The complete guide to hot tub heaters

Posted by Nick Clamp in Buying on 5th January 2023

A spa’s heater literally puts the “hot” in hot tub. So, it’s well worth knowing a bit about how to get yours firing on all cylinders. 

Read on to learn everything you need to know about this essential hot tub component, including how to extend its lifespan – and help it get your spa up to temperature faster. 

The different types of hot tub heaters

The vast majority of hot tubs come with an electric heater as standard. These are powered by the electricity that comes into your spa through your 13 or 36 amp power supply

But, if you’re looking for a more energy-efficient way to heat your hot tub, have a hot tub heat pump installed. These clever heaters draw heat from the air, compress it to a higher temperature, then transfer that heat to your hot tub. 

Since an air source heat pump is around three times more efficient than a standard electric heater, making the switch could shave hundreds of pounds off your hot tub running costs each year. Just beware that a heat pump will take a bit longer to heat your spa up. Plus, you’ll need the room for one, since it’s a freestanding unit that sits alongside your hot tub rather than fitting inside it like an electric heater.

Signs your hot tub heater might need replacing

You can expect to get around eight years of good use out of a standard hot tub heater, so you’ll more than likely have to replace yours before you replace your spa. Here are some common signs your heater might need replacing:

Your hot tub isn’t heating up at all

If your spa isn’t warming up at all then it might mean your heater has gone the journey. But it’s well worth troubleshooting some alternatives before you buy a replacement as it could just as easily be caused by a few other issues.

First, check that your spa is definitely getting power. If it is, take a look at your hot tub’s control panel. If the display is showing “FLO”, that means the water isn’t flowing through the plumbing system properly, which means it isn’t passing your heater and warming up. 

Here’s how to fix this problem:

If “FLO” is still displaying on your spa’s control panel after you’ve run through this process then it’s time to call a professional, as there might be a deeper issue (such as air bubbles in the heater chamber) that you won’t be able to fix by yourself.

Your hot tub is getting warm, but not hot

If your hot tub is more of a warm tub – especially in winter – then your heater might not be big enough for the job. If you’ve gone for an inflatable spa or a cheap grey import then its heater might just not be powerful enough to get your hot tub up to temperature when the ambient temperature drops. 

Unfortunately, you can’t just buy a more powerful heater for an underpowered home spa. Fit a 5kW heater in a model designed for a 1kW one and you’ll overload its circuits. 

You can follow the tips we’ve outlined below to help an underpowered hot tub get hotter. But you might have to invest in an upgrade if you want to enjoy winter soaks (or winterise your hot tub every year if you’re not fussed about soaking in the colder months).

© Arctic Spas

Your hot tub’s temperature fluctuates 

If your hot tub’s temperature regularly plummets to freezing cold and then soars to boiling hot, its temperature sensor, thermostat, or heat sensors might be on the fritz. You’ll need to call out a professional to take a look into this problem for you.

How to make your hot tub heater last longer

You can extend your hot tub heater’s lifespan by a good few years by doing a few simple things that will keep it in top knick. 

So, be sure to:

  • Keep your spa’s water balanced, as it will start eroding your heater’s element as soon as its pH creeps below 7.2 or above 7.8.
  • Flush all air out of your hot tub’s plumbing system after every clean, as trapped air can cause havoc to your heater.
  • Regularly clean and change your hot tub’s filters, as filters full of dirt and debris will reduce water flow which could burn your heater out. 
  • Get your hot tub serviced every year, as a technician will be able to spot any potential problems and nip them in the bud before they develop into a heater-killing headache. 
© Vortex Spas

How can I make my hot tub heat up faster?

There’s plenty you can do to make sure your hot tub gets up to temperature as fast as possible, no matter what kind of heater it has.

Here are a few simple things you can do to give your heater a helping hand:

Invest in a quality cover

Your home spa loses about 60% of its heat through the surface of its water. A quality cover can therefore make a huge difference to how fast it heats up – as well as how much it costs to run. 

© Caldera Spas

Look out for a hot tub cover that’s:

  • Filled with high-density, heat-sealed polyurethane foam
  • Has a rubber seal that creates an airtight seal that traps heat in
  • Is made from marine-grade vinyl that’s been treated against mildew
  • Is thicker in the middle and tapers towards the edges so rain and snow run off
  • Has a vinyl skirt that offers an extra layer of insulation (and hides the rubber seal)

An easy way to test whether a hot tub cover is up to scratch is to place your hand on the top of it. If the top of the cover is room temperature, that means it’s trapping in heat as efficiently as possible.

Get insulated

Your hot tub will heat up as fast as possible if it’s filled with quality insulation

If it’s within your budget, we’d strongly recommend you opt for a home spa that’s been fully insulated with high-quality foam. Partially foamed hot tubs are a good second choice if you’re on a tight budget – just be aware your monthly energy bills will be higher, so this might actually work out as more expensive in the long run. 

Whatever you do, don’t buy a cheap grey import that’s only insulated by a thermal wrap – a common way unscrupulous manufacturers cut their production costs. Sticking to WhatSpa? recommended brands is an easy way to avoid being burned on a dodgy spa that’s insulation isn’t up to scratch.

Get your spa regularly serviced

Broken or worn out pumps, filters, and jets are going to take a lot longer to heat your hot tub up. So, be sure to follow a proper hot tub maintenance routine and regularly get your hot tub serviced to help make sure its components are always working as effectively as possible.

© Villeroy & Boch

Embrace landscaping

It’s well worth putting a bit of thought into your hot tub landscaping. Plonk your spa in a shady wind trap and it will take a lot longer to heat up than if you place it somewhere it’s protected from the elements. 

If you have the space, install your hot tub in a natural alcove or block the worst of the weather by installing a windscreen, planting a hedge, or building hot tub housing around it to act as a buffer from the wind (and add some privacy to your soaks).

© Hot Tub House Yorkshire

Turn the jets on

A simple way to get your hot tub up to temperature faster that doesn’t cost you a penny is to simply turn on your hot tub’s jets. This will help circulate the heat around the whole body of water and prevent cold patches from forming.

© Coast Spas HQ

Use a thermal spa blanket

A thermal spa blanket is a simple foam sheet that floats on your hot tub’s surface and helps trap the heat in. Place one on your hot tub’s water whenever you’re not using it to help bring it up to temperature as quickly as possible. 

The final word

Stick to the tips we’ve outlined here to troubleshoot any problems you might have with your hot tub’s heater – as well as make sure it gets your hot tub up to temperature quickly and lasts as long as possible.

And pick up your free copy of WhatSpa? magazine for more expert advice on buying, installing, and maintaining a hot tub – as well as our latest hot tub reviews.

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About the author

Nick Clamp

I am the Editor-in-Chief at WhatSpa? Media Group and have been actively involved in the hot tub and swim spa industry for over 20 years. I fell in love with hot tubbing in 2002 and since then have dedicated my career to helping millions of hot tub buyers to make more informed choices when navigating their buying journey.

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