Should My Pool Main Drain Be Opened Or Closed?

Main Drain

As a pool owner, the valves to adjust your pool settings and circulation can be a bit daunting. The pool main drain is pretty simple to figure out and you shouldn’t fear adjusting it!

Should your pool main drain be opened or closed? Your pool Main Drain should be opened when your pool is in operation and your main drain should be closed during the winter. It’s as simple as that when trying to figure out when to close your pool main drain. The main drain should be open during operation as it circulates the water from the bottom of your pool. 

Let’s dive a bit deeper into this question though to see what some pool experts have to say about this topic. The pool main drain is a bit of a heated debate topic in many pool forums with long-time pool owners having strong opinions on the pool main drain. 

Why should the main drain be open?

The main drain should be open because it provides circulation at the bottom of your pool which is incredibly important to keeping your pool water clean and safe. Skimmers that pool water from the surface of the pool can’t reach the water and sediment at the bottom of your pool. This is where the pool main drain shines as it sucks from the lowest point of your pool the water and small particles that you would like to get into the filter. This may not be a concern for smaller above-ground pools but once you get a larger pool, the main drain is extremely useful and you want to have it open to circulate your water.

Most pool builders will tell you to have your pool main drain open to 100% when operating your pool. This will allow the maximum amount of suction at the bottom of your pool into the main drain. There are some nuances to this depending on how your pool plumbing has been set up as the main drain could keep the skimmers from pulling as much as they could. You can dive into that in our article here about how to use your main drain and skimmers together

When should the Main Drain be closed?

The main drain should be closed during the winter months after you have shut down your pool and blown out your main drain pipes. We will have a tutorial for how to blow out your main drain for the winter, but I’ll discuss briefly why you blow it out and then close the lines. 

Since the main drain is the plumbing that is underneath your above-ground pool or underneath the shell of your inground pool these plumbing pipes are tricky to repair if they bust. Having water inside of them during the winter would cause the water to freeze to the point of breaking your pipe when the water expands. This is why you blow out your pipes and then close the drain to keep any water from getting inside the pipe during winter. 

This is in my opinion the only time you will have your main drain fully closed.

Should the Main Drain be 100% opened at the valve?

Now here is a question that has some debate amongst pool builders and long-time pool homeowners. Should my main drain be fully opened to allow maximum suction? I am going to say yes, it should be 100% open doing its job to circulate the water at the bottom of your pool. I do recognize that some pool plumbing can be very specific to that pool and operating your main drain at 100% open may not be the way to go.

One of the reasons is that when the main drain is open, the skimmers at the top aren’t pulling strong enough to grab debris from the surface of the pool. I believe this is a reasonable complaint although in my preference I would rather just clean the top of my pool with a pool rake to grab large debris. This is because the circulation of the water at the bottom of my pool is more important to me as a pool owner. I am very concerned about keeping all of my water moving and keeping it balanced and safe for swimming. 

Where do I open and Close the Pool’s Main Drain?

Your valve to open and close your main drain will be at the plumbing pad where your pump and filter are located. You’ll need to figure out which pipes are for your skimmers and which one is for your main drain. Hopefully, your pool builder has labeled them, it is worth asking your pool builder to do that during the initial setup so you can adjust all of the valves to your liking. If they aren’t labeled, then dig back into your paperwork and you should be able to find some schematics that will give help you determine which valve goes to which pipe. So once you have determined which valve is for the main drain, you’ll want to adjust the valve on the main drain to an open or closed position depending on what you are doing. You can also adjust it to be partially open as well to toy with the performance which we will talk about in the next section. 

Can I adjust the main drain valve?

You absolutely can adjust your main drain valve and I recommend that you try this out. You have made a smart and awesome decision to purchase a pool. If you went the route of getting the main drain in your above-ground pool, I applaud you and think that it will be money well spent. So, since you have made this investment, let’s test out the pull of water into your main drain to find out what works best for your pool. You might open the Main Drain to 20% open and find that this works best for the balance of your pool water and the pull you receive from your skimmers up top. If that works for you, then great! You will have your pool for a long time so it’s best to find out which setup at your valves is the best configuration so that you can be running your pool optimally for as long as possible.

There are forums online where I have seen pool owners who have multiple pools that run every year without the main drain. Now, I have never personally run my pool without using my main drain because I want that circulation but it should be noted that as a pool owner, you shouldn’t be too nervous about “breaking” or ruining your pool water when you adjust the valve. You will still be getting circulation from your skimmers. I make this note because I believe you should dive into your pool plumbing as soon as you can so you can feel comfortable with the whole setup. This will help with troubleshooting issues you might have years down the road. 

Can I operate my Pool if the Main Drain is closed?

Yes, 100% you can still operate your pool if the main drain is closed. As mentioned above, the main drain is for circulation but every pool will have skimmers that provide that circulation as well. There are many many above-ground pools in operation every year that chose not to get the main drain in their pool. I personally don’t recommend it because of the reasons I’ve mentioned above in this article about main drains and if you need one. If your main drain isn’t working for some reason, you can close the main drain and keep operating your pool using only your skimmers for circulation. I do not believe this should be a long-term solution for pool owners but some disagree with me. With that being said, if you need to operate your pool with the main drain valve closed, it is perfectly fine, and go right ahead.


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