Vaillant aroTHERM Plus vs Mitsubishi Ecodan: The Premium Heat Pump Shootout
If you've done any research on heat pumps in the UK, you've almost certainly come across these two names. Vaillant and Mitsubishi are the top of the market. Both are excellent, both are widely installed, and both are approved for the Boiler Upgrade Scheme grant. So which one should you choose?
The honest answer is: you won't go wrong with either. But they have real differences, and depending on your situation, one is likely the better fit.
Specs at a Glance
| Feature | Vaillant aroTHERM Plus | Mitsubishi Ecodan |
|---|---|---|
| What the maker advertises | COP up to 5.4, with no test condition stated | SCOP 4.49–4.62 on the R290 PUZ-WZ range |
| What you'll actually get | A seasonal COP around 3.5 in a well-installed system | A seasonal COP around 3.3 in a well-installed system |
| Refrigerant | R290 (propane, low GWP) | R32 |
| Noise level | 51–60 dB(A) sound power across the range (44 dB(A) is the advertised 3.5kW figure) | 40–58 dB(A) across the range, model dependent |
| Installed cost | £9,000–£13,000, usually at the top of that range | £9,000–£13,000 |
| Warranty | 2 years standard, up to 7 with a Vaillant cylinder and a Platinum or Renewable Partner installer | 3 years standard, up to 7 through a Business Solutions Partner |
| Installer network | Growing | Very large: well-established |
| Track record in UK | Newer to market | 10+ years of UK installations |
| Future-proofing | Excellent (R290 is future standard) | Good (R32 being phased down longer-term) |
The Case for Vaillant
On paper Vaillant edges ahead. It publishes a COP of up to 5.4 for the R290 aroTHERM plus, though it's worth noticing what's missing: no test condition is stated anywhere alongside it, there's no SCOP published at all, and Vaillant writes the figure as "a COP of up to 5.4 kW", which is a unit error since COP is a ratio. Mitsubishi, by contrast, publishes a proper SCOP of 4.49 to 4.62 for the R290 Ecodan range.
Don't plan on either. A brochure COP is one test point in a laboratory, usually at 7°C outside with a 35°C flow, and the number you live with is the seasonal average across a whole British winter. For both of these that's somewhere around 3.3 to 3.5 in a properly commissioned system. If anyone builds a running-cost estimate on 5.4, they're using a lab result as a bill.
The bigger deal is the refrigerant. Vaillant's aroTHERM Plus uses R290 (propane), which has a global warming potential (GWP) of just 3. Compare that to R32, which has a GWP of 675. The EU and UK are moving towards natural refrigerants like R290. If you want a heat pump that's environmentally ahead of the curve and won't face regulatory complications in the future, Vaillant is the better choice.
The guarantee is another mark in Vaillant's favour, but read the conditions. The standard cover is 2 years. Getting to 7 requires the unit to be installed alongside a Vaillant cylinder by a myREWARDS installer and registered properly. That's a good deal if your quote already includes a Vaillant cylinder and a real problem if it doesn't, so ask the question before you sign rather than after.
The Case for Mitsubishi
Mitsubishi has been installing Ecodan heat pumps in the UK for over a decade. That matters more than it sounds. There are thousands of trained Ecodan installers across the country, which means it's easier to find someone local who really knows the product inside out. That installer familiarity leads to better commissioning, better performance, and fewer problems.
Real-world data on the Ecodan is extensive. It performs well, it's reliable, and when something does go wrong, parts and expertise are readily available. Vaillant's aroTHERM Plus is newer to the UK market. The efficiency numbers are great, but you're relying on a shorter track record.
The Ecodan usually comes in a bit cheaper too. The Energy Saving Trust puts a typical air source install at around £12,000, and in practice Vaillant quotes tend to sit at the top of the £9,000 to £13,000 range while Ecodan quotes sit nearer the middle. That's an observation from quote patterns rather than a published statistic, so get three quotes and check it yourself. Whatever the gap is, it's money you could spend on better radiators or a bigger cylinder instead.
Noise: Does It Matter?
Both make a noise, and both manufacturers advertise the flattering number. Vaillant's headline is 44 dB(A), "our quietest air-to-water heat pump", and the footnote says that's based on the 3.5kW model. Its older page manages "sound power as low as 54 dB(A) in a 3 metre distance", which is self-contradictory, because sound power doesn't have a distance.
Go to the ErP data sheets instead, where the row is unambiguously labelled sound power. Across the aroTHERM plus range that's 51 to 60 dB(A). Mitsubishi publishes 40 to 58 dB(A) across the Ecodan range. So on a like-for-like basis the Ecodan range is, if anything, the quieter one at the top end, which is the opposite of what the marketing implies.
Either way, ask each installer for the sound power level (LwA) of the exact unit they're quoting, and for the completed calculation. Permitted development in England is conditional on meeting the MCS Planning Standards, specifically MCS 020 a, the air source heat pump sound calculation, assessed at your nearest neighbour's habitable-room window. Sound power is what that calculation uses and the only figure comparable across brands. Sound pressure is a different and smaller number, quoted at whatever distance flatters the product, and the gap between the two is easily the difference between a pass and a fail. An installer who can't produce the LwA on request is not the installer you want.
What Should You Actually Do?
Here's the practical advice: find a good installer first, then ask what they recommend. A heat pump is only as good as its installation. A perfectly specified Vaillant installed badly will underperform a well-installed Ecodan every time.
If your installer is highly experienced with Vaillant's aroTHERM Plus and enthusiastic about it, go with Vaillant. The efficiency and refrigerant advantages are real, and a confident installer will get the best out of it.
If your installer is primarily an Ecodan specialist (and many of the best heat pump engineers in the UK are), go with Mitsubishi. The track record is excellent and you'll benefit from their deep knowledge of the product.
If you're choosing between installers, and one quotes Vaillant while another quotes Mitsubishi, don't let the product be the deciding factor. Look at the installer's MCS certification, their reviews, and their commissioning process. That's what will make the difference to how warm your house is and how low your bills are.
The Verdict
Vaillant if you want the most efficient, future-proofed option and you can find a good installer who knows the product. Mitsubishi if you want a safe, proven choice with a massive installer network behind it. Genuinely, you won't regret either one. For detailed reviews, see our Vaillant Arotherm Plus review and Mitsubishi Ecodan review. For the wider picture, see our best heat pumps UK guide and heat pump costs guide.