kids or pets play on it, and don’t chip at ice on it.

Questions we get asked

Do I need to drain my pool for winter?

No. In-ground pools should never be fully drained for winter. Groundwater can push an empty pool or its liner out of position. You lower the level, you don’t empty it.

Can I close my pool before the leaves fall?

You can, and many people do, but warm water under a cover in early fall can grow algae. Closing a little later, or using a cover that blocks light, helps.

What happens if a pipe freezes?

Often nothing shows until you open the pool and find a leak or a pump that won’t prime. Our leak detection team can find underground breaks without digging up the whole yard.