How Long Does It Take To Heat a Pool?

How long does it take to heat a pool? Every pool owner has asked themselves that question at one point or another. After all, the whole point of a pool is comfort and fun. Nobody wants to come over and wait around for a pool to warm up. You, and your guests, want to feel warm and comfortable from the moment you jump into the pool. You’ll soon find out how to predict how long it’ll take to heat your pool. In doing so you’ll also discover how to get the most out of it.

How Long To Heat a Pool?

An average sized pool (rectangular 16×36) will take 6 hours to heat 10 degrees with a standard heater (300k BTU). The volume of water to heat, how many degrees it needs to increase and the size of your heater all play major factors in the time needed to heat your pool.

To work the exact time needed there is an equation you can use:

First, determine the weight of the water in your pool by multiplying the number of gallons by 8.34.
Next, find out how many hours it would take to increase the water temperature by one degree Fahrenheit by dividing the weight of the water by the BTU size of your heater.
Finally, decide how many degrees you want to raise the water temperature and multiply that by the time it takes to increase it by one degree to calculate the total time needed to reach your desired temperature.

Note: Using a pool cover greatly improves efficiency and the above equation does not factor that in. In fact often it is cheaper to buy a pool cover than paying more for a bigger heater.

Overviews and Estimates

Without bothering with the equation the simple answer is that it’ll generally take between twelve and forty-eight hours to heat a swimming pool to a comfortable temperature.

Saying that this is a rather large window is an understatement. At the low end, this suggests you might be able to start heating your pool in the morning and enjoy a nice swim in the late afternoon sun. And on the other extreme, you might need to wait two full days before your pool is heated to a comfortable temperature.

Why is there so much variation in this timeframe? There are 3 main factors that determine how much energy and therefore time it takes to heat water:

• The specific heat of the water
• The total mass of the water
• The amount of temperature change needed (i.e how warm you want it from what it is now).

Those are for the basic principle of heating water but with a pool there are a number of variables that influence how quickly your pool will heat up. To get a solid idea of how long it’ll take to heat your pool you’ll need to consider all of the following factors.

The Initial State of the Water

If you’ve ever cooked a huge pot of soup then you know that the original water temperature plays a big part in the speed of getting it hot, starting off with warm water rather than cold water speeds things up tremendously. And the same principle applies to heating up your pool. Consider a situation where you’re able to heat your pool by five degrees every hour. If you only needed to heat the water up by ten more degrees then you’d be finished pretty quickly. But if you started out with extremely cold water then the heating time would take far longer and a lot more energy to finish the process.

Heating Systems

Heaters are one of the single biggest factors to consider when you’re determining how long it’ll take to heat up your pool. There are a lot of different types of pool heaters on the market. Most people are familiar with the standard heat pump systems. But there are a lot of other innovative options on the market. The size and efficiency of your pool heater are usually the main factors to consider when calculating the overall duration of the process.

Some types of heaters, such as electric resistance heaters, can be fairly expensive. This makes it especially important to consider which heating option you want to go with when first looking into swimming pool loans. This is an important consideration if you live in a colder climate where the heating system needs to work harder than it would in a warmer area.

Local Climate

Most people remember being told not to leave the front door open during their youth. “We’re not paying to heat the outdoors” is a common sentiment from parents all over the world. But the concept takes on a different form when you’re heating up your pool. Because you’re quite literally trying to heat the outdoors. And the local climate is going to either help or hinder those efforts.

The overall weather will be a huge factor in how long it takes to heat your pool. Hot summer days where the air temperature is higher will often ensure your pool stays heated without any real need for an internal heating system. Some people take this idea even further with eco friendly pool heating.

Just running the heaters during specific hours can often let you work in harmony with the free heat from the sun.

And some people have taken this even further by using solar pool heaters to keep the pool heated at night with electricity created from the sun during the day.

Pool Surroundings

When people go over pool design ideas they’ll generally focus on the pool’s physical structure. But take a step back and consider the most beautiful pools you’ve ever seen. The design of the pool is important. But how that design fits into its surroundings is equally significant. And this principle holds true for heating as well.

Consider some of the structures around your pool that might limit the amount of sunlight shining down on it. The shade from buildings and trees can make a big impact over time. For example, trees might only block direct sunlight for a few hours, but a few hours when the sun is most intense can still make a big impact on how fast your pool heats up.

You’ll generally see your pool warming faster if you can maximize the amount of sunlight shining down on it.

The type of pool you have also affects the pool temperature, an inground pool has the benefit of being insulated by the earth whereas an above ground pool has the pool walls exposed to the outside air and therefore suffers more heat loss. This is more of a factor during the colder months when the air temperature is constantly trying to bring down the water temperature but does need to be considered when thinking about heating time and energy needed.

Pool Covers

Pool covers are a great way to keep your water free of debris when not in use. But they’re also a great way to heat loss in your pool. This might not seem to make much sense at first. After all, the cover’s blocking the heating potential of the sun. But pool covers are also preventing evaporation. Pool water often evaporates at a surprisingly fast pace. In fact, in the summer you can lose about a full inch of pool water per day if it’s continually exposed to open air and sunlight.

On top of that, the additional use a pool receives during the summer will typically displace a lot of water. All of these causes and more will cause your pool to lose water during the hottest days. And replacing the water instantly disrupts the pool’s temperature. By keeping evaporation from occurring through the use of pool covers you’re also helping to stabilize the pool’s temperature.

Pool Size and Depth

The size and depth of the pool also play an important role in temperature management. You can look at pool heating from a different angle to see why. You’re not really heating a pool, but the contents of a pool. The larger the amount of water in a pool the more heat is needed to bring it up to a comfortable temperature. Or, reconsider the earlier example of cooking soup.

You can bring a small amount of water to the boiling point on a stove fairly quickly. But a huge pot of water is going to take a lot longer to heat up. The same is true of a pool. The more gallons of water in a pool, the longer it’ll take to reach a comfortable temperature. It’s generally best to scale heating systems to the size of your pool. You can get away with a less powerful heating system if your pool is relatively small. But a larger pool will require larger heat sources.

Bringing It All Together

How long does it take to heat a pool? You’ve seen that the generalized answer is twelve to forty-eight hours. And every aspect of pool heating will influence how your pool fits into that prediction. The more optimized your pool heating, the faster it’ll heat up. If you have a smaller pool, great heaters, and use a pool cover then your pool will heat up fairly quickly. But if you don’t, you can always work on adding any of these features.