Installing an air source hot tub heat pump could shave hundreds of pounds off your hot tub running costs each year. Read our ultimate guide to find out how hot tub heat pumps work and whether one might be right for you.
How do air source heat pumps work?
An air source heat pump takes heat from the air, boosts it to a higher temperature using a compressor, and then transfers that heat to your hot tub. Here’s exactly how it works:
The heat pump’s fan draws air over tubes full of refrigerant, which is warmed up and turned into a gas.
This gas is then compressed using the electric pump, which significantly increases its temperature. Then it’s passed into a heat exchanger which transfers that heat to your hot tub.
The refrigerant gas inside the heat pump then cools and turns back into a liquid upon passing through the pressure valve, starting the process again.
The warmer the weather, the more efficiently an air source heat pump works, as it can take more heat from the air. But heat pumps still work in temperatures as low as -15°C – it just takes them longer to heat your hot tub up.
Is an air source heat pump worth purchasing for a hot tub?
Air source heat pumps have an efficiency rating of around 350% – significantly higher than standard hot tub heaters.
This can lead to some serious savings on heating costs. For example, it costs 20.06p per kWh to heat a home and/or hot tubs with standard electric heaters compared to just 5.73p per kWh with a typical air source heat pump. In initial tests with hot tubs we have seen hot tubs that were costing £2 per heat per day see that cost drop to £1 per day with a heat pump added.
When it comes to your hot tub’s electricity costs, it’s typical for an air source heat pump to save you in the region of £300 to £500 per year in reduced running costs. And the higher energy costs rise, the bigger those savings become.
How much does a hot tub heat pump cost?
An air source heat pump will seriously slash your energy bills, but they’re not cheap. Buying and fitting an on/off heat pump from a cheaper brand will cost you around £1,500. A 12kW inverter model from a reputable brand – which is what we’d recommend you go with – will cost around £3,500 fitted.
How quickly do heat pumps heat the water?
How quickly your heat pump gets your hot tub up to temperature will depend on a few different things.
Firstly, every heat pump is rated with a COP – a “coefficient of performance”. If a heat pump has a COP of four, that means it produces four kilowatts of actual heat for every kilowatt of electricity it uses. So, the higher your heat pump’s COP, the faster it will heat up your hot tub (and the cheaper it will be to run).
The ambient air temperature also plays a big part in how quickly a heat pump will heat up your spa. The less ambient heat that’s in the air, the harder a heat pump has to work to get up to temperature. So, you can expect your heat pump to heat your hot tub up slower – and cost more to run – during winter than in summer (while still being more cost-effective than a standard heater, even in winter).
Last but not least, how well insulated your hot tub is will play a big part in how fast it gets up to temperature. The more heat your hot tub leaks, the slower it will heat up (and the more expensive it will be to keep it hot).
What’s the payback period of a hot tub heat pump?
Since an air source heat pump costs a few thousand pounds and typically shaves around £500 off your energy bills a year, they usually pay for themselves after two or three years. After that, expect it to save you thousands of pounds over the years on the cost of heating your hot tub.
Are there different types of air source heat pumps?
There are two main kinds of hot tub heat pumps: those that use on/off technology and those that use inverter technology.
As the name suggests, on/off models have two modes: on and off. These tend to be cheaper models, but because they don’t have variable speeds, they aren’t the most energy efficient.
Inverter models, on the other hand, are powered by a variable-speed fan. A lot of top-end inverter heat pumps have smart tech within them that checks the ambient air temperature and adjusts the fan speed to get the best efficiency out of the heat pump. These models, therefore, tend to cost more upfront but cost less to run.
While we think of ourselves as having lousy weather here in the UK, compared to a lot of other countries we have quite a mild environment.
Our average temperatures are around 9 and 12°C, which is well within the working parameters of a good air source heat pump. In fact, some heat pumps can carry on heating water in temperatures as low as -15°C.
As long as you make sure to buy a heat pump that can handle cold temperatures it will have no problem heating up your spa.
Most air source heat pumps from good brands can operate down to -5°C, but look out for models that are only designed for summer use and actually only work down to 10°C.
Do heat pumps still work in winter – and down to what air temperature?
An air source heat pump from a good quality brand will heat your hot tub in temperatures as low as -15°C. That means they’re more than capable of handling our winters here in the UK and will continue working even in the worst of the winter weather.
Just be sure you’re getting a model specified to handle those temperatures. And check the specs of the model you’ve got your eyes on to make sure it goes down to those temperatures.
How much noise do air source heat pumps make?
As a rule, air source heat pumps aren’t noisy. A good model in good condition won’t make more than a low whirring sound.
Every air source heat pump requires a decibel rating by law. So, you’ll be able to see how loud the model you’ve got in mind is going to be before you have it installed.
What does a hot tub need to be compatible with a heat pump?
The first thing you need to fit an air source heat pump to your spa is space – enough to fit the heat pump itself and for it to generate good airflow.
You’ll also need a hot tub with a cabinet that’s spacious enough to accommodate the extra pipework that will need to be fitted to connect it to a heat pump. A good hot tub dealer will be able to point you in the right direction here. Some hot tubs are even built “heat pump ready”, so look out for those to save yourself an expense.
Another must-have for a hot tub you want to fit a heat pump to is good water flow. A hot tub with a very low-flow system with very few water turnovers isn’t going to give you a good exchange rate through a heat pump’s heat exchanger. So, the higher the water turnover rate through the spa, the more compatible it will be with an air source heat pump.
You’ll also need a power supply for your heat pump. Some heat pumps can be powered off the hot tub itself alone, however, most need electrical requirements of a 13amp (or higher) power supply.
Where can a hot tub heat pump be positioned?
Most heat pumps can be fitted a maximum of five metres away from your hot tub. But the closer your air source heat pump is to your spa, the less heat will be lost in the pipework, making the tub more efficient to run.
How much clearance does a heat pump need?
Most hot tub heat pumps need two or three metres of clearance at the rear for the exhaust and anywhere from 60cm to two metres at the front so it has enough room to pull air in.
So, be sure to check the manufacturer’s specifications before you buy to make sure you have enough room for the model you’ve got your eye on.
A 12kW air source heat pump will generally measure a metre in length by about 500cm in depth and 700cm in height. So they can be quite big. But, the bigger the heat pump, the bigger the surface area it will have and the more money it will save you.
What size or output heat pump will you need?
For domestic use, a heat pump with an output of anything from 5kW up to 12kW should do the trick. But the larger the heat pump, the quicker you’ll see a return on your investment.
If you’re looking for a heat pump for a holiday let and a fast heat-up time is your priority, a 12kW model would be the minimum you should be looking at, potentially up to one with a 17kW output.
Will having a heat pump fitted void my hot tub’s warranty?
If you fit an air source heat pump to your hot tub without the permission of the manufacturer it will void your warranty.
However, a good hot tub dealership with contacts within the brand can be worth its weight in gold here, as they can often get you authorisation to retrofit an air source heat pump to a model without voiding its warranty.
How long do heat pumps last?
Like everything you buy, how long your heat pump lasts depends on how good of a model you invest in.
Inverter models tend to have a ten-year warranty on the inverter itself and a five-year warranty on most parts, while some of the cheaper on/off models will just have a 12-month warranty.
Do heat pumps degrade over time?
As long as your heat pump is serviced every year, its performance won’t degrade.
An annual heat pump service, which will usually cost in the region of £50 to £90, will prevent its performance from degrading in two important ways.
First, any debris will be hoovered out of the heat exchange, making sure that’s running as effectively as possible. Secondly, the gases inside your heat pump will be recharged so they continue to exchange heat.
How much electricity do heat pumps consume?
Heat pumps are a great alternative to electricity, with the average heat pump running at full load consuming around 2.3Kw of electricity per hour.
A quality air source heat pump will only use around 0.7kW of power per hot tub heating cycle. By way of comparison, a standard electric heater will use around 3kW during a heating cycle – over three times more.
Do air source heat pumps bypass or replace the built-in hot tub heater?
A heat pump can either replace or supplement a standard hot tub heater.
Having both a heat pump and an electric heater can be incredibly useful for holiday lets, which need to empty, refill, and reheat their spa water between guests.
But for domestic use, the hot tub’s electric heater will almost always be disconnected and replaced by a heat pump.
Do I control the temperature of the hot tub from the spa control panel or from the heat pump?
Some heat pump manufacturers, like Gecko & Balboa, are designed to be fully integrated into your hot tub’s heat systems and controlled through spa controls.
With heat pumps from manufacturers other than the ones stated above, you’ll control the temperature of your hot tub from your heat pump if you have one installed.
A hot tub heat pump will save you plenty of money over the years. But there are a few questions you should ask yourself before you reach for your credit card:
How long are you planning on staying in your current house?
If you move home before you’re out of your heat pumps’ payback period then it’s a purchase that will leave you out of pocket.
Is it the biggest bang you can get for your buck?
Most of us don’t have a spare few thousand pounds lying around.
So, it’s important to run the numbers on whether an air source hot tub heat pump is going to have the biggest impact on your household bills.
For starters, improving your hot tub’s insulation or investing in a new cover might save you more than switching to a heat pump, depending on its current state.
If you’re looking to purchase a hot tub then do your due diligence and be sure to select a well-insulated hot tub. Adding a heat pump to an already well-insulated hot tub will ensure that you don’t quickly lose the heat that the hot tub has generated. And that money could also go on insulating your house, installing more energy-efficient windows or doors, or replacing your car with a more efficient model.
So, be sure to run the numbers on which home improvement will save you the most money and have the quickest payback period. Installing a hot tub heat pump is more than likely going to be near the top of that list since it can realise such big savings each year, but it all depends on your circumstances, so be sure to do your homework before you pull the trigger.
Do you have the room?
Since a heat pump is a separate unit that sits alongside your hot tub, you’ll need the space for it.
You might technically have the space for one, but in practice, it would make your outdoor space cramped or make it uncomfortable to get in and out of your spa.
Do you like how they look?
While you can get some smart-looking heat pumps, there’s no getting around the fact you’re going to have what essentially looks like an air-con unit sitting next to your home spa.
If you’ve meticulously landscaped your space or sunk your spa, this might spoil the look you’re going for, so you might choose to forgo the savings in favour of the aesthetics.
The pros and cons of an air source hot tub heat pump
In short, the pros of an air source hot tub heat pump are:
It can shave around £500 off your energy bills every year in reduced running costs
It will reduce your carbon footprint via increased energy efficiency.
The cons are:
The big upfront cost
It takes up extra space in your garden (and isn’t known for its style)
It can take longer to heat your spa up than a standard heater in winter
Is a hot tub heat pump right for a holiday let?
A heat pump in conjunction with an electric heater will give holiday let owners the best of both worlds – quick hot tub heat-up times, then low costs to maintain that temperature. However, you’ll need the upfront capital to invest in fitting a heat pump to your spa – and the space for it.
The final word
An air source heat pump can accrue hundreds of pounds in savings off your annual energy bills, paying for itself several times over in the time you’ll own it.
Investing in one can be an incredibly effective way for hot tub owners with the upfront cash – and the space – to slash both their energy usage and carbon footprint, and increase savings in the face of rising energy costs.
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I am the Content Writer and Marketing Officer at WhatSpa? Magazine. I have worked at WhatSpa? for over 8 years, and I recently graduated with Distinction from Northumbria University with a Master's degree in Occupational and Organizational Psychology.
My role at WhatSpa? is to ensure that all hot tub lovers can easily access the highest quality and most up-to-date content, news and information from within the UK wet leisure industry.