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Does a Hot Tub Heat Up Faster With the Jets On?

When I got my first hot tub, after filling it for the first time and waiting patiently for the water to heat up, I wondered, “does a hot tub heat up faster with the jets on?”.

Having owned 4 hot tubs, this is what I found out:

Leaving the jets on while the water heats up does speed up the process in a 220v hot tub, as it ensures all of the water gets continuously circulated through the heater, leaving no pockets of cold water. However, 100v plug-and-play hot tubs do not allow the heater & pump to run simultaneously.

But that’s just a quick snapshot. Also, because most jets and water features time out, it is important to restart them periodically during the heating process.

And many tubs have multiple blowers or pumps, which don’t always produce the same result.

So in this article, we’ll get into all the details, as well as cover a few other ninja tips to get that water hotter faster! And some of the tips will apply even if you have a 110v hot tub!

To find out what I do to get my hot tub to 100°F in double-quick time, read on.

Should jets be on when heating the hot tub?

You don’t have to turn on the jets to heat up the water in a hot tub, but it greatly improves the speed at which the hot tub water temperature reaches its set point. The heater will naturally turn on anytime the water temperature is below the set temp on the topside panel.

Jets heating faster happens for two reasons.

First of all, the friction caused by the water being forced through the pipes at speed increases the temperature and clears any cold air bubbles locked in there.

Secondly, the movement of water throughout the hot tub eliminates cold pockets in the corners. 

There is one other thing to note about turning the jets on to speed up the heating process. If you have a Plug’n’Play type that runs off 110v, the chances are you can’t run the heater and jets simultaneously.

This includes both inflatable hot tubs and hard-sided hot tubs that just plug into a standard wall outlet.

This is because the ground-fault circuit interrupter (GFCI) will cut out if you have them both running. To overcome this, manufacturers make it so that the heater switches off when you turn the jets on full.

In this case, the best you can do is turn off the jets and allow the pump to draw the water through, heating it slowly. Alternatively, you can look at other ways to heat your hot tub quicker – see below for more details.

How can I make my hot tub heat up faster?

A hot tub will heat up faster with the lid firmly in place, even if it’s hot outside. For 220v hot tubs, turn on every jet and water feature for maximum circulation. A more permanent solution for budget hot tubs is to upgrade the heater to a more powerful one.

Those of us who have owned a hot tub for some time know that it can take hours to heat up. And it can be frustrating when you’ve just refilled it and want to get in.

I discussed whether using hot water to fill your tub was a good idea in this recent article. After all, it sounds like a great idea, in theory, to attach a garden hose to your hot water heater. But is it?

Just click that link to read it on my site.

If you want a more permanent solution, consider upgrading your heater from a 4kW to a 6kW. This will give you a 50% increase in power, reducing the amount of time it takes to get your water up to 100° by 25%.

If it took 8 hours with a 4kW heater, it would take 6 hours with a 6kW heater.

How long does it take a hot tub to heat up 5 degrees, and will jets speed that up?

An average hot tub with a 4kW heater will raise the water temperature by 5°  in under one hour. Turning on the jets will improve that time by about 10 minutes.

But the water temperature you’re starting with can vary a lot.

I measured mine, and it came in at 72 degrees during fall. But at other colder times of the year or colder parts of the country, that could easily drop to 65° or even lower.

If you start at 70° F (21° C) and want to get it to 100° F (38° C), without jets, that could take 6 hours. By comparison, turning on the jets can reduce that by 1 hour; not insignificant!

I went into some detail discussing the other factors that affect the length of time it takes a hot tub to reach 100° in a recent article. I even got into the one thing you are probably doing now, which could be slowing you down.

Just click on the link to read it here on my website.

If the jets are turned off, the pump will continue to push water across the heater element, and the heated water will pass through the jet nozzle at a low velocity, but it won’t mix with air to produce bubbles.

This circulation is essential to keep the water clean and to allow the chemicals to do their job.

If the jets are turned on, the process suddenly speeds up. Air is introduced at the nozzle, and the water is dispersed quickly, heating every part of the hot tub, so there are no cold spots.

Do hot tub jets make the water go through the heater?

All hot tubs have at least one pump, which pulls the water through the heater tube.  However, some hot tubs also have a blower for additional bubbles, which simply blows air into the water and does not cause it to be circulated through the heater.

But to answer this more fully, I need to explain a little bit about how the jets in your hot tub work.

The hot tub pump draws water into the filter through the suction line, and from there, it passes over the heating elements. The water then enters the pipeline feeding the jets, usually via a manifold hub or a series of individual manifolds.

The pipe at each jet reduces in size, which increases the pressure forcing the water through the wider jet nozzle where it mixes with air to produce bubbles. This is known as the Venturi Effect, where the water’s velocity increases as the static pressure decreases.

So, it is the pump that does the hard work.

The jets are just the end-part of the sequence. The visible part that you can adjust to suit your needs, and when the jets are turned off, the water is released slowly into the hot tub to keep the circulation going.

If you decide to turn off your hot tub between usage – which I would not recommend unless you are going away or don’t intend to use it for a while – it will take a lot longer to raise the temperature to 100° F (38° C).

So you need to bear this in mind before shutting down.

Should I leave the cover off my hot tub if the jets are on?

A hot tub will heat faster with the cover on. However, running the jets while the cover is on can, over time, damage the fabric on the underside. So only use the jets with the cover on 3-4 times per year every time freshwater gets heated following draining.

Whenever your hot tub is not in use, you should keep the cover on.  This not only keeps out animals and toddlers who may be interested to see what’s in there, but it will also keep it clean and free from debris and insects.

But the main reason you should leave your cover on is to reduce heat loss.

It takes a long time to heat the water to the optimum running temperature of around 100°, as we have discussed, so we don’t want it dropping too much in between sessions.

And always leave the cover off, for about 20 minutes, when you adjust the chemicals in your hot tub.

After all, when you add chemicals, with the exception of when you’re trying to lower pH, always turn the jets on. Turning on the jets right after adding chlorine, bromine, or alkalinity or pH adjusters help circulate the chemicals into the water evenly and faster.

But jets do raise the pH, so the lone exception is to not turn on the jets if you want to lower pH.

Did I cover all you wanted to know about leaving the jets on to make your hot tub heat up faster?

Leaving the jets running while heating up the water is definitely a good thing to do, so long as you can do both simultaneously. If you can’t or don’t want to do that, you can still speed up the process by pre-heating the water.

Jets are an essential part of the process – they mix air with the hot water coming through the pipes, and that is what gives you that spa experience, so you need to look after them by ensuring good water chemistry.

Remember also the importance of good insulation to reduce heat loss between uses, so you are only raising the temperature by a few degrees every time.

If there is anything I didn’t cover that you would like to know, drop me a line or just click on the links to see previous posts on my site.

Photo which requires attribution:

Jacuzzi by Grant Guarino is licensed under CC2.0 and was cropped, stretched, edited, and had a text and graphic overlay added

Jeff Campbell