Vaillant aroTHERM pro vs plus: Which Heat Pump is right for you?
For many homes, the aroTHERM pro heat pump is newer, cheaper, quieter and more versatile on space than the aroTHERM plus. However, the plus offers more size options, which matters for some older homes or homes with a very small heat loss.
If you're looking at Vaillant heat pumps you'll probably come across both the aroTHERM pro and the aroTHERM plus. They use the same refrigerant, come from the same manufacturer and do the same basic job. The choice between them isn't always obvious, so let's go through what's actually different and what the specs mean in practice.
What's new
You've likely heard about a new flagship feature - the Flexible Space Function (FSF). FSF is a feature built into the aroTHERM pro that reduces the safety exclusion zone required around the outdoor unit. When FSF is activated, the unit's fan runs at a low, continuous speed even when the heat pump isn't actively heating. That constant airflow prevents any leaked refrigerant from building up around the unit, which is what the exclusion zone rules are designed to guard against. Because the risk is managed actively rather than just by keeping the area clear, the exclusion zone can shrink from one metre in all directions to just the area directly below the unit. In practical terms, it means the pro can be installed in corners, tight side returns and spots close to walls or fences where a standard R290 heat pump couldn't go.
The comparison at a glance
What they share
Both are R290 heat pumps made by Vaillant. Both use the sensoCOMFORT controller. Both support wall mounting. Both have a noise reduction mode. Both are backed by Vaillant's UK warranty and service network and are eligible for the Boiler Upgrade Scheme grant.
The core engineering platform is the same. If your instinct is that the pro being cheaper must mean it's worse, that's not what's happening here. They're different products suited to slightly different situations, not a premium and a budget version of the same thing.
Where the aroTHERM pro has the edge
Space: this is the big one
R290 is propane. It's a natural refrigerant, but it's flammable, which means R290 heat pumps have to meet strict rules about where they can be sited. Specifically, there has to be a clear exclusion zone around the outdoor unit free from potential ignition sources: no plug sockets, no light switches, no openable windows or doors within a set distance.
On a standard installation, that zone extends one metre from the unit in every direction. In a typical UK garden with fences, gates, back doors, and sockets close together, finding a spot that clears a one-metre exclusion zone on all sides takes some work. On a compact urban plot it can genuinely run out of options.
The aroTHERM pro has a Flexible Space Function that solves this. When activated, the unit's fan runs continuously at a low speed, even in standby. That constant airflow disperses any potential refrigerant leak before it can build up, which means the exclusion zone shrinks to just the area directly below the unit. Corners, side returns, spots close to walls or fences that would be ruled out with the plus become viable with the pro.
The plus has no equivalent. If your outdoor space is constrained, this difference can determine which unit is actually installable.
The aroTHERM pro also has a smaller physical footprint than the plus. All three sizes, the 5 kW, 7 kW, and 11 kW, use a single fan. The aroTHERM plus moves to a twin-fan unit at 10 and 12 kW, which means a significantly larger casing. For homeowners who are already nervous about the visual impact of an outdoor unit, the pro's single-fan design across the full size range is a genuine reassurance. It's a more compact unit that takes up less space and is easier to tuck away neatly.
Noise
This one surprised us when we looked at the specs carefully. The aroTHERM plus has a strong reputation as a quiet unit, and it is. But the pro is a little quieter.
At 5 kW, the plus measures 51 dB(A) sound power against the pro's 49 dB(A). At 7 kW, the plus is 53 dB(A) against the pro's 49 dB(A). That four-decibel gap at the 7 kW is potentially meaningful. For installations near bedroom windows, neighbouring properties, or anywhere noise matters, the pro is the better choice. The plus's reputation for quiet operation is deserved, but it's the older unit and the pro improves on it.
Price
The pro costs less than the plus. The difference will vary depending on timing and merchant, but the pro seems to be coming in slightly cheaper than the plus. For most homes there's no performance reason to spend the extra on the plus.
How it looks
The plus is white. The pro is anthracite. For lots of people, this might not matter! But for some, a white heat pump may stand out in a way that not everyone loves, especially if you have a modern home with grey render, dark window frames, or composite doors. The anthracite finish sits more naturally against contemporary exteriors. The optional base skirting on the pro, which hides the feet for a cleaner finish at ground level, adds to that. Neither is a reason on its own to pick one over the other, but the pro is a genuine improvement aesthetically.
Where the aroTHERM plus has the edge
Size range
The plus comes in 3.5 kW, 5 kW, 7 kW, 10 kW, and 12 kW. The pro comes in 5 kW, 7 kW, and 11 kW. For most UK homes this doesn't matter. The majority of properties in the UK fall comfortably within the 5 to 11 kW range. But if you have a small flat or compact property where a 3.5 kW is the right size after a proper heat loss assessment, or a larger home that needs 12 kW, the plus is your only Vaillant option. As always - check with your installer who will be able to advise properly based on your own home.
Track record
The plus has been installed across the UK for several years. There's real-world performance data, published case studies, and a wide base of Heat Geek installers who have worked through its edge cases and know it well. The pro is new to market. It will build that history, but right now the plus has the longer track record. For homeowners who want to buy a well-proven product that's been tested in a wide range of UK conditions, that could be a legitimate consideration. But, with Vaillant as the manufacturer, we don't anticipate any problems.
Our view
For most UK homes, we'd recommend the aroTHERM pro. It's quieter than the plus, fits more spaces, costs less, and looks better on modern properties. Those are genuine advantages, not marginal ones, and for a typical UK home none of the plus's advantages are likely to apply.
The plus makes clear sense in three situations: you need a size outside the pro's 5 to 11 kW range, your property genuinely requires high flow temperatures and the radiators can't be upsized, or you have a strong preference for a product with a longer UK installation history.
If you're not certain which applies to your home, that's what a Heat Geek Design Consultation is for. We'll do a proper heat loss assessment, look at your outdoor space, and give you a straight recommendation.
