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Hot Tub Air Source Heat Pumps: The Comprehensive Guide for 2023

How does an air source heat pump work?

An air source heat pump absorbs heat from the air and uses a compressor to raise its temperature to a higher level, then transfers the heat to a hot water cylinder. Here’s how it works:


The heat pump’s fan draws in air into a pipe filled with refrigerant, which is heated and transformed into a gas.

The gas is then compressed using an electric pump, significantly increasing its temperature. It then enters a heat exchanger, where the heat is transferred to the hot water cylinder.

Afterwards, the refrigerant gas inside the heat pump cools and turns back into a liquid as it passes through a pressure valve, starting the process again.

The warmer the weather, the more efficient an air source heat pump becomes as it can absorb more heat from the air. However, heat pumps can still operate at temperatures as low as -15°C—it just takes them longer to heat your hot water cylinder.


The efficiency of an air source heat pump is around 350%, significantly higher than standard hot water cylinder heaters.


This can result in significant savings in heating costs. For example, the cost of heating a home and/or hot water cylinder using a standard electric heater is around 20.06 pence per kilowatt-hour, whereas the cost with a typical air source heat pump is only 5.73 pence per kilowatt-hour. In initial tests with a hot water cylinder, we found that the cost of heating the cylinder per day per cycle was £2, but after adding the heat pump, the cost reduced to £1 per day.


When it comes to the electricity costs of the hot water cylinder, an air source heat pump can typically save you between £300 and £500 per year in operating costs. The higher the energy costs, the greater the savings.


How much does a hot tub heat pump cost?

While air source heat pumps can significantly reduce your energy costs, they are not cheap. Purchasing and installing an on/off heat pump from a cheaper brand will cost you around £1,500. We recommend opting for a well-known brand’s 12kW inverter model, which has an installation cost of around £3,500.


How fast does the heat pump heat the hot tub?

The speed at which a heat pump heats a hot tub depends on several factors.


Firstly, each heat pump has a Coefficient of Performance (COP) rating. If a heat pump has a COP of 4, it means that for every kilowatt of electricity it uses, it produces 4 kilowatts of actual heat. Therefore, the higher the COP of a heat pump, the faster it will heat the hot tub (and the lower the operating costs).


The ambient air temperature also plays a significant role in the speed at which the heat pump heats the hot tub. The less heat there is in the ambient air, the more challenging it is for the heat pump to reach a certain temperature. Therefore, you can expect the heat pump to heat the hot tub slower in winter compared to summer and with higher operating costs (still more cost-effective than standard heaters even in winter).


Lastly, the insulation effectiveness of the hot tub affects its heating speed. The more heat the hot tub leaks, the slower it will heat up (and the higher the cost of maintaining hot water).

heat pump installation

What is the payback period for a hot tub heat pump?

Since air source heat pumps cost several thousand pounds and can save you approximately £500 per year in energy costs, you can typically recoup the cost within two to three years. After that, it is expected to save you thousands of pounds in hot tub heating costs over the years.


Are there different types of air source heat pumps?

There are primarily two types of hot tub heat pumps: on/off heat pumps and inverter heat pumps.


As the name suggests, on/off models have two modes: on and off. These models are often cheaper but are not as energy-efficient since they do not have variable speeds.


On the other hand, inverter models are powered by variable-speed fans. Many high-end inverter heat pumps also feature smart technology that can monitor the ambient air temperature and adjust fan speed for optimal heat pump efficiency. These models often have higher upfront costs but lower operating costs.


Is the air source heat pump suitable for the UK climate?

While we may consider the UK weather to be not the best, our climate is relatively mild compared to many other countries.


Our average temperatures range from around 9 to 12°C, which is well within the working parameters of a good air source heat pump. In fact, some heat pumps can heat water at temperatures as low as -15°C.


As long as you ensure you purchase a heat pump capable of withstanding low temperatures, heating your hot tub should not be an issue.


Most reputable brands of air source heat pumps can operate at temperatures as low as -5°C, but be cautious of models designed specifically for summer use, which may only operate at temperatures as low as 10°C.


Can the heat pump work in winter—how low can the temperature go?

Quality air source heat pumps for hot tubs can heat your hot tub even at temperatures as low as -15°C. This means they are fully capable of handling UK winters and can continue to operate even in the harshest winter weather.


Just make sure you get a model specified to handle these temperatures and check the specifications of the particular model you’re interested in to ensure it can handle those temperatures.


How loud is the air source heat pump?

In general, air source heat pumps are not very loud. Good models will only produce a low humming sound.


There are legal decibel limits for every air source heat pump, so you will be able to know how loud the model you have in mind is before installation.


What does the hot tub need to be compatible with the heat pump?

When installing an air source heat pump for a hot tub, the first requirement is adequate space—enough to accommodate the heat pump itself and allow for good airflow.


You will also need a hot tub with a cabinet spacious enough to accommodate the additional piping required to connect it to the heat pump. A reputable hot tub dealer will be able to guide you in the right direction here. Some hot tubs are even “heat pump ready,” so keep an eye out for hot tubs that can save you on expenses.


Another essential requirement for a hot tub looking to install a heat pump is good water flow. Hot tubs with very low-flow systems and minimal water turnover will not provide optimal heat exchange with the heat pump’s heat exchanger. Therefore, the higher the water turnover rate of the hot tub, the more compatible it is with an air source heat pump.


You will also need to provide power to the heat pump. Some heat pumps can have the power supply of the hot tub itself turned off, but most heat pumps require a power supply with a minimum of 13 amps (or higher).

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Shenling will be the best solution of how to use a heat pump in winter

Where can a hot tub heat pump be installed?

Most heat pumps can be installed up to five meters away from the hot tub. However, the closer the air source heat pump is to the hot tub, the less heat loss there will be in the piping, resulting in higher operational efficiency for the hot tub.


How much clearance does the heat pump need?

Most hot tub heat pumps require a clearance of two to three meters at the back for exhaust and a clearance of 60 centimeters to two meters at the front to allow sufficient space for air intake.


Therefore, be sure to check the manufacturer’s specifications before purchase to ensure you have enough space to accommodate the model you’re interested in.


How big is a hot tub heat pump?

A typical 12kW air source heat pump for a hot tub has a length of around one meter, a depth of approximately 500 centimeters, and a height of around 700 centimeters. So they can be quite sizable. However, the larger the heat pump, the greater the surface area, and the more money it will save you.


What size or output heat pump do you need?

For residential use, heat pumps with output powers ranging from 5kW to 12kW should suffice. However, the larger the heat pump, the quicker you will see a return on your investment.


If you’re looking for a heat pump for a holiday home and quick heating time is a priority, then the minimum model you should consider is a 12kW model, with the maximum output power potentially reaching 17kW.


Does installing a heat pump void the hot tub’s warranty?

If you install an air source heat pump into a hot tub without manufacturer approval, your warranty will be voided.


However, an excellent hot tub dealer with connections within the brand may be worthwhile here, as they can often get authorization to retrofit an air source heat pump to a specific model without voiding the warranty.


How long do heat pumps last?

Like any product you purchase, the lifespan of a heat pump depends on the quality of the model you invest in.


Inverter models often come with a 10-year warranty for the inverter itself and a five-year warranty for most components, while some cheaper on/off models may only have a 12-month warranty.


Do heat pumps degrade over time?

As long as your heat pump receives annual maintenance, its performance will not decline.


The cost of an annual heat pump service typically ranges from £50 to £90, and it prevents performance degradation in two significant ways.


Firstly, all debris will be sucked out from the heat exchanger, ensuring it operates as efficiently as possible. Secondly, the gas inside the heat pump will be recharged to keep it exchanging heat.


How much electricity does a heat pump consume?

Heat pumps are an excellent alternative to electricity, and a heat pump running at full load averages around 2.3 kilowatts of electricity consumption per hour.


Premium air source heat pumps use only approximately 0.7 kW of power per heating cycle for a hot tub. In comparison, a standard electric heater consumes around 3 kW of power during a heating cycle, more than three times as much.


Does the heat pump bypass or replace the built-in hot tub heater?

The heat pump can replace or supplement the standard hot tub heater.


For holiday home owners, having both a heat pump and an electric heater provides the best of both worlds—shorter hot tub heating time and lower costs to maintain that temperature. However, you will need upfront funds to invest in retrofitting the heat pump and its space for your hot tub.


For residential use, the hot tub’s electric heater is almost always disconnected and replaced by the heat pump.


Do I control the hot tub’s temperature through the hot tub control panel or the heat pump?

Some heat pump manufacturers (such as Gecko) are designed to integrate into the hot tub’s heating system and are controlled through the spa controller.


However, this is the exception rather than the rule, and if you install a heat pump, you will be able to control the hot tub’s temperature through the heat pump.


Is a hot tub heat pump right for you?

Over the years, a hot tub heat pump can save you a significant amount of money. However, before applying for a credit card, ask yourself a few questions:


How long do you plan to stay in your current home?
If you move homes before the heat pump’s payback period is over, the purchase will leave you at a loss.


Is this the best return on investment for the money you’re spending?

Most of us don’t have thousands of pounds lying around.


Therefore, it’s important to crunch the numbers and calculate whether an air source heat pump for your hot tub will have the most significant impact on your household bills.


For beginners, improving the hot tub’s insulation performance or investing in a new cover might save you more money, depending on its current condition.


If you’re considering purchasing a hot tub, do your due diligence and make sure you choose a well-insulated hot tub. Adding a heat pump to a well-insulated hot tub will ensure you don’t lose heat from the tub quickly. That money could also be put towards insulating your home, installing energy-efficient doors and windows, or upgrading your car to a more fuel-efficient model.


So be sure to calculate which home improvement will save you the most money and have the quickest return on investment before pulling the trigger. Installing a hot tub heat pump is likely to be at the top of the list since it can provide such significant savings each year, but it all depends on your circumstances, so do your homework before you take the plunge.


Do you have space?

Since the heat pump is a separate device located next to the hot tub, you will need to provide space for it.


Technically, you may have enough space, but in reality, it may make your outdoor space feel cramped or uncomfortable to access and exit the hot tub.


Do you like how they look?

While you can find some heat pumps that have a sleek appearance, it cannot be ignored that you will have an air conditioning-like unit next to your home spa.


If you have carefully designed your space or sunk your hot tub, this may disrupt the aesthetics you desire, so you may choose to forego the savings to pursue aesthetics.


Pros and cons of air source hot tub heat pumps

In summary, the advantages of air source hot tub heat pumps are:

  • Savings of around £500 per year in energy costs by reducing operating costs
  • Reduction of your carbon footprint by improving energy efficiency
  • Long-term savings on hot tub heating costs


The disadvantages are:

  • Significant upfront costs
  • Occupying additional space in your garden (and not known for their aesthetics)
  • Potentially longer heating times in winter compared to standard heaters


Are hot tub heat pumps suitable for holiday homes?

Combining a heat pump with an electric heater can provide a win-win experience for holiday home owners—shorter hot tub heating times and lower costs to maintain the desired temperature. However, you need the upfront capital to invest in retrofitting the heat pump and its space for your spa.


Final thoughts

An air source heat pump can save you hundreds of pounds per year on energy costs and recoup the cost several times over the time you own it.


For hot tub owners with the upfront cash and space, investing in a heat pump for a hot tub can be a highly effective way to reduce energy usage and carbon footprint while increasing savings in an era of rising energy costs.

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