How Long Does It Take for a Pool To Heat Up?

warm pool water

No one likes to jump into a cold or chilly pool since their bodies will be shocked by the sudden temperature difference. It’s an experience you can avoid by continually keeping your pool warm, whether by the sun, a heater, or a heat pump.

It takes a pool 24 to 72 hours to heat up by 20 °F (11 °C) when using a heat pump. You can also use a heater or the sun to warm your pool. However, several factors such as air temperature, swimming pool or spa size, water temperatures, and heat loss can impact heating times.

In the rest of this article, I’ll discuss how long it takes to heat a pool, several heating methods, the factors that affect pool heating time, and lastly, touch on the best pool temperatures. So, keep reading to learn more.

Different Ways To Heat Your Pool

Most pool owners have one question they can never really get an accurate answer to – how long does it take to heat a pool?

Unfortunately, it’s one of those questions you don’t have a direct answer to because pool heating time depends on several factors and the heating method used.

However, the bigger the pool, the longer it takes to warn the water. For instance, a heat pump can warm a spa within 45 to 60 minutes, while in-ground or above-ground pools can take a few days to warm up by a difference of 20 °F (11 °C).

So, let’s look at how your heating method will impact how quickly your pool heats up. 

Heating a Pool by the Sun

The sun is a free nature source you can use to warm your pool. It’s the most affordable way compared to using a heater or a heat pump.

Your pool water needs to get direct sunlight to absorb the warmth. Heating your pool through the sun depends mainly on the weather condition because it can only happen on sunny days. However, your pool temperature can increase by 0.7 °F (0.39 °C)per hour under the sun.

The main drawback of this method is evaporation, which can cause a loss of 5 °F (2.78 °C) for every quarter inch of evaporated water. So, to keep the temperature and water levels constant, it is best to use a solar cover to avoid evaporation during the day.

Heating a Pool With a Heater or Heat Pump

If you want the most potent pool heating options, you can use a heater or a heat pump. It will cost thousands of dollars with all things said and done, considering the costs of buying the equipment, setup, and usage. However, you can rest assured that these pool heating methods will provide the required warmth to keep your pool open for weeks.

So, are you going to go with a heater or a heat pump for your pool?

Calculating Required Heating Time When Using a Heater or Heat Pump

First, you must determine the amount of water in gallons and the number of British Thermal Units (BTU) per hour that a heater or heat pump can provide.

Generally, one BTU can raise one pound of pool water temperature by one degree Fahrenheit. Therefore, raising the temperature of one gallon of water (equals 8.34 pounds) by one degree will require 8.34 BTUs.

With that information and the weight of water, you may determine the amount of time it will take to raise the water temperature to the desired degree.

Example: A 150,000 BTU heater can increase a 30,000-gallon pool by 1 degree in 1.67 hours.


30,000 gallon x 8.34 = 250,200 lbs

250,200/150,000 = 1.668 hours

Use this basic formula to determine the efficiency of a heater or a heat pump.

The Verdict: Which Is the Best Way To Heat the Pool Water?

Heating the pool by the sun is free, but it’s slower than both the heater and heat pump options.

Heat pumps draw heat from the surrounding air to warm the pool. Therefore, they don’t function best in temperatures below 50 °F (10 °C). On the other hand, heaters work best even in cooler regions, which explains why they are the most expensive option. 

The best way to heat the pool water is with a heat pump or heater since these devices work quickly to keep your pool’s temperature consistent. However, heaters can cost thousands of dollars, so if you are patient and on a budget, using sunlight to heat your pool might be the best option.

Before purchasing a heat pump or a heater, you should consider your average region temperature. 

Tip: I’d recommend purchasing a heater to heat your pool water since it can work in any climate efficiently. Use a sun cover to keep your pool heated for an extended period.

Factors That Affect Pool Heating Time

Whether you’re heating your pool by the sun or with a heater or a heat pump, several factors can influence the speed at which your pool gets heated up. 

  • Air Temperature. The weather plays a significant role in determining the ambient temperature of your pool. If you’re in a colder region, you can expect the air to be chilly or cold. A heat pump may take longer to heat a pool in a colder climate than a warmer one. Heat pumps use surrounding warm air to heat the pool, so they’re the best for areas with 50 °F (10 °C)  and above temperatures.
  • Starting Water Temperature. If the current and desired water temperature gap is significant, you can expect a longer pool heating time. The lower the starting temperature, the longer it will take to heat the pool.
  • Swimming Pool or Spa Size. The size of a pool affects how long it takes to heat the water. So, it would be best to go for an efficient heater or heat pump with a higher BTU depending on your pool size. For example, small heat pumps can work best for small pools or spas, but they can take forever to warm a large pool, even by one degree.
  • Use of a Solar Cover. A solar cover can reduce heating pool time by reducing heat loss, primarily through evaporation. So, if you want to retain heat in your pool overnight, invest in a good solar cover.

Perfect Pool Temperature

Now that you know how long it takes for pool water to heat up, I believe you should be able to achieve the ideal and sustainable pool temperature. The perfect pool temperature ranges between 78 to 82 °F (25 to 27 °C).

If you are patient and wait for your pool to heat up to this range, you’ll have a great time swimming. However, if you want to maintain that temperature, you’ll need to keep heating your pool and use a solar cover as insulation. 


It takes a long time to heat the pool water using the sun, a heater, or a heat pump, and warming up your pool for at least 3-5 days is recommended, even if you have a heat pump or heater with a high BTU. Once your pool is warm, cover it up with a solar cover to trap the heat. 


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