Can You Fill a Hot Tub With Cold Water

Hot tubs are expensive. And even though filling one up seems easy, you don’t want to make any mistakes. One of the things most new hot tub owners worry about is filling their tubs with cold water.

You can fill your tub with cold water and even take ice baths in it. This doesn’t damage the tub or its heating equipment. From a health and safety perspective, it is even better to fill the tub with cold water before heating it, but this can affect your electric bill negatively.

In this article, you will learn how lukewarm, hot, and cold water affect your hot tub and the electric bill it incurs. But much more important is the section right after, which goes over the right steps to fill up an empty hot tub.

Filling Your Tub With Lukewarm vs. Cold Water

If you live in a sunny state, your tap/hose water might be lukewarm. In that case, you might wonder if you should just fill your tub with it or if you need cold water.

You fill your hot tub with whichever water temperature is more convenient as long as it is not hot enough to damage the tub material. Lukewarm water that comes from an external tap in sunny states is okay to use in a hot tub. It saves money as well because the tub doesn’t have to heat up a significant volume of chilled water.

The problem is, this is mostly out of your control. Generally, people with hot tubs live in relatively colder areas. And if your garden tap delivers cold water, you have to fill your tub with it. In my estimation, the difference in the electric bill is dictated by the weather more than the temperature at which you fill the hot tub.

The water’s baseline temperature outside the 8 hours you run the heat pump will remain the same. In other words, it is not worth the effort to make cold tap water lukewarm before adding it to the hot tub.

What if You Have a Hot Water Tap?

In the previous section, we figured that using lukewarm water is beneficial if it is the starting temperature of your garden hose. Otherwise, using cold water isn’t problematic.

So what about hot water faucets/taps? You can use hot water to fill your hot tub and save the initial heating cost. But when the heat pump goes idle, the water temperature will return to what your region’s climate decides. Similarly, filling your tub with cold water will raise the heating cost the first time you turn on the heat pump.

After that, the tub doesn’t know that the water was once ice cold. It will go back to being the temperature that the climate allows it to be soon after you turn off your heat pump. So, is filling the tub with hot water worth draining your Geyser tank to save a few dollars? You decide.

The Best Way To Fill Your Hot Tub With Water

Knowing that the temperature of the water doesn’t matter as much, you can confidently fill up your hot tub. But before you do, you need to make sure that at no point is the water over 104F while you’re filling it. If you want further surety, follow these steps to fill up your hot tub for the first time.

Place Your Hot Tub Where You Intend To Keep It 

Remember, the hot tub might be hard to move empty, but it is nearly impossible to fill when full. So placing it in its intended final spot is very important. If you think you have it exactly where you want to keep it, just make sure you’ve read my post on how far the hot tub needs to be from your house.

Add a Prefilter to Your Garden Hose 

Prefiltering tap water is an essential step that makes your hot tub last longer. These aren’t exclusive to filling the tub for the first time. You need the skimmable solids out of the tap/hose water before it goes into your hot tub. Hose prefilter attachments are easily available on amazon.

Estimate the Intended Water Level 

Different hot tubs have different water holding capacities and, consequently, minimum water requirements. Water should cover all jets at a minimum. Even when the water is not still, the jets shouldn’t be exposed to air while they’re in circulating mode. If air gets into the circulation, your heat pump is bound to burn and fail eventually. 

Make sure every water circulation office stays fully immersed in water regardless of the splashes and waves that people make in the pool. This is yet another practice that should not be limited to the first time you fill a hot tub.

Run the Hose Through the Skimmer Basket 

It is quite crucial to run the hose through an inlet into the tub’s circulation instead of letting it in the middle of the tub. If you fill up the tub without considering the circulation system, there might be air pockets in it that would burn out the heater. 

Every hot tub has an inlet from which the water is sucked in and passed through the heat pump. You need to start filling water in the inlet until the circulation system’s return jets fill up the middle of the hot tub. You don’t need to do this when you’re topping up your hot tub once you’re using it.

Run the Jets Without Turning on the Heat 

To be on the safe side, you should run the hot tub’s water circulation with the heat pump turned off. This ensures that the process of circulating water cleanses the system of any air. Once the water is circulating smoothly, you can turn on the heat. This is a good practice for any time you add more water to your hot tub, but it is especially useful for the first time you fill your hot tub with cold water.

Final Thoughts

You can fill a hot tub with cold water or hot water (below 104F). The water level is more important than the water temperature. You need to immerse all water inlets and outlets in the tub’s interior with water to avoid damaging your water heater.

Jed Arnold

Jed spent every year from the ages of 15 - 22 as a Lifeguard (Red Cross) and ages of 17 - 22 as a Certified Pool Operator (CPO). Between working for over a dozen facilities and owning a pool, he carries over a decade of pool experience.

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