The Ultimate Guide to Air Source Heat Pumps for Hot Tubs

Air Source Heat Pumps for Hot Tubs are a great alternative to the traditional gas or electric heating system. They require no installation of new pipework and can be placed virtually anywhere in your yard. The drastic reduction of energy costs plus fast heat up times makes this type of heating source very desirable for the DIY Hot Tub Builder. In this blog post we are going to look at everything you need to know about Air Source Heat Pumps for your DIY Hot Tub.

What is an Air Source Heat Pump?

Air Source Heat Pump for Hot Tubs

Air Source Heat Pump for Hot Tubs

In terms of Air Source Heat Pumps for Hot Tubs (ASHP) is a device that transfers heat either to or from the water in your tub. Under the principles of vapor compression refrigeration, the ASHP uses a compressor and condenser to absorb heat either from the air if we are heating the hot tub, or from the water, if we are chilling the Hot Tub (to use as a plunge pool in the summer) and releases it in the opposite direction. So, if we are heating the Hot Tub, then heat absorbed from the air outside is transferred to the water inside of the tub. Conversely, if we are using the ASHP in the summer to chill the hot tub into a plunge pool, then heat is absorbed from the water and released into the air.

How does it work?

An air source heat pump works by pumping a refrigerant through the heat pump’s copper heat exchanger coils. The compressor and condenser are used to change states of the refrigerant between cooler liquid and warmer gases. In heating mode, the liquid refrigerant boils as it passes through the heat exchanger coil.

Heat from the air that has previously been absorbed and stored in the refrigerant, is retained and carried within the refrigerant as it evaporates into a gas. The gas is then compressed using the electric pump, which increases the temperature of the gas through compression.

The gas passes through a pressure valve into the coil and the refrigerant gas is condensed back to a liquid and transfers the heat into the heating element which in turn, heats the water in your Hot Tub as it is pumped through the unit.

What are the Advantages of Air Source Heat Pumps?

Air Source Heat Pumps for Hot Tubs are one of the most efficient heating systems available. They can provide up to three times more heat than standard heating options, and they’re incredibly energy-efficient. This means that they are cheaper to run on your Hot Tub.

  • Low carbon footprint
  • Save money on energy bills
  • Can be used for both heating and cooling
  • Can work even in lower temperatures
  • High Seasonal Coefficient of Performance (SCOP)
  • Easy installation process
  • Low maintenance
  • Long lifespan
  • No fuel storage needed

What are the disadvantages are Air Source Heat Pumps?

One of the main disadvantages is the initial outlay – they are not cheap pieces of kit. However, factor in the money that they are going to save you and within 18months to 2 years they will have easily paid for themselves.

  • Lower heat supply than propane or natural gas
  • Lower efficiency below 0°C / 32F
  • Electricity is needed to run an ASHP
  • ASHPs can be noisy

Why are not all Air Source Heat Pumps are the same?

Air Source Heat Pump for Hot Tubs

Air Source Heat Pump for Hot Tubs

Loving a car analogy here at, two 6 litre V8 cars parked side by side are not necessarily the same are they? Yes, they are both cars, but you can pretty much bet they have different features, different performance and different price points. The same goes for Air Source Heat Pumps.

Just because you have two ASHPs that are showing the same heating capacity does not mean that they are the same. Let’s take a look why and also what you should be looking for.

For regular DIY Hot Tub builds, which fall under 3000 litres or 650 gallons, you are going to look for an ASHP that is going to output roughly 12kW of heating capacity which is going to be around 40 000 BTU.

Due to the nature of how an ASHP works, they have different efficiencies at different temperatures. Therefore, you need to pay clear attention to their performance in the temperature range of your environment.

For example, many units are not rated for working under zero degrees Celsius or 32 Fahrenheit. If you are planning to use your tub in the winter, then this is not going to work for you.

Also, you will find that at the cheaper end of the ASHP range, they will consume a huge amount of power at lower air temperatures but also have a lower heating output. Basically, they don’t work well in the cold.

The key is to look for the consumed power at a specific outside temperature and you can then look at the heating capacity at this temperature too. If you compare a cheap unit side by side with a more expensive unit, you will see that the power consumption on the more expensive unit is lower and the heating capacity is also greater. This is because the unit is more efficient.

Warranty. Do check the warranty of Air Source Heat Pumps for Hot Tubs. The cheaper units tend to have only a single year warranty which if you are spending over a grand on a piece of kit, seems a little off to me.

What about the running noise. Pay close attention to the decibel output level of the unit. The cheaper models tend to be a little on the noisy side which if you have neighbours close by, could be a problem.

Now it is time for the clever bits. These are the things that really set aside the differences between a cheap ASHP and a good quality one.

Inverter on the Motor

This sounds complicated but let me explain it in its most basic form. If a motor is inverted, this means that it has “technology” that can control how fast or slow it runs. Why is this important? Well, a fully inverted motor can run at anywhere between 1% and 100% of speed.

If you motor is not inverted, it will only have set speeds. Perhaps, slow, medium and fast. This means that a fully inverted motor is much more efficient as the technology can sense that the motor only needs to be running at 21% for example to reach the desired temperature. An un-inverted motor might have to run at medium for this which would be 29% faster using 29% more energy than our inverted motor. Therefore, there is a saving of running costs. An ASHP with a fully inverted motor will save you roughly a third on the running costs!

Soft Start Motors

Cheap Air Source Heat Pumps will not come with a soft start motor? Why is this important? When a traditional motor starts, it needs more power initially to get it to turn. To do this, it draws more current from your circuit for split second. This is known as a spike. A current spike if it is big enough can knock out your breaker killing the power to your whole hot tub system.

Soft start motors avoid this as they are specifically designed to be able to start to turn without the need of drawing excess power from the circuit thus avoiding the spike on your system. A good quality ASHP will have a soft start motor in it.

Heated Lines

Better quality ASHPs come with heater lines often referred to as a heated train. What this does is at lower temperatures, the unit can sense if the refrigerant lines are likely to freeze and it sends a warm flow of fluid down to defrost them. How clever is that.

So there we have it. In conclusion, we’ve learnt what an ASHP is, how it works and the different types of pumps available as well as what features to look for when you are shopping for your own.

Happy Tubbin’

By |2021-03-11T20:10:18+00:00March 11th, 2021|Build A DIY HOT TUB|Comments Off on The Ultimate Guide to Air Source Heat Pumps for Hot Tubs
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