The Ultimate Guide to Hot Tub Heaters and All Things Heat Related

Hot Tub Heater

If you are a new Hot Tub owner or a seasoned Hot Tub pro, heating a Hot Tub is probably, I’ll rephrase that, definitely, going to be a priority. A Hot Tub with no heat is, after all, is just a tub!

How well you can heat it depends on the condition, efficiency, power, environment, insulation and location of your Hot Tub.

The best things come to those who wait” is the saying, but we certainly don’t want to be waiting forever for our tubs to heat up. Each Hot Tub is different but with the correct Hot Tub heater and regular maintenance and perhaps some strategic upgrades, you can find ways to get your tub hot and bubbling in no time!

Wait, I Can Replace My Hot Tub Heater?

Yes! While all Hot Tubs come with a heater installed, it is a feature that can be replaced or upgraded as required. It would be ludicrous if every time the heater died, you had to get a new Hot Tub! Usually this is found in modern hot tubs as part of the Spa Pack which you can of course upgrade or replace.

The heater that comes with your Hot Tub is kind of like the stock stereo that comes with a new car. It works and it sounds ok but you really should upgrade it if you want to bang out some serious tunes!

Hot Tub heater upgrades can mean that your water heats up faster. This can be achieved by increasing the size or power of the heater. Whether the heater itself is more efficient or is using less energy and is therefore costing you less money is open to debate and there are a lot of external factors at play. We’ll cover some of them in the article. However, as a general rule of thumb, the higher the Kilo Watt (KW) rating on the heater the more powerful it is and the faster it will heat up your tub. Think of it like a domestic heater. 1KW doesn’t give off as much head as a 3KW fire…Bigger the “fire” faster the tub heats.

Factors That Can Affect Hot Tub Heating Efficiency

Depending on several factors, some internal, some external, your Hot Tub could heat quicker or slower. These include;

  • Ambient temperature, or the temperature outside and around where your Hot Tub is located
  • Hot Tub cover placement (on/off, secure/loose and if course its condition, old/new/letting in water, all these kinds of things)
  • Condition of your Hot Tub’s hardware

Ambient Temperature

The warmer the water and the surrounding air, the less time it will take to heat your Hot Tub to the correct temperature. What’s the appropriate temperature? Health experts suggest for adults that 104 ° F (40 ° C) is the upper limit for the temperature of the Hot Tub. Somewhere between 100 ° F (38 ° C) and 102 ° F (39 ° C), you will probably find your Hot Tub more comfortable. This is the level that I set my own tub at.

Let’s assume it’s 76 ° F (24 ° C) outside and your water is at the same temperature. It will take 4 to 8 hours to heat your Hot Tub to 100 ° F (38 ° C). It will take 8 to 16 hours to hit 100 ° F (38 ° C) if, on the other hand it’s a chilly 52 ° F (11 ° C) outside and your water is the same temperature.

Pro Tip: Monitor the temperature with a floating Hot Tub thermometer as it rises. This is to make sure the thermometer built into your Hot Tub control panel works correctly. Then you can compare the readings with your system temperature and check for accuracy.

Cover Placement

Leaving the Hot Tub cover on as you wait is another way to speed up the heating of your Hot Tub. Heat loss into the air is where most of the heat goes from your tub. Leaving the cover in place traps the heat and assists with the water temperature increase.

Pro Tip: An old cover will reduce efficiency and harbor all kinds of microbes and funky grime. If yours has seen better days, consider replacing it to boost not only the heating efficiency of your Hot Tub but the overall health and safety of your spa too. Another tip here, a cover that is heavy as it has taken on water has lost a great deal of its thermal properties once it is wet inside. Time for a change when this happens it will save you money in the long run.

How to Heat a Hot Tub Even More Efficiently

With a couple of changes and enhancements to the surrounding area of the Hot Tub, you can actually improve the thermal capacity believe it or not!


When you design your Hot Tub setup, it can be all too tempting to forget the value of not only beautiful but practical landscaping. In addition to holding the heat in, blocking the wind and weather from your Hot Tub will help keep the cold out. In turn, this will allow you to heat the tub quicker and ultimately save you money. Who thought a few strategically placed plants were going to help the thermal dynamics of your tub?

Evaporation and cooling can be increased by wind making your Hot Tub work harder to achieve the right temperature, and sustaining it once it is reached. Planting trees in your yard will significantly reduce the wind. By planting shrubs, you can also make a smaller, more localized windbreak around your Hot Tub area. Special screens around your Hot Tub can also be mounted to block the wind and help keep your Hot Tub warmer for longer. These panels, like landscaping, help make your Hot Tub more private too.

Improve Your Hot Tub’s Insulation

Although the majority of the heat is lost through the open surface of the water from your Hot Tub when the cover is off, you can also lose some heat due to bad insulation in the cabinet.

Adding insulation will help keep cold air out by bulking up the thermal “blanket”, making it easier to heat your Hot Tub. It will help keep it warm as well, so if you haven’t used it in a few days, you won’t need as much time or energy to get your Hot Tub up to the right temperature.

To boost its insulation capacity, you can add wall or attic insulation on the inside of your Hot Tub cabinet panels. Or, if you’re more of a DIYer, you can build a surrounding cabinet and fill it with insulation, essentially a cabinet for your cabinet. This may seem somewhat of an overkill but done in a good way will save you some serious cash.

Bulk Up the Cover

We’ve already mentioned that most of the heat escapes upwards which is why a well maintained and fitted cover is needed. If you are still struggling, you can bulk up the cover. No, we’re not talking about adding loft insulation or anything like that, we’re talking about adding a floating blanket to the surface of the tub. Not one off your bed FYI! What the heated floating blankets do is add an additional layer of insulation and assist in keeping the heat in the water rather than letting it escape.

You are though adding a second heat source which will cost you in the wallet!

Should You Leave Your Hot Tub Running?

I see this question on a weekly basis on the Facebook Forums that I follow related to Hot Tubs. The response to this question depends on how you use your Hot Tub and when you use it.

If you live in a colder environment and you want to use your Hot Tub a few days a week, by having it run at a lower temperature during the period you don’t use it and turning the Hot Tub heater up to temperature when you do need it, can save time and money. This is actually what I do with my own tub. I never turn it off unless I am going on vacation. During the week when I am not using it I set it to 33C and then turn it up to 39C Friday-Sunday when it is in actual use.

On the other hand, if your area’s climate is milder and you use your Hot Tub only occasionally, it makes sense to shut it down between uses.

You’ll have a different decision to make if you have sub-zero winters where you live and if your Hot Tub is outdoors. Freezing temperatures and snowfall are going to impact heat up times so you need to be aware of this. Letting it cool down too much is not a good idea if you are looking to use the tub any time soon.

We do have a blog post on how to Winterize your tub if you are not a lover of the cold air and freezing temperatures – personally, this is the best time of year for my tub as it is prolonging the use of the garden!

How to Troubleshoot a Hot Tub Heater

There is nothing worse than getting into a cold Hot Tub. If your Hot Tub is not sufficiently heated, one of three symptoms is likely;

The Hot Tub Isn’t Staying Hot

If your Hot Tub heats up without a problem, but then just tends to fizzle out and cool like a normal bath, the filter is the first thing to check to ensure that it is not clogged. Clear it out if you find debris and then give the filter a thorough cleaning.

If the problem is not with the filter, check the thermostat and heat sensors. Often electrical components will fail or go bad and they will need to be replaced. Changing the heat sensors is usually a quick and inexpensive fix on modern hot tub control packs.

Finally, check the circulation of the Hot Tub. If the pipes are clogged then the water may not flow correctly. Once it is heated, it will begin to cool down gradually as the hot water is not getting replenished. You may need to drain and clean the Hot Tub if this is the case and to clear the plumbing blockage and use some form of a line flush product.

The Hot Tub Temperature Fluctuates

Identifying this can be a difficult problem because it can trick you into believing that nothing is wrong.

Turn the Hot Tub on and jump into warm water. Five minutes later, you’re shivering because even though you didn’t press any buttons, the temperature has fallen.

But then it heats up again so you think it was nothing and go on soaking until the water gets so hot that you feel like you’re stewing on the menu for dinner.

Fluctuating temperatures are caused by a temperature sensor that has begun to die. It could be the thermostat also if the sensor is in good working order. Whichever of the three things is the problem, the respective parts are going to have to be replaced.

The Hot Tub Isn’t Heating at All

Turn your Hot Tub on, wait for it to heat up for a little bit, but then you still have ice-cold water or at least room-temperature water. Yikes! Believe it or not, this can be triggered by a low flow rate from your Hot Tub pump. You will have to replace the pump if that’s the issue.

A weak heating element can also be responsible for the absence of heat. There’s no point trying to repair the element itself when it fails; just replace it.  Luckily, all these heating parts are easy to replace and are not too expensive.

Understanding the Heating Element Assembly

The heating element in traditional Hot Tubs is found inside the heater assembly housing. This housing exchanges the heat produced by the heating element as it passes through the tube with the water.

Sensors such as a thermostat are often used by some heating assemblies to regulate the temperature and a high limit switch to prevent the water from being too hot. Makes sense I guess.

How to Replace the Heating Element

It is easier than you think to replace this part in your Hot Tub heater.

Important: Disconnect all the power leading to it before you begin any sort of work on your Hot Tub.

  1. Locate the heating element inside your Hot Tub cabinet.
  2. Disconnect the electrical wires. Usually, this is connected to the Spa Control Pack.
  3. Remove the heating element. There are usually some external bolts that need to be removed in order to gain access to the element. On some models, the heating element is actually inside the Spa Pack.
  4. Replace with a new element and then reverse the steps to fit, secure and then test.

Maintain your Heating Element

Looking after your heater element can save you time and money in the long run. Here are a few pointers.

Keep the Water Balanced

Inside your Hot Tub, balanced water chemistry will help prevent corrosion and prolong the life of the heating element and the Hot Tub heater in general.

Keep Air Out of the System

Be sure to flush all the air out of the system after every maintenance session. Air in the lines will lead to the premature failure of the heating assembly.

Clean the Filter Regularly

Clogged filters can stop proper flow of water to the heater which can ultimately cause the heating assembly to burn out. Check your filter periodically and when needed, clean or replace it.

If in Doubt, get a Pro Out.

Don’t hesitate to contact a professional if any of this maintenance or repair work makes you nervous or you are unsure of what you are doing.

Water and electricity don’t mix, so it’s safer to have a pro come in than to put yourself in danger if you’re not confident in your DIY skills.

No More Lukewarm Soaks for You!

Until we can breathe fire or have Infra Red eyes like the X Men, we will need to rely on Hot Tub heaters to get our tubs up to temperature.

The good news is, as long as you invest in good equipment, keep up with the maintenance of your Hot Tub, and fix issues as soon as they arise, you can keep your heater going and enjoy your Hot Tub for many years to come.

Happy Tubbin’

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi


Hi, Andi here. I own and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Today, I've helped over 1000 DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi

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