How to Winterize Your Swimming Pool

It’s a sad day when you have to decide to close your pool for the winter. But, winterizing your pool is an inevitable process for most pool owners in the USA. Not only will it protect your pool over the cold winter months, but it will also prolong the life span of the pool in general. If you have an indoor pool with a temperature-controlled environment or live in a temperate region that doesn’t get too cold, there’s no need to winterize your pool.

On the other hand, you do need to winterize things if you have an outdoor pool in colder climates where freezing temperatures are typical during the winter months. Here’s what you should know about this process.

Why It’s Important To Winterize Your Pool

Winterizing a pool is essential for avoiding a wide variety of problems. Here are the most common threats winter poses to your pool.

Cracked Sides

Water expands when it freezes. So when the water freezes in a pool, that pressure could put cracks in the pool’s surface itself. These cracks can be difficult and expensive to repair, so preventing this is one of the main goals of winterizing a pool. Fortunately, this usually isn’t a threat if the water is low enough, and we’ll discuss that in more detail below.

Burst Pipes

When water freezes inside the pipes, it can break and burst them. Burst pipes are challenging to locate and usually even harder to repair than cracks in the pool, so it is recommended to empty the pipes before plugging them up for the winter.

Personal Safety

Although converting a swimming pool into an ice-skating rink may sound appealing on paper, it can pose a serious risk to personal safety if not done correctly. The exposed ice may not be thick enough for movement, so anybody who walks or skates across a frozen pool may end up falling in.

Chemistry Troubles

Cold and freezing temperatures can affect your pool chemistry. The cold temperatures usually stop the growth of algae and bacteria, but improperly winterizing your pool could throw off the chemical balance and eventually lead to structural damage.

When To Winterize Your Pool

Winterize your pool before temperatures drop below freezing in your area. Unfortunately, cold snaps can be unpredictable. You may not always have the opportunity to winterize the pool properly before it gets too cold outside.

In these cases, the best option is to keep your pump running and winterize your pool as soon as possible. The water won’t freeze if you leave the pump on, so it might seem like a good idea to leave it on all winter, but this could still cause problems if there’s a power outage. Therefore, it’s better to winterize when you can. If you’re experiencing frigid temperatures, you can also add antifreeze to your lines.

If There Are A Lot Of Trees Around

If trees surround your pool, winterize and cover it before the leaves start falling in. Otherwise, it will be a lot of extra work for you to get all the leaves out of the pool before you start winterizing it.

How to Winterize An Inground Pool: Step-by-Step Process

Make sure you have the following to winterize your inground pool:

  • Pool testing kit
  • Winterizing chemical kit
  • Plastic dam
  • Air compressor
  • Gizzmo
  • Pool cover

Once you have the above in hand, follow these steps for winterizing your inground pool.

Step 1: Thoroughly Clean Your Pool

Remove all debris from the surface, the bottom, and the sides of your pool. Read the instructions for your automatic pool cleaner, as many manufacturers recommend taking them out of the pool before temperatures drop. In this case, you may need to clean your pool manually.

Be thorough while cleaning. Any organic material left in the pool could stain it, so the primary goal of this step is to get the entire pool as clean as possible.

This cleaning process also includes the filter. If you have a cartridge filter, take the cartridge out, clean it, and put it back in place. You should also clean sand filters and DE filters before winterization.

Step 2: Check Your Pool Chemistry

The next step for winterizing your pool is checking the pool chemistry. In particular, look at your pH, overall alkalinity, and calcium hardness. If these are all within the appropriate ranges for your pool, you’re ready to start winterizing. If they’re incorrect, adjust them.

Some people shock their pool before winterizing. If you haven’t done that in a while, do it before checking and adjusting the rest of your pool chemistry.

Step 3: Add A Winterizing Chemical Kit

Many pool stores sell winterizing chemical kits that should last for the entire season. Use one of these in your pool and follow the manufacturer’s directions exactly.

Never mix chemicals or cleaners unless instructed to do so. Pool chemicals are generally safe when used as directed, but combining them incorrectly could be dangerous or deadly. This precaution also holds if you’re using household cleaners in or around your pool.

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Step 4: Let The Pool Chemicals Filter

It’s tempting to continue winterizing right away, but for most pools, patience is key. Let all of your pool chemicals cycle and filter through the pool for 24 hours. Doing so ensures that your chemicals obtain maximum coverage, thereby giving your pool maximum protection over the winter months.

Step 5: Lower The Water Level

After the chemicals have circulated, lower your pool’s water level. For most pools, this means reducing it below the mouth of the skimmer and return lines. Fiberglass pool water levels shouldn’t go that low, but lowering the water below the skimmer for other pools will protect them once your water starts freezing.

Some pools can benefit from plastic dams that go in front of skimmers to keep water out. These can also hold up covers like tarps and liners, so consider using them even if you’re just lowering your water level.

Make sure not to lower the water too much. Doing this can result in hydrostatic pressure, which can cause severe damage to pools over time.

Step 6: Drain And Store The Pump And Filter

Remove the plugs from the pump and filter. And allow all of the water to drain entirely out of your pump and filter system. This includes any pool heaters or other equipment you may be using. Leaving too much water in the pipes will damage the equipment in the winter, so get as much water out as possible. Once all of the water has been removed from your pool equipment I highly recommend storing them for the season.

Step 7: Empty And Seal The Return Lines

After you have removed and safely stored your pool equipment it is time to clear the return lines.  If you do not clear the return lines when winterizing your pool you risk damaging the plumbing of your pool, which can be very expensive to fix. The best way to ensure all of the water is out of the return lines is to use an air compressor to blow the water out.

Once the water in the return lines is removed plug each return line with a freeze resistant pool plug.

Step 8:  Add a Gizzmo to your Skimmer

Once you have plugged the return lines you should add a Gizzmo to your skimmer. Gizzmos are specialized tools that protect your skimmer system by absorbing the expansion of freezing water.  The Gizzmo is simple to install and will protect your pool from below freezing temperatures.

Step 9: Take Everything Out

Remove any handrails, ladders, or other components and equipment that are still in the pool.

Step 10: Cover Your Pool

Finally, cover your pool with an appropriate pool cover. Many people use options like vinyl covers or tarps. I’d recommend a winter pool cover made of thick vinyl material for climates with colder, harsher winters. You may need to place a pump in the middle to remove rainwater that could otherwise weigh the top down. Read my full guide on how to properly cover your pool for more tips.

Here’s a video covering the steps I outlined above.


How to Winterize An Above Ground Pool: Step-by-Step Process

Winterizing an above-ground pool is slightly different from winterizing an inground pool.

Let’s start with a supplies checklist:

  • Pool testing kit
  • Pool chemicals
  • Skimmer plate
  • Air compressor
  • Pool air pillow
  • Pool cover

Step 1: Clean Your Pool As Thoroughly As Possible

Like inground pools, start by cleaning your pool as thoroughly as possible. This process involves clearing the top, scrubbing the walls, and getting everything off the pool floor. The more thorough you are, the better.

Step 2: Adjust The Chemistry

Measure your pool water’s chemistry, then adjust or shock it as needed. Get the water chemistry as close to perfect as possible. When winterizing, it’s better to be on the high end of each chemical range. The chemicals will wear out eventually, but if they’re relatively high to start with, they’ll last longer.

Step 3: Add Algaecide

Adding an algaecide is optional, but usually a good idea.

Step 4: Clear The Lines

Once you’re done adjusting the chemicals, clear your pool lines. This process is usually as easy as disconnecting them, letting the water run out, then air-drying them, and storing them out of direct sunlight. Drying the lines is an especially important step to prevent mold growth.

Step 5: Protect Your Skimmers

It is imperative to protect your skimmer, as freezing water will likely damage the skimmer of your above ground pool. Most above-ground pools work best with a skimmer plate, a solid cover that seals the skimmer away from the pool. Adding one of these means you won’t have to lower the water level either, saving time.

If you don’t want to plug it up, take some water out of the pool, making sure the level is below the skimmer.

Step 6: Protect Your Pump And Filter

For the pump, remove all of the drain plugs and let them drain. Then take out your pool pump, hoses, and any additional components. Store all of the parts in a covered shed or a temperature controlled area for the winter. This way, you won’t have to go hunting for them when spring arrives.

For filters, follow the manufacturer’s directions for winterizing them. Different filters require different care, so there are no universal guidelines for winterizing these.

Step 7: Remove Accessories

Accessories include toys, pool ladders, and anything else you might leave in or around your pool when it’s open. Clean them thoroughly, then store them in a dry area away from sunlight.

Step 8: Install A Pool Pillow

Also known as ice compensators, pool air pillows help balance the weight of any ice and snow that fall on top of your cover. For best results, keep the pad around the middle of the pool.

Only inflate the pillow to about 55% of its maximum capacity. Avoid filling it all of the way, the pillow should have some give to allowing it to compress under the weight of snow without breaking.

Read my guide on what size pool pillow you need to determine what makes sense for your swimming pool.

Step 8: Put Your Cover On

Finally, it’s time to put your safety cover on. Some people use solid covers, while others use tarps or thinner tops. Whatever you want to use is fine as long as it works. Just make sure you don’t weigh it down with anything that could damage your cover, your liner, or the pool itself if it falls in. For example, this means bricks are a terrible choice. Keep the cover clean and dry throughout the winter and remove snow when it accumulates.

If you need any additional materials for completing all the steps above, a typical pool closing kit should have everything you need.

Below is a video covering these steps for above ground pools.


Winterizing a Saltwater Pool

Winterizing a saltwater pool is not much different from winterizing a traditional chlorine pool. You go through the same steps as you would for a chlorine pool by cleaning it, testing and balancing the water, adding winterizing chemicals, and covering the pool. The only extra step with winterizing a saltwater pool is storing the saltwater chlorinator (SWC). Make sure to check the instructions of your specific SWC on how to winterize it. But most will instruct you to remove it, drain it, and store it.

To maintain the quality of the pool as best as you can over the winter, here are some additional tips:

  • Clear the cover of debris
  • Check the water chemistry at least every two months
  • Keep track of the water chemistry and water level
  • Adjust the water chemistry and level as necessary

Winterizing a Pool in Warmer vs. Colder Climates

Winterizing your pool is going to look different depending on where you live. You might live in a warmer state like Texas or California with mild winters, which will require fewer steps when winterizing a pool. When you close the pool in a warmer climate, it is unnecessary to lower the water levels as the water won’t freeze over. However, you should still clean the pool thoroughly and balance the water before covering the pool at the end of the season.

On the other hand, those that live in colder states will have different factors to worry about, such as snow and extreme temperatures that will freeze the pool water. This climate warrants some extra protection for your pool. When water freezes, the water will expand enough to damage your equipment if you aren’t careful with winterizing your pool correctly. Ensure that you lower the water level below the skimmer in colder climates. You should also drain the pump, filter heater, and other pool equipment to prevent them from freezing over.

Frequently Asked Questions

Can I leave my pool full over the winter?

I advise that you keep your pool full over the winter. Although the water freezing over may be concerning, the reality is that the pool will be more prone to cracks and damages without the water in the pool. Water acts as a protective barrier to prevent these cracks to the surface. Leaving the water in the pool is also cheaper and easier as you won’t have to refill it at every start of the season.

What chemicals do you put in a pool for winter?

You need to make sure that all of the chemicals are balanced in the water before you close it for the winter. Depending on what your pool water needs, you’ll want to add the following:

  • Chlorine to shock the pool
  • Muriatic acid to balance the pH and total alkalinity
  • Algaecide to kill algae growth

A lot of pool stores also sell a winterizing pool kit which will include all of the chemicals you need for your pool.

How much shock do you need to winterize your pool?

As a general rule, use around 2 pounds of shock for 10,000 gallons of water. However, read the instructions of the chemical used. Follow the manufacturer’s directions for best results. If you plan to use an algaecide as well, shock your pool a couple of days before you use the algaecide. Otherwise, high chlorine levels will make it ineffective.

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And that’s it! Any questions? Shoot me a note. Also be sure to check out my guides on winter swimming pool maintenance and opening your inground pool once the warmer months roll around.

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