How High Should You Fill Your Hot Tub? (A Simple Guide)


Unfortunately, not all spa manufacturers display a water fill line, which seems crazy given the potential damage that can be caused when there is too much or too little water. So how do you identify the correct fill level?

You should fill a hot tub to a maximum height of 2 to 3 inches (5 – 7.5cm) above the top of the filter. The water must cover all the jets but be below the headrests to prevent the material from rotting. Make sure to take into account the number of users as the water level will rise when people get in.

There are huge consequences if you don’t fill your hot tub to the right level. In this article, I’ll show you:

  • The dangers of adding too much water
  • The dangers of adding too little water
  • How to properly fill your hot tub for the first time

Can you put too much water in a hot tub?

If you have little experience with owning hot tubs, it’s all too easy to accidentally overfill. But what happens if you do fill with too much water?

If you overfill a hot tub, it can cause damage to any electrical components that aren’t insulated against water damage. If the water level rises above the loop for the air blower, it will cause the circuit breaker to trip. Overflowing water will damage the surrounding area and may accumulate beneath the spa if it’s not level.

When filling a hot tub, many forget to factor in that bathers are going to get in, which raises the water level significantly.

While not all spas are damaged by overfilling, many models are. So it’s better to be safe than sorry as you don’t want to find out the hard way.

No one wants to stand there watching their hot tub fill with water, but it can be difficult to estimate the time it’ll take to reach the correct level.

That’s why I wrote a guide on accurately estimating the amount of time it takes to fill a hot tub.

For absolute peace of mind, I recommend attaching an inexpensive water timerOpens in a new tab. between the faucet and hose to shut the water flow off automatically at a time of your choosing.

If you accidentally overfill your spa and it’s no longer working, then you’ll need to reset the breaker. Unfortunately, resetting doesn’t always work, in which case you’ll need to consult a professional.

Water that spills over the sides can also cause damage to the surrounding area, which is why it’s a good idea to use water-safe materials around your hot tub.

Ensure that your spa is perfectly level to avoid standing water, and always keep the area around the spa clean and dry after you’ve finished soaking.

In order to remove excess water from your hot tub, turn off the power at the circuit breaker and partially drain the hot tub using a hose or sump pumpOpens in a new tab..

If your sump pump’s outflow hose isn’t long enough to reach the drain, connect it to a garden hose.

What happens if hot tub water gets too low?

The results can be equally devastating if you under-fill your hot tub. Ensure that the water level never falls below the minimum level.

If the water level in your hot tub is too low, the pump will be overworked and will suck in air, eventually destroying it. The water level will naturally lower by around 1 inch (2.5cm) per week due to evaporation and spilling as bathers exit the spa, so you must perform regular water top-ups.

Yes, your hot tub really is like Goldilocks: not too much and not too little.

It’s necessary to keep the water topped up every 1 to 2 weeks to avoid causing damage to the spa’s pumps. Remember to test and adjust the water chemistryOpens in a new tab. after each top-up.

If the water level is too low, it will not flow through the filters, causing damage to the spa and potential health risks to you as the water become more and more unsanitary.

If you leave your hot tub uncovered, then you may see the water level lower by as much as 2 inches (5cm) each week, and possibly more during the cold winter months.

However, if you’re noticing a significant loss in water, then it may be sign of a leak. The cause may be anything from a crack in the hot tub’s shell to leaks within the seals, pipes, or fittings.

If you suspect there is a leak, don’t delay in getting your spa repaired. And if you go trying to locate the leak, make sure to cut the power by flipping the breaker switch to avoid electrocution.

How to fill a hot tub for the first time

There are a few things you need to do you fill your hot tub for the first time. First, ensure that the spa is in its final resting area as you won’t be able to move it once it’s filled with water.

Now read through all the following steps carefully before attempting to fill your hot tub for the first time.

Secure any loose connections

Pump connections can become loose during transportation, so it’s important to remove the front cabinet (the side where the control pad is) to tighten and secure any fittings that have come loose.

Keep the cabinet off as you fill your spa for the first time so that you can keep an eye on everything to ensure the connections are watertight.

Clean and rinse

Before filling your spa, you must always make sure that all the surfaces are as clean as possible. Use this specially formulated cleaning solutionOpens in a new tab. and wipe the hot tub shell and cover clean using a soft cloth or sponge.

Rinse thoroughly and remove the rinse water using a portable wet/dry vacOpens in a new tab. or by hand with a soft cloth.

Remember: water and electricity do not mix. Whenever you carry out any cleaning, always make sure to disconnect all power to your hot tub to avoid electrocution. Unplug the hot tub and turn off the circuit breaker so you’re in no doubt whatsoever.

Install filters

Install a filter cartridgeOpens in a new tab. into each filter well. Many hot tubs have only one filter well, but be sure to check your owner’s manual to be safe.

Get your garden hose and attach the pre-filterOpens in a new tab. to the end. Pre-filters are an absolute necessity.

They remove a lot of impurities and unwanted particles (suspended solids) from the water, helping to reduce the number of chemicals needed to balance the water chemistry later on.

Begin filling with water

Rather than placing your garden hose in the footwell, it’s better to place it inside the filter well. The first benefit of doing so is that it adds an extra layer of filtration.

The second benefit is that having the water flow through the filters helps to lower the risk of any dreaded airlocks from occurring, which can be hugely problematic when you later start up your hot tub.

Start filling with fresh, cold water and double-check that the hose is still in place at the bottom of the filter well.

Once the water has filled the footwells, add your sequestering agent according to packet instructions to combat any suspended solids in the water.

Allow the sequestering agent to filter through for at least 30 minutes before adding any other chemicals. Never mix chemicals.

Set an alarm

Now it’s just a case of waiting until the water reaches the minimum fill level. If you don’t want to stand there watching, then set a timer or an alarm to ensure you don’t forget.

I always use the alarm on my phone whenever I’m filling with water. Trust me, it may sound crazy, but it’s so easy to forget. Set. That. Alarm.

Once you’ve reached the minimum fill level, add a little more based on the number of people that are going to be in the tub at any one time.

You’re looking for the water level to be around an inch below the headrests but high enough to fully cover all the jets.

Now remove the hose, reattach the filter housing lid, plug in and turn the breaker on.

Prime the pump

Priming is vitally important as it activates the pump prior to the heat cycles beginning, cycling each pump to purge any air from the plumbing.

Airlocks can result in instantaneous heater failure, also known as “dry firing”. Dry firing is not covered under warranty, so be extra cautious.

The process of priming depends on your particular model of hot tub. Some control panels have a self-priming mode, but others require it to be carried out manually using a bleeder valve.

Heat the water

Once the priming mode has finished, check for leaks around couplers on the pumps and heater housing. Hand tighten if necessary.

Reattach the cabinet panel and begin heating the water, adding your chemicals once the temperature reaches 80°F (27°C).

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