How Full Do You Fill a Hot Tub?

Getting the water level right in your hot tub is vitally important as, if it is too full or too empty it can stop the water from being filtered properly and put excessive strain on your pump and hot tub components. Most hot tub handbooks will tell you how full to fill your hot tub but what if you have lost it or the handbook isn’t clear? I decided to look into the question and here is what I found out:

So, how full do you fill a hot tub? The water in your hot tub needs to be two or three inches above the jets and/or above the filter on the side of the hot tub. There might also be a fill mark on the side of the hot tub. The level will need periodically topping up due to splashing and water evaporation.

Why is the water level in your hot tub so important?

The water level in your hot tub has to be at the right level for the correct operation of the hot tub. If you think about it all of the components in the hot tub from the pump to the heating element will have been designed to work with a very specific volume of water. If your hot tub has an electronic display or any kind of automation then the hot tub’s “brain” will assume that it is working with a set volume of water and it won’t be able to work correctly if this isn’t the case.

If you are adding chemicals to your hot tub or, in fact using any type of sanitization method, then you will need to know the exact volume of water you are working with in order to get the levels of sanitizer correct. Too much sanitizer can lead to problems of skin irritation and breathing problems and too little is equally problematic in that your hot tub may not be adequately cleaned and bacteria and algae can start to form.

On a more practical level if the water level is below the jets then the water won’t move round and it’s possible that without the resistance of the correct amount of water that the pumps may overwork and get damaged. If the level is below the filter inlet or outlet then the water won’t get filtered correctly and this will inevitably lead to a build up of dirt and debris in the water which can harbour germs and bacteria.

Similarly, if the water level is too high then the water will potentially overflow when you get in the hot tub. Again the sanitizer level could potentially be too dilute leading to problems with cleanliness and the pump and heater may have to work extra hard to move and heat the water leading to extra energy usage and wear and tear.

So, it’s important that you fill your hot tub to the correct level with water and that you periodically check it and top up if needed. So, the first thing to do is to have a look in your hot tub’s handbook and see if you can find any information in there about filling to the correct level. If not then a look online might help or a quick call to the dealer where you bought the hot tub. If none of this works or is possible then look for a fill mark on the side of the hot tub.

If you can’t find any definite information on the right fill level then fill to a point two or three inches above the highest jet or filter housing – whichever is the highest.

It’s important to refill when needed and equally important that, if you do need to add more water, that you check and top up your sanitizer levels afterwards to make sure that the sanitizer hasn’t become too diluted to be effective.

How do you fill a hot tub with water?

Once you know the level of water you are aiming for actually filling the hot tub up with water is quite straightforward:

Check the hot tub is clean – First of all check that the actual hot tub shell is squeaky clean as you don’t want to introduce any extra dirt or bacteria at this point. If you haven’t done it already use a hot tub shell cleaning solution to wipe away and grime. Look carefully around all of the fittings for any mould or algae growth and clean away as much as possible. Once you have cleaned the hot tub rinse it out with clean fresh water to get rid of any excess dirt or cleaning fluid both of which could pollute your hot tub water and potentially lead to foaming or cloudiness.

Once you have done this and you are sure that there is no dirt or dirty water in the bottom of the hot tub replace the drain plug and switch off the power.

Check the fill area – You can just put your garden hose straight into the main part of the hot tub and start filling up but most hot tub handbooks will recommend removing one of the filters and filling up through the filter housing. the reason for this is that it prevents airlocks forming in the hot tub’s plumbing and therefore makes for a smoother first start up.

Use an in-hose filter – Use a filter on the hose to remove and dirt particles from the water as well as any excess metals. This is a simple but important step that can prevent dirt and water chemistry problems further down the line.

Sit back and wait – So now there’s little to do apart from sitting back and waiting until the hot tub fills up to the correct level. Once it has done this switch off the water, remove the hose, replace the filter if you removed it and switch the power back on.

Run the start-up programme – Some older hot tubs may not have one but the chances are that your hot tub will have a start up or primer programme. Generally speaking, this is designed to expel any airlocks from the system and to distribute the water evenly before the heating process starts. Often the hot tub will run one pump at a time in sequence to makes sure that the water is correctly dispersed. Once the start up programme has run check the water level again and top up if needed. The hot tub can now be heated.

Set up your sanitization system – Make sure that your filters are clean and then start by getting the water chemistry correct. Check the total alkalinity of the water first and then the PH levels. Only when these are correct can you then start using your sanitizer. Remember to check the levels carefully and make sure that you do not get into the hot tub until everything is at the safe and recommended level.

Check out my simple guide to hot tub maintenance here to help you out with this.

Related Questions:

How much water does it take to fill a hot tub? It will depend upon the size of the hot tub but typically a hot tub will hold between 400 and 600 gallons of water. To put this in context a load of laundry uses between 20 and 40 gallons and, if you only change your hot tub water every 3 – 4 months, the amount of water used when compared to the total usage of the average household is negligible.

Should a hot tub be filled with hard or soft water? Soft water can be damaging to hot tubs as it has often been artificially softened in a domestic hot water system. Similarly, excessively hard water can lead to corrosion and build-up of mineral deposits. The solution is to regularly check the calcium hardness level in your hot tub and to add calcium hardness if you need to. If there is too much calcium on the water then the only thing you can do is to drain the hot tub and to refill through an inline hose filter.

Can I fill my hot tub with warm water? Theoretically, you can fill a hot tub with warm water but there are a number of problems that this might produce. The water will need to be kept below 40 degrees celsius to stop the hot tub from cutting out, the hot water system may be damaged by the amount and pressure of water needed, there could be additional bacteria in the warm water, the hot tub shell may be damaged by becoming too warm too fast and you may not be able to filter the water as you add it.

So, the general advice is that filling with warm water is not a good idea. The best course of action is to follow the advice above and the advice in your hot tub’s instruction manual and to fill with cold water.

For more detail have a look at my post here.