There is certainly a lot of confusion around Air Source Heat Pumps and which model we should select for our Hot Tubs and Pools. Everyone under the sun seems to be selling a model now and more and more brands are popping up every day. I’ll be honest, I’ve never heard of most of the ones I get asked about!
I’ve tried on my website to keep the range that I offer for sale to a minimum. Minimum being that I offer a model or range to suite everyone and everyone’s budget or requirements.
Lack of Manufacturer Specifications and Exact Statistics
One of the things that is really evident across this industry, right since I stumbled upon air source heat pumps, is that there is a lack of statistics. One of the things that I have tried to do as I help more of you with your conversions over to Air Source is get some real-world statistics that don’t come from a lab. I have lots of articles on this blog and my YouTube Channel about the numbers and what my customers and I have found.
I’ll try and stay away from the “lab numbers” in my articles and analysis and hopefully share some real word data and insight to help you making the right decision about your purchase. Also, it is not aways a good way of comparing models unless you fully understand what the manufacturer statistics actually mean – remember – they are there to help sell the unit to you the consumer!
All Season Versus 2-3 Seasons
The first thing that I would say is that the main difference between the Onda range of Air Source heat Pumps and the Comfortline is the “working period”. What I mean by this is the ambient temperature in which the units will work.
The Comfortline is rated to zero which means that the manufacturer is comfortable saying that you are going to get heat out of the unit when the ambient temperature is zero. Having run my own at sub zero temperatures, I know this to be the case. Therefore, you can class the Comfortline as an All Season heat pump.
The Onda by contrast is only rated to 10C which means that the manufacturer will not guarantee heat at temperatures below this. For us in the UK, this means that this really is only a spring and a summer, plus some of autumn, at best a two to three season heat pump. Our winter and late autumn are generally colder than this which means it may not heat and there is a chance it will freeze up.
If you are only looking to use your tub or pool during the warmer months, then the Onda is still a great choice, especially given its lower price point.
COPs are Similar on both ranges
One of the reasons that I offer both the Onda and the Comfortline is that the COPs or the Coefficient of Performance is around 6 for each model. What this means is that for every KW of electricity you put into the unit, you can get a maximum (in perfect air temperatures) of 6KW out.
I should point out here that the COPs do decrease as the ambient temperature decreases and also if the humidity changes too – these are the two factors that have the biggest impact on the COP. This is of course the same for any air source heat pump.
Plug in versus Hard Wired
You may have noticed that on the Onda range, they are a plug in unit that plugs straight into a socket in a 13A supply. The Comfortline are hard wired which means you may need to get an electrician to do this for you if you are not a competent DIYer.
This doesn’t really change the performance, but you can see with a plug in unit it is not designed to be permanently installed and you will pack it away for the winter months for example.
The connection pipework for the Onda and the Comfortline are different too. The Onda, once again is going down the route of offering pipework that is easily removed so that you can pack the unit away and store it over winter. Using 38mm flexible pipe and jubilee clips to make the connections, it is not a permanent install.
The Comfortline on the other hand is designed to be solvent welded into place. All of the joints are designed to be permanent and you will be most likely using 1.5” rigid pipe and PVC solvent weld joints.
The main point here is the Onda is not designed to be a permanent install whereas the Comfortline is.
In conclusion, both the Comfortline and the Onda will be able to offer you considerable savings over running your hot tub or pool on electric. Both have a good COP, but as we have seen, this will depend on the time of year and the ambient temperate to determine the exact heating benefit you will see.
The Onda clearly is designed to be a temporary solution, not a permanent install. I think I would liken the Onda to the word of Air Source Heat Pumps just as the inflatable hot tub is to the world of hot tubs. A cheaper price point to entry to “test the water” as so to speak to see if air source is in fact the way forward for you. But is not something you would be leaving out all rear round.
That said, if you only use your tub during the warmer months of the year, then given the cost of the Onda, this is a great route to take.
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Thanks - Andi
Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.
Today, I've helped over 1000 DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi