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Can You Add Boiling or Warm Water to Hot Tub?

can i fill my hot tub with warm water

Wondering if you can add boiling water to hot tub to speed up the heating process?.  Well, keep reading to find out whether it is possible or not and if it is possible what are the risks involved.

You’ll agree with me that hot tubs are so relaxing especially after a stressful day. But having a hot also comes with additional electricity costs and it can sometimes take as much as 24 hours fr a full hot tub to heat up to a working temperature from cold.

adding boiling water to hot tub

So, it may look like is a good idea to fill your hot tub with warm water to help you save on the electricity bill and to skip the waiting time required to properly heat up your hot tub.

Here is a short answer to your question.

As much as possible avoid adding boiling water to your hot tub. Here is why. Generally, most heaters have a temperature set between 120 and 140 degrees. Hot tubs are designed for a maximum temp of 104 degrees Fahrenheit. So, as you can see, adding boiling water to the hot tub can damage the hot tub.

Besides the temperature difference, corrosion and excess foam can also happen if the water added is from a water softener.

But let’s look at the other issues that can also arise as a result of adding hot water to your hot tub.

Read on to find out more.

Can You Put Boiling Water to Hot Tub?

Not only do hot tubs consume a lot of electricity, but they can also take a lot of time to heat up to the optimum temperature. If you’re in hurry, this may seem like it’s forever.

Sometimes, it can even take up to 24 hours for heating. But that being said, 3-8 hours is more of the typical range to heat a hot tub starting with the temperature from your garden hose.

You Risk Damaging the Hot Tub Shell. If you wish to add boiling water to your hot tub and you are wondering whether it is possible, then the answer is yes. You can add boiling water to your hot tub. But there are risks associated with doing it.

First of all, the biggest risk of adding boiling water to your hot tub is it will damage the hot tub shell.

Problems with soft water: Also, can household water can also contain water softeners, and if anything goes wrong with the hot tub, this act can invalidate the hot tub warranties if you have added soft water to the hot tub.

If the water in your hot tub is soft, it can cause corrosion to the internal working parts of the hot tub. Also, if the water is too hard, it may cause calcium deposits.

Hot Water System Capacity. Also, if your aim is to fill the hot tub with boiling water, you will agree with me that it can take a long time to accomplish it.

Most hot water tanks at home are about 180 liters. This obviously is not enough capacity if you wish to fill the tub.

Temperature Cut Out. Another problem that might arise as a result of adding hot water to the hot tub is it will probably trip the temperature cut out on your tub heater. This will mean that the hot tub may not work because it will be protecting itself from excessive temperature.

This can in turn damage the internal electronics of the hot tub if the water is too hot. So, besides damaging the tub shell, you can also risk damaging the internal working mechanism of the hot tub.

Bacteria and Debris.  Adding hot water to your hot tub without it going through the hot tub filtration system may result in adding bacteria and debris to the hot tub.

In order for your filtration system to clear the bacteria and other debris, it will use extra energy and may require maintenance in terms of filter cleaning and changing.

These are some of the problems you may encounter by adding hot water to your hot tub. Now let us look at how you can heat up your hot tub faster.

What if I still Want to Fill My Hot Tub with  Hot Water?

Well, if after running through the risks, you are still bent on adding the hot water to the tub, you can do it.

Before I get to that in a second, let me say if you are trying to save on energy cost or speed up the hot tub heating process, the benefits are negligible compared to the risks and costs you may incur if you add boiling water straight to the hot tub.

To still go with the process, you will need an additional hose to be able to combine cold and hot water simultaneously and if possible, get a thermometer to keep an eye on the temperature.

This will prevent you from adding too hot water to the hot tub to prevent damaging the hot tub shell.


Considering all these extra costs and time, I and sure if you plan your hot tub bath ahead of time, you can heat it up in an economy mode and when you are ready, you change it to standard mode, this way, it won’t take time for it to heat up to the constant temperature.

To add the hot water, start by quarter filling the hot tub with cold water and then add the hot water. Keep in mind to check the temperature at internals to prevent it from exceeding the standard hot tub temperature.

This will ensure you are in the safe zone. You can balance the cold water with hot water to a certain temperature below the hot tub standard temperature. At that point, you can switch on the hot tub heater to bring the temperature up to the standard temperature.

You will have to also check the water for hardness and softness.

How Can I Heat My Hot Tub Water Faster

I bet the two main reasons why you want to add boiling water to your hot tub are; one, you don’t want to save on the time it takes to heat up the tub, and two, you want to reduce energy costs.

Well, whichever your reason may be,  here are some ways you can help speed up the heating process.

1).  Use a Hot Tub Cover

without a hot tub cover, the heat from the hot tub will escape into the cold air and make it harder for the tub water to heat up.  The hot tub cover is insulated to help trap the heat inside the hot tub.

2). Add a Powerful Heater

most hot tub heaters can be replaced fairly easily.

Do some research on hot tub heaters and get a more powerful heater that will fit well with your hot tub. On the low end, you have 4 kW, but they can range as high as 6kW, and typically the heater assembly can be purchased for under $200.

A more powerful heater will reduce the time it takes to heat up the hot tub to standard temperature.

3). Use Thermal Blanket When Heating Up and When the Hot Tub

A thermal blanket sits on the surface of the water underneath the tub cover. It adds an additional layer of heat insulation to help keep the heat in and prevent heat loss. It also helps prolong the life span of the hot tub cover.

Read More On:

How hot tub thermal blankets work

These are relatively cheap and you can purchase them online at Amazon or at your local hot tub supply shop.

4). Use Your Hot Tub Jets

Turning your jets on improves water circulation and allows your water to be heated more evenly. It eliminates any pockets of cold water and gets all the water flowing through the system, including the heater.

Then, with the lid in place, all that heat and friction just gets put right back into the water.

5). Add Insulation

Hot tubs that are less insulated are affordable while the high-end ones are well insulated.  If you happen to own a less expensive model, the other way to reduce heating time is to add additional insulation such as spray-on foam to insulate under the acrylic shell and around the jets.

You can also use fiberglass boards to insulate on the backside of the panels.

This waterproof thermal energy heat shield can easily be cut into sizes and attached to the hot tub panels or placed around and under the shell for a quick inexpensive insulation upgrade.

can i fill my hot tub with warm water

Why does my hot tub take so long to heat up?

Generally, heating a hot tub shouldn’t take longer than 8 hours to reach its temperature, if it does, then you may be having problems with insulation, a lower-powered heater, a defective thermostat, or a defective heater.

At its lower end, these can add additional 5 hours to the heating time.  It can even take as long as a day to heat up due to many issues but the typical is between 3 and 8 hours.

Here are hosts of reasons why your hot tub may be taking a long time to heat up.

1). Colder Garden Hose Temperature

If the water you are filling your hot tub with is too cold especially in the winter, then rests assured it will take a longer time to heat up.

A garden hose temperature can be as low as 50 degrees or maybe as high as 75 degrees.

This is a wide difference in temp. considering that hot tub water heats between 3-6 degrees per hour. So, with this in mind, even with the most powerful heater, it will still take some hours to heat up.

Here are the main factors that may influence the temperature of your water hose.

  • Time of year
  • Location
  • Is your water from a well?
  • Does it come from a storage tank?

2).  Your Hot Tub Jets and Water Features Aren’t On

If the jets aren’t on or some are not on, it will affect the time it takes the tub to heat up. The jets help in the water circulation and get the tub to heat up quickly.

Closed jets or partially opened jets can affect the heating time.

3). Your Hot Tub Cover is Off or not in Good Shape

The hot tub cover ensures that the hot tub retains heat as much as possible. This in turn maximizes the heating process. If it is damaged or doesn’t exist at all, this will prolong the heating.

Also, make sure your hot tub cover is in good shape.

Final Thoughts on Adding hot Water to Hot Tub

As already stated above, you can add boiling or hot water to your hot tub but it’s not recommended.

The risks involved are many and their effects can be detrimental. Hot water can damage the tub shell, affect your tub internal working mechanisms, may cause corrosion, and affect your hot tub warranty.

There is a reason why hot tubs are designed the way they are in the heating process to. It is not good to alter it because you may be in a hurry or want to cut energy costs.

Either way, if you choose to fill your hot tub with hot water just make sure you heed to the process outlined to minimize the risks.

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