Should I Drain My Pool For The Winter?
Asking "Should I drain my pool for the winter?" seems like an innocent enough question, however as a pool and spa expert a question like this is not a terribly good sign. The answer to this question about whether you should drain your pool or not is a resounding "No!" and the reason why I am so concerned about a question like this is that you are asking a yes or no question...but if you choose the wrong answer then your pool will likely be destroyed over the winter season.
Never, never, NEVER, drain your swimming pool!
Never includes winter. In fact, the winter is possibly the most important time to make sure that you have water in your pool. Now, to get technical, there are MANY different kinds of swimming pools, located in MANY different kinds of climates. The geography of the pool, combined with the unique construction style used for your specific pool, will determine how to maintain it, including how to prepare for a winter season. The swimming pool industry is dynamic in nature, and the technical information about how to care for a concrete pool in Vancouver Canada will not likely apply very well to a vinyl liner pool located in New Jersey USA, nor one located in Florida. There are many different pool construction styles as well, and each of them has unique care and maintenance instructions, and performing the wrong maintenance on your pool can be costly to say the least. What is also significant are the environmental factors such as the water table surrounding the pool, the soil conditions, the amount of rain and/or snow, the extremes of temperature that the pool will potentially be exposed to...the list goes on and on.
Of course the reality is that you can drain a swimming pool. Or more accurately, I can. Sometimes. With certain pools. Under specific conditions. Do you see how many qualifying statements you need to add about when it is OK to drain a pool? This is why it is better to be safe than sorry and simply apply the blanket statement - NEVER drain your pool. Now, with that said, let's talk about specifics behind the different kinds of pools and the potential risks associated with draining them for the winter.
Draining An Above Ground Pool For The Winter
Before we can talk about why you should not drain an above ground pool for the winter you should first familiarize yourself with some of the different types of aboveground pools. Temporary pools are not meant to withstand freezing off season temperatures. These entry level swimming pools are the only type of pool which you can drain and pack away for the winter. Aboveground pools that have a vinyl liner are what I would consider to be the entry level pool into the "professional quality" category, so this is where we will start.
An aboveground pool with a vinyl liner should not be drained, but for a different reason than inground vinyl liner pools. Usually, aboveground pools do not have a shallow end and a deep end - most are flat bottom. Even those with floor contours will usually only have a "dished hopper" (a pool sloped to the deepest point in the middle) or a coved section where the wall meets the floor. Without a deep end to pull the liner away from the shallow end, most likely you could drain an above ground pool and the liner would not shift much. Much. Once a vinyl liner has been exposed to UV from the sun, as well as chemicals such as chlorine, it will shrink slightly and lose elasticity. This is why you can not re-purpose an old pool liner. Once used, if you let the liner dry out it will become stiff and brittle. Very old liners shatter like glass when you let them dry out. The older the liner is, the less plasticizers will remain in the material.
When you drain an above ground pool the liner will shrink, shift, and ultimately never go back to as good as it once was - even if you refill with water right away after draining. It would be common to expect to see wrinkles in the liner if you did drain and refill your above ground pool. Even if you are thinking that you need a new liner anyway, what you might not realize is that the weight of the water on the floor helps to protect it. You do not want to leave your pool empty for the winter even if you need a new liner as this will result in, at minimum, extra work that needs to be done to the floor when it comes time to hang a new liner in the pool. It is also worth noting that there are many different styles of aboveground pool kit. Some of these styles rely on the weight of the water pushing out on the walls to help structurally support the pool kit. A pool like this left empty for the winter would very likely suffer structural stresses and failures to the wall components.
Draining An Inground Vinyl Liner Pool For The Winter
If you have an inground vinyl liner swimming pool, then you have a minimum safe water level that you must observe at all times. You must keep at minimum a few inches of water (usually six to 12 inches is safe) covering the floor of the shallow end of the pool at all times. Due to the mechanics of how a vinyl liner is installed into an inground pool, this water level represents the normal safe level beyond which you can expect to damage your liner if you drain past this point. Inground vinyl liner pools almost all have a shallow end and a deep end. When the liner is first installed it is manipulated manually into position by the installers while under suction from liner installation vacuums. These vacuums hold the liner precisely where it needs to be until such time as the water level in the pool rises enough to hold the liner where it should be. Once there are a few inches of water covering the shallow end floor it is typically safe to remove the liner vacuums and allow the weight of the water to set the liner the rest of the way as the pool fills.
As soon as there is no water weight on the shallow end floor of the pool, the weight of the water in the deep end hopper will start to pull your liner away from the shallow end walls towards the deep end of the pool. This will cause stretching to the liner in any place where it is held firmly in place by a flange and gasket - such as a return fitting, or a flange around a set of in-wall steps. In these areas the liner is being pulled away but can not move. The resulting stress either stretches, distorts, weakens or tears the vinyl in these areas if there is not enough elasticity in the liner to handle the pull. If you drain an inground vinyl liner pool past the shallow end, more times than not this will require a new liner to repair.
Too many pool owners incorrectly assume that they need a new liner anyway, so just drain the pool for the winter and deal with it in the spring. This would be a costly mistake to make. Just as with an aboveground vinyl pool, but even more important, the vinyl liner and water weight in the pool actually serve to strengthen and protect the overall shape and structure. This is one of the reasons why "draining your pool for us" made the top list of things you should NEVER say to your pool guy. Even if you need a new liner anyway in the spring, do not drain your vinyl pool for the winter. Without the water covering the floor it is very likely that you would require additional floor repairs, all the way up to a complete new smooth bottom which might cost as much as $3000 or more depending on where you are located. Additionally, a vinyl pool kit should have outward pressure on the walls from the weight of the water. Leaving a vinyl pool empty for an extended period of time, especially in cold climate areas, significantly reduces the strength of the pool to resist structural failures like shifting or bowing walls, or collapsing of the slopes in the pool. If these things happen to your pool you essentially need an entirely new pool installation and it is going to be costly for sure.
Draining A Concrete Pool For The Winter
Draining a concrete pool for the winter is a bad idea. Unfortunately there are enough people who drain theirs "successfully" as to spread misinformation to other concrete pool owners as to what is OK, and not OK to do to your pool. Can you drain a concrete pool for the winter? Maybe. Should you drain a concrete pool for the winter? No, probably not. Concrete pools are strong, and heavy, and typically built durable enough to last 30, 50, 70 or more years in serviceable condition. If you drain yours, it is entirely possible that spring will come and you can fill it up and everything will be fine. In fact, some concrete pool owners do this every year, and it always works out just fine. Still that does not mean that you are supposed to drain a concrete pool for the winter.
What you can get away with doing, and what is a good idea, are two totally different things. The problem with draining a concrete pool for the winter is that IF the wrong set of circumstances arises it can result in your entire pool being destroyed. A concrete pool is, or at least is supposed to be, hydrostatically balanced in the ground. Just like a rubber ducky in the bathtub, when you push it under water and let go the ducky shoots right up out of the water and floats on top. But if you were to replace the air inside the rubber ducky with water it would be totally different. More or less the ducky would become neutrally buoyant in the water. When you fill a concrete pool with water, the water in the pool opposes the forces from the water outside of the pool. It becomes neutrally buoyant in the ground. Even with a small amount of force from ground water trying to lift the pool, a concrete pool will not move because it is extremely heavy itself. Still, given the wrong set of circumstances such as a blocked hydrostatic relief valve in the main drain, or unusually heavy rains or flash flood conditions, a concrete pool can be exposed to a much greater lifting force than it can oppose. The shell then will either crack to relieve the pressure, or will lift out of the ground.
Obviously a concrete pool that has popped out of the ground is a worst case scenario. It is worthwhile to consider that even if you have no ground water or "popping pool" concerns in your area, the interior surface of a concrete pool should still be kept wet to protect it against the elements. Again, there are many different ways to build a concrete pool, and as such each will have unique considerations. All concrete pools require an interior surface of some kind, whether this be pool plaster, or a proprietary masonry or pebble interior surface, or epoxy, or paint or even tile. The interior surface of a concrete pool is the single most expensive maintenance cost for owning a concrete pool and so logic would dictate that you want to get the longest possible service life from yours. No matter what kind of interior surface you have in your concrete pool, it is designed to be used underwater. Many of these interior surfaces will fail if you allow them to completely dry out. Some fail as they delaminate from the substrate concrete shell due to a different rate of expansion and contraction under temperature variations like direct sunlight. If you live in an area with freeze and thaw conditions then leaving your pool empty for the winter will almost certainly cause damage to the interior surface. You are better off to winterize the pool, but leave water in the pool to protect it. Yes, there is concern for the water line freezing and causing damage...but this is the nature of the beast in cold climate areas. Better to have only the top of the waterline freeze as opposed to exposing the entire interior surface of the pool to freeze and thaw conditions for an entire winter season.
Draining A Fiberglass Pool For The Winter
OK - slow your roll buddy. How did you ever get the idea that you could drain a fiberglass pool for the winter? Regardless of where you live, and the climate that your pool is exposed to, it would probably be a very bad idea to drain your fiberglass pool for any period of time...let alone an entire winter! Fiberglass pools need to be neutrally balanced within the ground, just like concrete pools, to oppose the force of ground water that pushes up on the pool in the ground. However, unlike concrete pools, fiberglass pools do not weigh tens of thousands of pounds when they are empty. Fiberglass pools are also not as strong as concrete pools against bowing, shifting, twisting or pretty much any other force application.
It is worth noting that fiberglass is actually stronger than concrete, or even steel, based on equal thickness. Concrete pools however are up to a foot thick, or more, and this is much more overall strength than the much thinner, albeit stronger, fiberglass pools. Fiberglass pools are the easiest of all pool styles to install, but they are also the weakest to opposing environmental conditions. If you add to these environmental conditions by draining your fiberglass pool, you can pretty much count on experiencing a total failure of the pool. A fiberglass pool can pop out of the ground just the same as a concrete pool, but they also experience problems with twisting, bowing and cracking quite often - much more so than a concrete pool would. Usually when you drain a fiberglass pool you would be actively controlling the ground water surrounding the pool for the entirety of the time the pool is empty. This would include pulling the hydrostatic relief valves and continually pumping the water that fills into the pool from beneath. Under normal conditions you would only drain a fiberglass pool for needed service, and you would control the site conditions the entire time, with the goal being to refill the pool as quickly as possible. If you own a fiberglass pool you should absolutely never drain it on your own, and leaving it empty for the winter would almost certainly break it.
Learning How To Winterize Your Pool
If you are asking whether you should drain your pool for the winter or not then chances are there are other questions that you still have about how to get your pool ready for cold weather (or extended periods of inactivity). Now that you know a little more about how, and why, you should not drain your pool, you should take a look at these articles that build on this information:
How To Winterize A Pool Heater
8 Part Video Series On Pool Winterizing
Opening Your Pool After Being Closed For The Winter
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