If you're tired of jumping into a freezing pool, getting an 18x36 solar cover might be the smartest move you make this season. There's nothing quite like that mid-July feeling when you're ready for a swim, only to dip your toe in and realize the water feels like an ice bath. It's a total mood killer. But honestly, most of us don't want to spend a fortune on gas or electric heaters just to make the water bearable. That's where these giant sheets of bubble wrap—officially known as solar covers—come into play.
Why the 18x36 Size is Such a Standard
If you have an 18x36 pool, you probably already know it's one of the most common sizes for rectangular inground pools. It's a great size for laps and family games, but it's also a lot of surface area to lose heat from. When you buy an 18x36 solar cover, you're essentially getting a lid for your pool.
One thing I always tell people is that even if your pool is slightly smaller or has a weird step-out section, you should still go with the 18x36. It's incredibly easy to trim these things down with a pair of household scissors. You just lay it on the water, let it settle for a day so the packing creases flatten out, and then snip around the edges. It's much better to have a little too much material than to have gaps where heat can escape.
How These Things Actually Work
It's not magic, though it kind of feels like it when you peel the cover back on a sunny afternoon. An 18x36 solar cover works on two fronts. First, it acts as a magnifying glass. Those little bubbles are designed to trap the sun's thermal energy and transfer it directly into the water. On a bright day, it can raise your pool temperature by 10 to 15 degrees over a week or so.
The second part—and this is actually the more important part—is evaporation. Did you know that most of the heat loss in a pool happens because of evaporation? It's true. When water turns into vapor, it takes a massive amount of heat with it. By laying a cover over the surface, you're stopping about 95% of that evaporation. It's like putting a lid on a pot of coffee; it stays hot way longer than if you left it open to the air.
Choosing the Right Thickness (Mil)
When you start shopping for an 18x36 solar cover, you're going to see a lot of talk about "mil." No, that's not millimeters; it's a measurement of thickness. Usually, you'll see 8 mil, 12 mil, and 16 mil options.
- 8 Mil: These are the lightweights. They're much easier to handle and fold up, but they don't hold heat as well and they tend to fall apart faster. If you're on a tight budget or you don't have a reel, this might be the way to go.
- 12 Mil: This is generally considered the "sweet spot." It's heavy enough to provide excellent heat retention but isn't so heavy that you'll throw your back out trying to move it.
- 16 Mil: These are the heavy-duty beasts. They're thick, they're durable, and they hold heat like a champ. However, they are a literal workout to move manually. If you go with a 16 mil cover for an 18x36 pool, I'd say a reel is almost mandatory.
Clear vs. Blue: Does the Color Matter?
This is a classic debate in the pool world. Most 18x36 solar cover options come in either a standard blue or a clear/translucent style.
The blue covers are great because they look "pooley" and they do a decent job of holding heat in overnight. However, clear covers are actually better at letting the UV rays penetrate deeper into the water during the day. If your main goal is to heat the water up quickly, go clear. If you just want to maintain the temperature you already have and you like the look of blue, stick with the classic. Honestly, the difference isn't so massive that you'll regret picking one over the other, so don't lose sleep over it.
The Reality of Handling a Large Cover
Let's be real for a second: an 18x36 solar cover is a huge piece of plastic. When it's wet, it's heavy and awkward. If you're planning on folding this by hand every time you want to swim, you're probably going to stop using it after two weeks. It's just the way it goes.
If you have the space and the budget, get a reel. A reel allows one person to roll the cover up in about thirty seconds. Without one, you're looking at a two-person job of folding it like a giant, soggy bedsheet. Plus, folding it on the concrete deck tends to scrape the bubbles and shorten the life of the cover. A reel keeps it clean and off the ground.
Maintenance and Longevity
I wish I could tell you that an 18x36 solar cover will last forever, but it won't. The combination of intense UV rays and pool chemicals (especially chlorine) is basically designed to eat plastic. On average, you can expect to get about 2 to 3 years out of a decent cover.
To make it last as long as possible, you've got to be careful with your chemistry. If you just "shocked" the pool, do not put the cover on. That super-high chlorine level will make the bubbles brittle and they'll start flaking off into your filter. Wait until the chlorine levels drop back down to the normal range before covering it up.
Also, when you take the cover off and leave it on the reel, use a white protective sheet to cover it. If you leave the rolled-up cover sitting in the direct sun, the layers can actually melt together or "cook" because the heat gets trapped inside the roll. It sounds crazy, but it happens all the time.
Saving Money on Chemicals and Water
One of the perks of using an 18x36 solar cover that people often overlook is the savings. Because the water isn't evaporating, your chemicals stay in the pool longer. Chlorine is expensive these days! When the sun hits an uncovered pool, it eats up your free chlorine pretty fast. The cover acts as a shield, keeping your water balanced for a longer period.
And then there's the water bill. Filling up an 18x36 pool is no joke. If you live in a dry climate, you could be losing thousands of gallons a month to the air. Keeping it covered when you're not using it is just common sense for your wallet.
Is It Worth the Hassle?
At the end of the day, a pool is a big investment, and you want to actually use it. If the water is 72 degrees, you're probably not going to stay in for long. If an 18x36 solar cover can get that water up to a comfortable 82 or 84 degrees, it suddenly becomes the favorite spot in the house.
Sure, it's a bit of a pain to roll out and roll up, and it's not the most beautiful thing to look at when it's on the water. But for the sake of an extra two months of swimming season (one at the start and one at the end), it's hard to argue with the results. It's arguably the most cost-effective way to heat a pool, period. If you're on the fence, just go for it—your toes will thank you the next time you decide to take a dip.