How to winterize and close an in-ground swimming pool

Frozen swimming pool in Dallas

Here are the steps to winterize a swimming pool. The method described below whereby pool plumbing pipes are blown out and sealed first was most widely performed in New England and the East coast of the US. It is now becoming common to perform this method throughout the US and in other countries.

A slight variation of these steps can be performed where the pool is partially drained and an anti-freeze product is added to the lines instead of blowing out the lines and sealing them. Some of the trade-offs with that slightly different method are discussed below when that step is outlined.

NOTE: A swimming pool winterization of this type is rarely done in Texas or some of the other southern states because the weather typically does not stay below freezing for enough days to freeze the ground to a depth where there are benefits from blowing out the lines or having anti-freeze in them. We have a separate post about how most pool owners commonly deal with how to winterize a swimming pool in Texas.

How to winterize and close an in-ground swimming pool.

  1. Gather supplies
    First try and find any chemicals and supplies used from previous years such as the cover, cover weights, skimmer plugs (also called gizmos sometimes) antifreeze, and floatation devices for a cover. For a full winterization you will also typically want to use an air compressor to blow out your swimming pool lines.

  2. Filter preparation 
    If you have a sand or DE filter it is important that you start by backwashing it.  Then pull the filter plug to drain the main tank. You will also want to pull open the backwash valve and leave it open if it is a “push-pull” or slide style backwash valve. If you have a “dial” or multiport backwash valve it is generally not a good idea to remove the top and expose the spider gasket to ice buildup – however it is recommended to make sure it does not have water in it.

    Sand filters should also have the main drain plug removed and water drained out. It is important to get air inside the filter. If you have a small filter that can be drained and carried into a warm area where it will not freeze this is preferred. If you are taking a DE or cartridge filter inside, this is an opportune time to clean the cartridges or DE grids beforehand. If you use Acid on the DE grids be sure to fully rinse them so the acid does not continue to corrode the grids when in storage.

    You can also unthread the filter unions that connect it to the plumbing pipes to further drain water from the filter and backwash valve.

    NOTE: Many swimming pool companies put the drain plugs for all the equipment items in the pump basket.
     
  3. Blow out the lines at the pool equipment 
    Use your air compressor or a shop vacuum to blow out the lines if possible and plug them. This is a two person job. 
     
  4. Pump preparation 
    Disconnect the drain plugs on your pump and put them in the pump basket. If your pump has unions you can completely disconnect it from the plumbing and turn it up-side down to get any remaining water out of it.
     
  5. Heater preparation
    Pull the drain plugs on the front and back “headers”. Not all heaters have multiple drain plugs. If you have an air compressor try to blow any remaining water out of the heater. It is generally not recommended to remove a heat exchanger or burner tray. 
     
  6. Additional equipment
    If you have any additional equipment like an in-line chlorinator, booster pump, auxillary pumps or valves with drain plugs it is helpful to apply the same steps outlined above to these. Unscrew and loosen any quick disconnect fittings or unions at your pump and filter system.  
     
  7. Return jets and skimmers
    Remove any return jet fittings. Also remove the skimmer baskets and weirs (weirs are the little flappers at the throat of a skimmer that function as a door). 
     
  8. Blow out return lines
    Use an air compressor to blow out all the return jet pipes. Make sure to keep the air blowing until the air is visible coming back into the jets of the pool.  Put a plug in the fitting under the water when you see the bubbles blowing at full force. Doing this right can get over 95% of the water out of the return lines. 

    NOTE: There are some companies who recommend draining the water down below the skimmer throats. There are some potential trade-offs here in doing this but you will not have air bubbles coming out if the water is below the return lines.
     
  9. Blow out suction lines
    Also use and air compressor to blow out all the return lines. Use a Gizzmo-style screw to plug the skimmer when bubbles are visible. Be very careful to get the Gizzmo-style screws installed properly. Put PTFE tape on the Gizzmo threads before installing to ensure a tight seal.

    You can also use black rubber-type plugs instead. They will work if there is something in the skimmer to allow for water expansion when it freezes. Usually a closed plastic empty soda-type bottle will work. It is crucial that you have those bottles in place to avoid cracking your skimmers. 

    If you have a slide, an auto vac system or a waterfall, you will have to drain and blow out those suction and return pipes as well. 

    NOTE: Suction and return lines that are properly blown out do not require anti-freeze type products in the pipes.  Anti-freeze type products can be a lot of work to clean up in the Spring so it is preferable to avoid using them if possible.

    Blow out main drain suction line. No pool diving is needed. When you see bubbles coming out of the drain simply close the main drain valve to create an air lock.

    Additional line preparation: Cover or cap any exposed pipes at the equipment. Remove dive board and ladders. Put them in a safe spot such as a shed or the garage along with the pool pump and filter.
     
  10. Chemistry preparation 
    Pre-dissolve any shock or granular based winterizing chemical products one at a time in a bucket before adding them to your pool water. If any granules are undissolved make sure to brush them till they are fully absorbed into the water. If you have a pool liner this is extra important as residual chemicals can bleach or damage a liner. Make sure the chlorine is over 3ppm.

    Test the pool for pH and Total Alkalinity.  Adjust to normal levels using pH PLUS or MINUS and ALKALINITY PLUS.  pH should be between 7.2 - 7.6 and Alkalinity between 80-120 ppm. 
     
  11. Water level
    There are differing opinions on this topic. In the New England area many pool owners do not drain any water out of the pool. This works if all the lines have been effectively blown out and sealed as described. If a pool has ceramic tiles it is recommended to drain the water a few inches below them, but not further.

    Some pool owners swear by having their pool drained down past the skimmer. This is usually done instead of blowing out the pipes and using gizzmos.

    Here are some trade-offs:

    • Pools that are drained cause a lot of undue stress on the pool cover shortening its life by exposing the pool liner to the air. The additional air exposure will cause it to prematurely dry out.
    • Pools that are drained are also at risk of any water buildup on top causing the cover to eventually fall in.
    • Also if a swimming pool is partially drained you have to remove or "lower" the pool light. 
       
  12. Install the pool cover
    Inspect the cover before installing. When inspecting the cover, if you find and rips or tears try to patch or repair them ahead of time. A swimming pool patch tape or heavy duty duct tape can be used to patch lightweight covers. A vinyl pool patch will be needed for vinyl covers. Place the cover on the pool. 

    If you are using water tubes place them through loops on cover. Fill tubes with water till they are ~ 85% full. When water tubes freeze you do not want the water in them to expand and split the tubes. Lay the tubes out end to end no more than 1 foot apart. Any leaking tubes must be replaced.
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