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How Long Does It Take To Heat up a Hot Tub?

Written by Elizabeth Fincher

How long your hot tub will take to heat up the water depends on a number of factors. The most impactful factors are the heater quality, how good your insulation is, how well your cover can trap heat, and the temperature outside.

How Long Does It Take To Heat up a Hot Tub

There are also some factors with minor effects on the heating process. Let’s explore the factors that may slow down the heating process of your hot tub water and how you can speed up the process.

How Long Does It Take To Heat up a Hot Tub?

On average, it takes anywhere between 4-20 hours or more to fully heat up your hot tub. Water heats up at a rate of about 3-6 degrees per hour. There are a lot of factors that control the heating up process of your hot tub water. We’ll know about those factors in a bit.

The average temperature of the water pouring through USA households is around 50°F. Given that the maximum temperature your hot tub water should reach is 104°F and your water temperature is rising at 3°F/hour, the time it would take to heat up your hot tub water is:

(Maximum hot tub temp – Average tap water temp) / Rate of temp increasing

= (104 – 50)/3  = 54/3  = 18 hours.

heat up a hot tub

There are numerous factors that contribute to the duration of your hot tub water heating up. Let’s check them out.

What Controls the Heating Process

Starting temperature

This may sound counterintuitive to some people, but the initial temperature of the water has a significant impact on the time you’ll need to heat your hot tub water up.

Many leave their hot tubs on all day but that can have a negative effect on your bills. The higher the base temp of the water is, the quicker it will heat up.

Ambient temperature

You also have to take the ambient temperature of your area into account to determine the time it would take to heat up the water. If it’s freezing or windy outside, your spa water will take much more time to heat up than if it’s a warm sunny day outside.

You can try to isolate your hot tub from the surroundings to reduce the effect of ambient temperature. However, that can become a labor and money-intensive project.

Position

The ambient temperature of your hot tub’s surroundings also depends on the position of the hot tub. If a hot tub has shelter from wind force and gets a lot of sunlight throughout the day, it will heat up quicker.

On the contrary, if your tub is exposed to wind or doesn’t get enough sun, it will take a lot of time to heat the water up.

Hot tub cover and insulation

Hot tub covers are designed to trap the heat inside so the water stays warm for a long time. The cover separates the water from the airflow above and helps to retain the heat. Covering up your hot tub during the heating process can reduce the time needed to heat the water.

The insulation of your hot tub world in a similar way. The quality of your hot tub insulation and cover will affect the time needed to reach the maximum temperature. It is the easiest way to speed up the heating process. Adding a floating spa cover over the water will also help.

Size of the hot tub

Larger hot tubs have a wide water surface area which helps the water to dissipate the heat much faster than smaller tubs. It’s just like when you boil water on your stove. Water in a larger pot takes more time to heat up (boil) than in a small pot.

Regular maintenance

The key to keeping your hot tub in top-notch condition is regular maintenance. Make sure there are no cracks in the insulation or in the cover. If you ignore the maintenance routine, your hot tub’s integrity will get weaker over time and it will take more time to heat the water.

This is how you maintain your hot tub: 

It’s your job to clean/replace the filters, check the insulation, and make sure that the jets and pumps are working efficiently. That way, it’ll take significantly less time for the water to be ready for a relaxing soak.

The status of the jets

The job of your waterjets is to circulate water and heat evenly across the hot tub. This is true that water jets will mix cold water with the hot water from the tub, and this may seem that it will take a bit longer to heat up the water, but it’s a great way to distribute the heat evenly.

If your jets are turned off during this process, there may still be some cold pockets in the water where heat won’t reach evenly.  It’s a good practice to leave the jet on while you are heating up the hot tub.

Quality heater

This is another factor that directly affects the heating process. If your heater is cheap and less efficient, it will take longer. On the other hand, a powerful heater that heats up water by 6-10 degrees per hour will significantly cut the heating time short.

The heater that came with your hot tub is like a default setting. You can install quality aftermarket heaters to help the water heat up quickly. Superior quality heaters will offer higher BTUs per hour, higher wattage, and improved sensors/controls.

All of these features will make your hot tub more efficient and heat up the water faster. A quality heater will also help you save some money down the line as reduced heating time will help you save a lot of power.

Water chemistry

When you start heating the water up in your hot tub, chemicals dissolved in the water will heat up too. That will result in some heat loss and it’ll take more time and effort to heat up the water.

Chemicals like alkaline can build up scales over time and your hot tub will have to put more energy and effort into heating the water. That is why regular maintenance is the key to keeping the hot tub efficient and cutting down the time needed to heat the water.

Tips to Heat Your Hot Tub Faster

  • Place your hot tub in an isolated area, far from the wind
  • Keep your hot tub covered and well-insulated
  • Use a  floating spa cover for additional heat-trapping
  • Install a quality aftermarket heater
  • If possible, take advantage of the natural heat source, the sun
  • Turn the water jets on. Make sure the tub is full and the jets are submerged
  • Don’t put hot water directly into the tub. It will damage the parts
  • Enclose the hot tub in a gazebo if the tub is placed outside
  • Keep the hot tub under regular maintenance
  • Regularly check the water quality and bleach the water if necessary.

FAQs

1. Do the jets have to be on to heat a hot tub?

Ans: Not necessarily. You can also heat up the water when the jets are turned off. However, doing so may leave some cold pockets/spots in the hot tub as the heat won’t be distributed evenly. Keeping the jets on during the heating process is a good practice.

2. Is 40 degrees hot enough for a hot tub?

Ans: Yes, 40°C (104°F) is hot enough for a hot tub. According to The British and Irish Spa and Hot Tub Association (BISHTA), it is the highest safe hot tub temperature and most of the industry agrees with that. Anything hotter can be potentially harmful and we should avoid that.

About the author

Elizabeth Fincher

Elizabeth started her career as an interior design artist at a multinational interior design farm. She completed her masters degree from the University of North Texas back in 2010. She was also a Spelling Bee runner-up when she was 14. She took interest in bathroom interior designing after joining her first job. Later she started her own firm as an independent artist. She’s been one of the founding members of Toiletsguide. She examines the design and ergonomics of the units we review and directs the interior decoration team of our in-house research facility. Elizabeth plays piano masterfully and always finds time to entertain us in between our busy schedules.

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