To answer the question you’re here for, Yes, you can add an Air Source heat pump to your existing hot tub. However, there are a few things that you need to consider. In this article, I will explain the steps you have to take and explain how to add an air source heat pump to your existing hot tub.
In this article, I’ll walk you through the entire process, from planning and installation to plumbing and electrical considerations. If you’re looking for a sustainable and cost-effective way to heat your hot tub, this guide is for you!
Many of the larger companies have installation teams that will come out and fit an Air Source Heat pump to your hot tub. However, at buildahottub.com I like to focus on the DIY elements so this article will explain exactly what you need to do.
How big of an Air Source Heat Pump do I need?
The first thing that you need to do is to figure out how big of an air source heat pump you’re going to need. When it comes to choosing the right size Air Source Heat Pump (ASHP) for your hot tub, there’s no one-size-fits-all answer. So to keep it simple—go for the largest unit that fits your budget.
In my opinion, there is no point in adding a 5KW ASHP to your existing Hot Tub. Whilst some may disagree, I don’t believe that the gains are worth the expense. As a bare minimum, again, in my opinion, you should be looking at a 9KW or above for a 4-6 person tub. Any tub larger that this, you should be looking for 12KW as a minimum.
Now, how big is too big? While ASHPs can get pretty large, I’d say there’s no real need to go beyond 24kW for a hot tub. A bigger pump means faster heating, and more importantly, it helps maintain performance when temperatures drop—something a smaller unit (like 5kW) struggles with when its output dips to 2-3kW in colder weather.
This article won’t dive into the benefits of ASHPs—that’s a topic for another time. Instead, I’ll focus on how to properly connect your new heat pump to your existing hot tub setup.
Supplies Needed to Connect an Air Source Heat Pump
Before starting, here are all the supplies that you’d need to connect an ASHP to your hot tub.
- 2” Pipe (various lengths)
- 1.5” or 50mm pipe (short length, depending on union size)
- Pipe Cement
- 90° Elbows (2”)
- 2” Straight Couplers
- 3× Ball Valves
- 2” to 1.5” or 50mm Reducers (check ASHP union size)
Select your Location for your Air Source Heat Pump
The first step in setting up your Air Source Heat Pump (ASHP) is finding the right spot for it. Location is key! You’ll want a place with plenty of airflow, with at least 30cm (12 inches) of clearance from any walls.
You need to make sure that there is nothing in front of the fan. For example, you can’t have the Air Source Heat Pump boxed in or inside of a shed. They don’t work like that. You should always check the manufacturer’s installation guidelines but as a general rule, you must have good air flow right around the unit and they must not be covered or restricted in any way.
How Much Pipe Do You Need?
Next, you need to measure how much pipe you are going to need to get to and from your hot tub. Remember, the water needs to flow into the air source heat pump, be heated, then flow back into the hot tub. Measure the distance to and from the hot tub to your proposed location for your Air Source heat pump, then add 30% extra. This is how much pipe you need.
If your pipes are above ground, insulating them is a smart move. This helps minimize heat loss, keeping your system as efficient as possible.
What size pipe do I need?
Most hot tubs use 2-inch water lines, and I’d recommend sticking with 2-inch piping for your ASHP as well. This ensures proper water flow and prevents any bottlenecks in the system.
How do I connect the Air Source Heat Pump to my hot tub?
Step 1 : Investigate the Existing Setup
This is where the investigation begins. Firstly, you have to identify if you have more than one pump in your hot tub. If you use more than one button to operate the jets then you probably do. If you open the service cover, you should be able to see exactly what you have.
If you have more than one pump, then the chances are you have a circulation pump as well as a jet pump or at least a pump that does the circulation too.
In general, a circulation pump will be the smaller of the two. You may have more than one pump as some larger hot tubs have three or even four pumps.
What you need to do is identify which is the circulation pump or if it is a dual speed pump, which pump is doing the water circulation.
This should be a case of turning on your hot tub and turning up the heat. There will only be one pump running at this point and this is the one that we will need to use to get water to your air source heat pump.
Drain the tub
Now that we have identified which pump is used by the hot tub to heat the water, we now need to drain the tub.
Once we have emptied the hot tub, we are going to need to cut into the water lines of the hot tub so we can attach the Air Source Heat Pump.
As a general rule, you should be looking to cut into the water pipe just after your spa pack. If you are not sure what the spa pack is, this is the square box that has all the pumps, blowers and lights connected to it.
Here is an example of a Spa Pack.
Trace your plumbing
If you trace the plumbing, you should see that water from the lower drains comes into the front of the pump. Then, from the pump it will go into a filter, from the filter into your spa pack and then from your spa pack, it will go back into the jets in the tub.
If you have multiple pumps on your Hot Tub, one of them will follow this plumbing layout and that is the one we want to use.
What we are going to do is cut into the water lines after the spa pack to add the additional heat source which in our case is going to be the air source heat pump.
You will need to remove a 10cm/4” section of the pipe. You can use pipe cutters or a hand saw to do this. Be careful you do not catch any of the other pipework and put holes in anything! Last thing we want is leaks.
With a section of pipe removed, you now need to glue in with PVC Pipe Cement a couple of 90 degree 2” bends to be able to take your pipework outside of the tub over to your air source heat pump.
The chances are that you are going to need to cut holes in the exterior of the tub to allow the new pipework into the system so be mindful of this too.
Manual Bypass on the Air Source Heat Pump
Next you will need to add a manual bypass as shown in the picture above. A manual bypass with ball valves is essential for two reasons:
- Isolation – Allows you to disconnect the ASHP for maintenance or winterizing
- Flow Control – The central gate valve helps manage pressure by diverting excess water past the ASHP if needed.
Note: Opening the bypass reduces heating efficiency since not all water passes through the heating element.
Reduce Down your 2” Pipe to fit the Air Source Heat Pump Unions
In order to minimise the risk of flow reduction, I would be running the pipes to and from the hot tub on 2″ piping. I would be doing this even if the Air Source Heat Pump itself has a different connection. Usually, they are either 1.5″ unions or 50mm connections.
Therefore, I would be converting this over to 2″ so as to increase the flow rates as much as possible in the pipe work.
To do this, you will need some 2″ reducing bushes and then some 1.5″ pipe (or 50mm) to make the connections.
Potential Flow Problems on Single Pump Systems
You have to be mindful that you are adding additional lenghs of pipe as well as bend and junctions within the Air Source Heat Pump. This all adds additional friction for the flow of your water and you may find it affects your jets.
For this reason, we have added into the system a manual bypass valve on your Air Source Heat Pump.
If your flow has been impacted, you can open the manual bypass a little to let more water though. Remember, in doing this is will be less efficient in terms of heating as not as much water will pass into the Air Source Heat Pump.
In the worst case scenario, if your flow is severely impacted, you may need to stop the flow of water all together into the air source heat pump before you use the tub. This would involve closing the inward and outward gate valves and just having the water on the manual bypass.
As I said, this is a worst case scenario and will not be needed in most instances.
Can you Automate the Valves?
If you are into DIY builds and have prior experience, then yes, it is possible to automate the valves. What you can do is use some normally closed 230V solenoid valves. Below shows a smaller 1″ valve, I would not recommend you deviate from the 2″ as the flow will be reduced dramatically.
If you have a dual speed pump, you can wire them off the pump’s low speed connectors. What this means is that when the pump was on low speed, they would be open. They would allow the flow of water through the air source heat pump to be heater.
When you switched to high speed, power would drop and they they would close and divert the water so it didn’t go through the ASHP thus improving the flow to the jets.
The principal here is quite simple. However, this should only be undertaken by a competent DIYer that is more than comfortable with working on electrics as you will be working on 220-240V. You have been warned!
In a Nutshell
Adding an Air Source Heat Pump to your hot tub is absolutely possible and can be a great way to improve energy efficiency while keeping your water warm throughout the year.
If you have any questions or need any help with you connecting an air source heat pump with a DIY hot tub then feel free to reach out to me and I’d love to help!
Can I help you with your Air Source Heat Pump hot tub conversion?
If you need some help with your project, then please get in touch below. I can supply a range of Air Source Heat Pumps, all the supplier you need as well as provide help and guidance on how to fit them.
Happy Hot Tubbin’