Closing a pool for winter
Closing an in-ground pool is mostly about water you cannot see: the water sitting inside return lines, the skimmer and the heater. Blow it out, plug behind it and keep the pool from being drained, and winter stops being a threat. Here is the whole process in the order it has to happen.
When to close an in-ground pool
Wait until the water is around 65°F (18°C) or below. Cold water is the entire point: it slows algae and collapses chlorine demand, so the pool can sit for months without help.
In-ground pools tolerate a later close than above ground pools, because the plumbing is protected by being blown out rather than by lowering the water below it.
Step 1: clean and balance the water
Vacuum, brush and skim. Then balance pH, total alkalinity, calcium hardness and sanitizer, and record the numbers.
This is also the moment to deal with staining or scale you have been ignoring. It is far cheaper to fix while the water is still warm enough to work in.
Nothing you add this week means anything until you know how much water it is going into.
Step 2: lower the water level
- Lower the water to below the skimmer and the return fittings — often 4–6 inches, or to whatever your pool's manual specifies.
- In a hard-freeze climate some pools keep the level at the normal mark and rely on blowing out and plugging the lines instead. If your manual specifies a level, follow the manual.
Step 3: blow out and plug the plumbing
Every line that holds water has to be emptied, or the first hard freeze will split it.
- Set up the air. Use a shop vacuum on blow, or a compressor turned right down. High pressure through pool plumbing can blow fittings off the wall, and there is never a reason to use full tank pressure.
- Work through every line. Returns, skimmer line and main drain. A line is done when it stops spitting water and only air comes out.
- Plug as you go. Screw expansion plugs into the returns and the skimmer. For the main drain, air-lock it by closing the valve while air is still escaping, or plug it — whichever your fitting is designed for.
- Add antifreeze where water can pool. A small amount in the skimmer and in any low spot absorbs what blowing out left behind.
Step 4: winterize the equipment
- Pump: drain the housing, remove the drain plugs, and store the plugs somewhere you will find them.
- Filter: drain it, clean or replace the cartridge, and plan an end-of-season deep clean for sand.
- Heater: drain the heat exchanger and store the plugs. Trapped water in a heater is one of the most expensive freezes there is.
- Salt chlorinator: remove the cell, inspect and clean it per the manufacturer, and store it indoors.
- If you leave a cell installed, follow the manufacturer's winter bypass instructions to the letter.
Step 5: choose a cover
The real choice is about light and water, not price.
| Solid cover | Mesh cover | |
|---|---|---|
| Water on top | Collects — you need a cover pump | Drains through on its own |
| Light | Blocked, so less spring algae | Passes through, so more chance of green water |
| Leaf debris | Sits on top and can be pumped off | Rots and settles into the pool |
| Handling | Heavier and harder to move alone | Lighter |
Whichever you choose, secure it evenly and check it after storms. And keep people off it — a cover is not a load-bearing surface.
What you are actually protecting
Everything above comes down to three things: water that is cold and balanced, water that is not trapped anywhere rigid, and a cover that cannot fill up and drag on the structure.
Get those three right and opening in spring is a clean-up. Miss one and it becomes a repair bill.
Mistakes worth avoiding
- Draining the pool to make it clean for winter, which risks floating or cracking the shell.
- Using a compressor at full pressure and blowing a fitting off the wall.
- Using automotive antifreeze.
- Leaving the heater full of water.
- Closing with warm, unbalanced water and hoping the winter chemicals cover it.
- Ignoring the cover until the weight has already bent something.
Closing questions
Can I close a pool myself?
Yes, and most owners do. The two steps that go wrong most often are blowing out the lines and remembering the heater, because neither is visible once it is done.
Do I have to use antifreeze in the lines?
Not always — it depends on how completely you can clear the water out. If you have any doubt about a line, especially the main drain or a line with a low spot, pool-grade propylene glycol is cheap insurance.
Solid cover or mesh cover?
A solid cover blocks light, so you get less spring algae, but it collects water and needs a pump. A mesh cover drains itself and is lighter, but lets light through and lets fine debris into the pool. Neither is wrong; pick the problem you would rather have.
Can I just leave the pool running all winter instead?
In mild climates with freeze protection, some owners do — but that is not closing, it is paying to run a pool through winter. In a hard-freeze climate, close it properly.
How full should the pool be over winter?
Somewhere below the skimmer and returns, unless your manual says otherwise. And never empty — see the warning above about a pool that floats.
Related
- How to winterize an above ground pool
- Pool volume calculator (US gallons and litres)
- Pool maintenance schedule — daily to seasonal
- How to backwash a pool filter
Review status: Seasonal and routine maintenance. Last reviewed 2026-09-13. See the source and review status of every formula →