Your hot tub has finally arrived and you can’t wait to get in, so standing there watching it fill up seems like a lifetime. So how long does it take to fill a hot tub exactly?
An average-sized 300-gallon hot tub takes between 90 and 120 minutes to fill. Factors that influence fill time are water pressure, water flow rate, length and diameter of the hose, the time of day, and where you live. You can estimate the exact fill time by timing how long it takes to fill one gallon with your hose.
Besides fill time, there are other questions such as how far to fill up and whether it’s okay to add a little extra water? Read on to discover why getting the answers to those questions is so important.
Water pressure
The water pressure has an enormous impact on how long it takes to fill your hot tub. If you have poor water pressure, it’s going to slow the time down considerably.
Where your property is located has a huge impact on water pressure. Many people that live in rural areas rely on well water, which often has lower water pressure.
If you live in or town or city with a considerable population, you’ll usually find that you have higher water pressure levels.
As a general rule, mains water pressure depends on how far away your home is from the nearest reservoir or supply.
Having said that, water pressure can vary greatly from someone living in the same street as you. For example, if you live at the top of a hill, your water pressure is likely to be weaker than the homes at the bottom.
The water pressure can also change depending on the time of the day. You may have noticed that the pressure is lower than normal in the early morning as more people are showering or in the evening when people are watering their yard.
The majority of homeowners use an outside hose pipe to fill their hot tubs, and the water pressure is affected by the length and diameter of the hose being used.
Water flow
Pressure and flow rate are two different things. Water flow is how much water comes out of your pipes, and water pressure is the amount of force the water has when it exits the pipe.
Pressure affects flow rate. If the pressure increases, then the flow rate increases with it. If the diameter of your hose is very narrow, it’ll have a lot of flow rate but with greater pressure.
Hose size
Having a wide diameter means that the water has a greater flow. Basically, more water is able to pass through because it’s so much bigger.
Standard-sized hoses are usually 3/4”, but you’ll find diameters anywhere from 1/2” to 2” (12 – 25mm). Purchasing a 2-inch hose
will dramatically speed up the time it takes to fill up your hot tub.
The size of the hot tub
It doesn’t take a genius to work out that the amount of time it takes to fill your hot tub depends on its capacity. The average spa is about 300 gallons, but sizes range from 150 to 700 gallons.
The average water flow rate from a hose is between 2.5 and 3.3 gallons per minute. This equates to:
| Capacity (gallons) | Time to fill (2.5 gal/min) | Time to fill (3.3 gal/min) |
|---|---|---|
| 150 | 60 | 45 |
| 300 | 120 | 90 |
| 500 | 200 | 150 |
| 700 | 280 | 210 |
You definitely won’t want to stand and watch your hot tub fill up, but I speak from experience when I say that it’s very easy to walk away and forget you’re filling with water, which can be a disaster.
The best thing to do is to set a timer on your phone so that you don’t go flooding your yard. But how long to set the timer? Well, here’s a great way to estimate the fill time:
- Grab a large measuring jug
- Get your stopwatch ready
- Start your stopwatch and fill the jug for 6 seconds from your hose (not kitchen faucet)
- Multiply the quantity of water by 10
By multiplying by 10, this gives you a good idea of how much water flows from your hose per 60 seconds. For an even more accurate reading, I like to run the water for 60 seconds.
The only issue with running for so long is finding a measuring jug large enough to hold and record the amount of water.
A word of warning: when it comes to filling your hot tub, make sure the power is turned off to prevent electrocution and damage to the pump from having it run dry. Check out my guide on how to fill your hot tub properly.
Where should I fill my hot tub up to?
Because all of the components inside your hot tub have been designed to work with a specific volume of water, there is a minimum amount necessary for safe operation.
Hot tubs must be filled to the fill line marked on the side. If there is no fill line, fill the hot tub 2 or 3 inches (5 – 8cm) above the jets and filters, whichever is higher. It’s necessary to top up the water from time to time to replace water that is lost through entering and exiting, splashing, or evaporation.
Never allow your hot tub water level to fall below the jets or filter housing as this will cause significant damage. Low water levels will cause the heater and pump to shut down.
You risk overworking the pump and having air sucked into it. It also means that there’s no outflow from the jets and a lack of filtration from the filters.
Water is continually being lost even when the hot tub is not in use, so make sure to make regular water level checks.
Also, remember to adjust the chemical balance of your water each time you top up.
Never overfill your hot tub
Hot tubs aren’t all that deep, so you might be tempted to fill above the water line to keep as much of your body submerged as possible. So can you fill a hot tub too full?
You should never fill a hot tub above the fill line as it can cause irreparable damage. Overflowing water can result in damage to the electrical components that aren’t insulated. Water spilling over the sides can also damage the surrounding area. This is particularly true with concrete bases, which can crack when wet.
Ensure that the water level is always a good inch below the headrests (pillows) too. The chemicals in the water can cause the laminate on the pillows to break up, causing the internal rubber to flake off.
Remember that the water level is going to rise as soon as you turn on the jets. And when you and your family get into the hot tub, a hot tub that has been overfilled can quickly overflow.
It goes without saying (but I’ll say it anyway) that you never ever want to risk overfilling your hot tub if it’s indoors. That could be a very expensive repair job indeed.
Can you fill a hot tub with hot water?
Hot tubs can take a long time to heat up once they’ve been filled, using quite a bit of electricity in the process. So is it possible to save time and money by filling your hot tub with hot water?
While it’s possible to fill a hot tub with hot water, it’s not advised. In order to fill a hot tub with hot water using the correct technique, remove the airlock and slowly add the hot water to the cold. Beware, if the water is too hot or has been softened, it’ll damage the hot tub, voiding the warranty.
If you’re absolutely sure that your home’s water hasn’t been treated with softeners, then you could save some money and time. However, I don’t think the risk is worth it.
The last thing you want is to cause corrosion to your hot tub shell as this will void your warranty and result in costly repairs.
I totally get that all you want to do is get in your hot tub as soon as possible and start relaxing, but there are better ways to go about heating your hot tub more quickly.
Did I cover everything?
I always try to provide the most relevant and up-to-date information I can in all of my articles. Saying that, feel free to shoot me an email using the contact form if you think this article is lacking in some way, or if you’ve been left with any doubts.
Thanks for reading and happy hot-tubbing!
