Why Are Pools So Cold?

Swimming is a lot of fun, especially in the hot summer sun. But, sometimes, your pool is colder than you expect it to be—and an overly cold pool can take the fun out of swimming even on the hottest of days. So, why do pools get so cold?

Pools are so cold because not enough sunlight is shining on them to heat them up or because the outside air temperature is too cold, which makes the heat from the water evaporate. Sometimes, pools can feel colder than they really are because heat starts leaving your body when you are in the water.

This article explains the most common reasons why your pool is cold, even in warm weather. I will also explain how you can heat your pool and include a video to show you ways to heat it, so keep reading to learn more!

Reasons Your Pool Is Cold

Pools can get cold for many reasons, and a lot of them vary depending on where your pool is located and how hot or cold the air temperature is. Let’s discuss a few reasons why your pool may be so cold.

Shade or Enclosures Blocking the Sun

One of the main reasons why pools are too cold is that they are not getting enough sunlight. If you have a backyard with trees or even neighboring buildings blocking sunlight from your pool, then the water will be much colder than if it was in direct sunlight. Even if the outdoor air temperature is warm, sunlight is one of the biggest heating factors of pools. 

Sometimes, outdoor pools have screens above them to protect them from animals and insects. These pools will likely stay cold as they will not get enough sunlight to keep the water warm as these screens will block any sunlight from reaching the water. 

And even if your pool is in direct sunlight, it can take a while for the water to warm up since it heats up more slowly than air. So, your pool will still feel cooler right in the morning when the sun first comes up and is not as hot as later in the day. Then at night, as the sun goes down, the pool will cool down quite quickly as the sun stops shining on it. 

Water Evaporation in Cool Air Temperatures

Another reason your pool is cold is that the water evaporates into the air. Water evaporates all the time, but it happens a lot faster in cooler temperatures.

When air evaporates from your pool, the evaporation takes heat with it. In cooler temperatures, more heat is lost from your pool water when there is more evaporation.

So, the cooler the outside air temperature, the harder it will be to keep your pool warm because there will be more evaporation. The more evaporation there is, the quicker your pool water loses its heat. 

You may not have this problem as much in the warm summer months as the air temperature outside tends to stay high even during the night. This will cause much less evaporation, which will in turn keep your water temperature from dropping too much. 

The Water Feels Colder Than Really It Is

water and air feels different

Sometimes, your pool water is not actually as cold as you might think it is. This happens because the air temperature is very high, which can make the water temperature feel a lot cooler than it is relative to the hot air temperature. 

For example, the pool water may be quite warm, say 85 °F (29 °C), but the air temperature outside the pool is even warmer at 100 °F (37 °C). So, when you go from the hot air to the slightly cooler pool, your body will notice a significant difference, and it will feel cold even though 85 °F (29 °C) is warm for a pool.

Another reason why pool water may feel colder than it is has to do with how water and air conduct heat differently. The science behind this is that air does not take heat away from your body as fast as water does. So, even if the temperature in the air is cooler than in the water, your body in the air will retain its body heat for much longer compared to when you are submerged in water.

How To Warm Up Your Pool

Now that you know why your pool is so cold, you might want to warm it up. There are a few methods you can use to warm up your pool. HOW TO HEAT A POOL: IN-GROUND VS. ABOVE GROUND

Pool Heat Pumps

Get a Pool Heater

You can always control the exact temperature of your pool with a heater. Even when the weather gets cold or the sun is not out, you can use your heater to warm up your pool. And if your pool is not cold, you can simply turn the heater off if the water is warm enough on its own.

This Youtube video from Swim University explains three ways you can heat your pool using pool heaters:

Remove Any Objects Obstructing Sunlight

Of course, this method won’t work if your backyard is surrounded by tall buildings or big trees that you cannot get rid of. But, if you have smaller trees or other removable objects that block the sunlight from reaching your pool, you can move these out of the way so that your pool water gets direct sunlight. This simple fix will warm up your pool significantly on sunny days.

Use a Pool Cover to Prevent Water Evaporation in Cold Temperatures

This trick is especially helpful if you live in an area where temperatures drop significantly during the night. Leaving the pool cover on at night or whenever the temperature drops will keep the water warmer for longer. Just remove the pool cover when you want to swim and the heat should stay in the pool for longer than it would without the cover.

Final Thoughts

Having cold pool water can keep you from enjoying your pool even on the warmest of days. If your pool water is cold, it is likely because there is no direct sunlight getting to your pool or because the pool water is cold relative to the temperature in the air. 


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