When Is the Best Time to Heat Your Pool? Day or Night?

Summer always goes by too quickly. In the colder months to follow, you wistfully glance at your pool and dream of the warmer season. A pool heater allows you to keep your pool open longer, potentially all year. When heating your pool, is it better to do it during the day or at night?

Heating a pool in the daytime is the most cost-efficient. Daytime maximizes the use of the Sun’s natural heat and means the pool heater doesn’t need to work as hard or run for as long to heat the water.  If you swim in the early morning, heating the pool during the night will be a better option, as the pool will take several hours to warm up.

If you have more questions about heating your pool, we have the answers. Ahead, we’ll talk about the ideal time to heat your pool, the advantages of doing so, and how you can control pool heating costs. Make sure you keep reading!

Sunrise over the pool
Sunrise over the pool

When’s the Best Time to Heat a Pool?

Keeping your pool’s heater running 24/7 is inadvisable for two reasons. Firstly, the cost two keep a pool heater running constantly is high. The second reason not to keep your pool heater running 24/7 is the additional wear and tear you’ll put your heater through. So for optimal savings, you must decide to heat your pool during the day or at night.

The best time to heat your pool is during the day.

This goes back to what we touched upon in the intro. Even during a cold winter’s day, the daytime temperature is going to be anywhere from 10 to 20 degrees warmer than it is at night, sometimes even warmer.

That warmer ambient air will mean the pool heater won’t need to work as hard. Additionally, if you use a heat pump or solar heating, the warm ambient air will make either heating system much more effective.   

Only heating your swimming pool during the day requires a bit of pre-planning though. For example, if you know you want to swim in the afternoon, then you should turn your heater on in the morning as it will take several hours to heat your water. How long it takes to heat up depends on a number of factors such as the ambient air temperature, if you have a pool cover, the water temperature, the pool’s construction materials and several other things.

This schedule gives the pool adequate time to warm up so you can use it. You can then turn the pool heater off when you’re done using the pool for the day.

Should You Run Your Pool Heater At Night?

Okay, but what if you want to swim first thing in the morning? That brings us to overnight usage of the pool heater.

In many instances, heating the pool at night is not recommended. The dark, wet, warm conditions of your pool can encourage algal growth, which is one more headache to have to deal with.

However, going back to the situation we introduced in the paragraphs above where you want to swim early in the morning, running your pool heater at night would be necessary.

Pool owners have found that by night, without any type of heat source, the swimming pool water temperature can quickly decrease. In some instances, it’s as much as four or five degrees.

That might not sound like much, but once you dip your toes into the pool, you’ll realize that it’s quite a deal colder than you thought.

Why do swimming pools lose heat at night?

It’s a combination of colder temperatures and evaporation. If the difference between the air temperature and the pool water temperature is too striking, the water in your pool can begin to evaporate.

Okay, but are you supposed to leave the pool heater on all night? Not necessarily. You can always heat the pool for a couple of hours until it’s close to your desired temperature. Then you can toss a solar swimming cover over the water.

A cover such as this one by In the Swim can raise the temperature upwards of 10 degrees if exposed to consistent sunlight for five to seven days. Even if the weather in the days prior was cloudy, the presence of the cover will hold in the heat of the water, so it doesn’t cool as rapidly as it would without a cover.

A common concern about pool covers is if you can run the pump with it on. We have an article on exactly this: Can You Run Your Pool Pump With The Swimming Pool Cover On?

Solar Pool Cover

backyard pool with cover
A solar pool cover will keep the heat in

Click here to check the price >>

The Pros of Heating Your Pool During the Day

As the last section proves, there are advantages to heating your pool both by day and by night. Since you’re likelier to do the former than the latter, let’s begin by discussing the benefits of daytime pool heating.

Sunlight Can Speed up Heating

One of the biggest benefits by far of warming up the pool water in the daytime is you have the assistance of sunlight.

Sunlight is warmth, and warmth in the air is soon converted to warmth in your pool thanks to your heater, as we talked about. The sun can keep the pool heater working efficiently, increasing the water temperature degree after degree until you’re ready to jump right in.

Even on those days when you don’t see the sun, that doesn’t mean it’s not there. It’s hiding behind the clouds. Its warmth won’t be as strong but compared to heating your swimming pool at night, it’s more advantageous to do so on a cloudy day most of the time.  

Warmer Temperatures

This goes back to what we talked about in the last section. In which scenario does it sound more convenient to heat your pool? A.) When the water is already 40 degrees? or B.) When the water is 25 degrees?

Sure, in either scenario, the water is cold, but it’s 15 degrees warmer in the first scenario. The higher the temperature baseline, the less time you have to run the pool pump. The only exception would be if you wanted to raise the pool water temperature to a very high degree compared to its starting temperature.

The additional warmth from the daylight will save you time in running your pool heater, and that can prolong its lifespan.

Most People Use Their Pool During the Daylight Hours

The best time to heat your swimming pool is before you want to use it, and most people who enjoy off-season swimming do so during the daytime. Even in a heated pool, once the sun goes down, the air temperature can drop to such a degree that it’s too cold to continue swimming.

When you heat your pool during the day, it’s always ready for you to take a dip!

The Pros of Heating Your Pool at Night

In scenarios like those we described earlier, heating your pool at night is the better solution. Here are some benefits of nighttime water heating.

Some Pool Owners Say It’s Cheaper

It’s generally agreed upon that heating your pool for six consecutive hours is going to cost more than a staggered approach for two or three hours during the day. Yet some pool owners swear by heating their pool at night because they say it saves them more money.

The reason? By maintaining the pool temperature overnight, these pool owners prevent plummeting water temps. In the morning, their pools should be warmer than the pool would be if they had left the heater off all night.

Since the water is already at a good temperature, the pool owner wouldn’t have to run the heater as high and for as long during the day since the temperature is already close to optimal. This is where the purported money savings of this method likely come into play.

Set It and Forget It

The issue with taking a staggered approach to heating your pool is that you have to be around to start and stop the pump. Unless of course, you invest in a pool timer with multiple programs.

Like this timer one here:

Honeywell Industrial Programmable Timer
Programmable Timer

Click here to check the price >>

With overnight heating, you turn the heater on, go inside, get some sleep, and then power it down by the morning. It’s one less thing to worry about on hectic weekdays.

The Pool is Warm for Early Morning Swims

Some people like to shower in the morning to get ready for work. You prefer to start your day by taking a refreshing dip into the pool. The water temperature will be conducive to that since you adequately heated it overnight.

Is It Cheaper to Heat a Pool at Night or by Day?

So, are the pool owners who heat their pools at night correct? Is this really the correct approach?

There’s certainly sound logic behind heating your pool at night. If you allow the water temperature to plummet, then your pool heater has to work that much harder in the morning. The higher rate of output can reduce the heating efficiency, which means the heater takes longer to bring the water to your desired temperature.

Some pool owners who heat their swimming pools nightly say that per month, their heating habit raises fuel usage by 10 to 20 percent more. This fuel usage remains consistent so at least the prices are predictable.

There are some savings to be made at night if you have a heat pump. You may get off peak electricity. If off peak power is available in your area, the rates are generally much cheaper than daytime power rates. So you must also take this into consideration.

Ideally, the best way to save money when using a pool heater is to turn the heat on for a few hours before you use the pool, then put on a solar blanket cover when you’re not in the pool. Leave the cover on until you swim again. This is especially true if you only swim a couple of times a week – there’s certainly no point heating your pool 7 days a week if you only use it for 2 days.

Another option is to keep the heater on around the clock but on a low setting. The pool water temperature won’t go up by too many degrees, per se, but the temps should remain consistent.

Factors That Can Affect Your Pool Heating Cost

How much money you’ll spend to heat your pool by day or night varies depending on a handful of factors. Let’s wrap up by discussing those factors now.

Pool Size

If yours is a small plunge pool, it has less water and will heat quite fast, even at night. The larger your pool is, the longer the heater will have to work to bring the many gallons of water to roughly the same temperature.

Outside Air Temperature

Air-source heat pumps only work well when temperatures are around 50 degrees Fahrenheit or higher. Once the temps dip down lower than that, the pump cannot pull the warmth from the air and transfer it to your pool.

On a very cold day, your heater will run and run but not do anything useful.

Plus, the pool’s water temperature varies greatly depending on the outside air temperature. The warmer it is outside, the warmer the water is to start with.

Heater Output

How big is your pool heater? A greater size increases its rate of output, but the size of the heater should be dictated by the specs of your pool.

Type of Pool Heater

Out of all the heating options, gas is the fastest heating, followed by heat pumps then solar. Gas is also the most expensive, followed by heat pumps. The most economical to run is solar.

Here’s a full rundown on the best types of pool heaters:
Top 4 Pool Heating Options

Solar Cover vs. None

We really can’t stress enough that a solar cover is one of the most valuable tools in retaining pool water heat without running your pool heater all day and night. A cover is low-cost enough that you should try one for a few weeks. You’ll certainly notice a temperature difference!

Conclusion

The best time to heat your pool is during the day at least several hours before you plan on using it. The risk of running your pool pump overnight is that the outdoor temperature might be too low for the pump to efficiently warm your swimming pool. You’ll end up spending a lot of money too.

Now that you know when to heat your pool pump, you can schedule heater usage so you always have warm pool water awaiting you no matter the time of year!

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