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.
Flexible Space Function: standard on both now
Both the pro and the current-generation plus now include a feature called Flexible Space Function (FSF), which shrinks the safety exclusion zone required around the outdoor unit. Activate it and the fan runs at a low, continuous speed, even when the heat pump isn't heating. That constant airflow disperses any leaked refrigerant before it can build up, which is the actual risk the exclusion zone rules exist to guard against. Because the risk is managed actively instead of by distance alone, the exclusion zone shrinks from one metre in every direction to just the area directly below the unit. In practice, that means either heat pump can go into corners, tight side returns, and spots close to walls or fences that would rule out a standard R290 installation.
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.
Both heat pumps solve this with Flexible Space Function. Activate it and 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, so the exclusion zone shrinks to just the area directly below the unit. Corners, side returns, and spots close to walls or fences that would rule out a standard R290 heat pump become viable with either one.
That's true for both heat pumps now. Where they still differ is size: the plus grows to a twin-fan casing at 10 kW and 12 kW. Every pro size, including its 11 kW, stays on a single fan.
All three pro sizes, the 5 kW, 7 kW, and 11 kW, use a single fan. The plus moves to a twin-fan casing at 10 kW and 12 kW, which takes up more space. If you're already nervous about the visual impact of an outdoor unit, the pro's single-fan design across its full range is a genuine reassurance. It's a smaller unit, easier to tuck against a wall or into a side return.
If your heat loss calculation puts you around 11–12 kW, you're choosing between the pro's single-fan 11 kW and the plus's twin-fan 12 kW. Two fans need more depth and width than one to move the same air, so the plus's casing grows once you cross into the 10 kW and 12 kW models. The pro's 11 kW keeps the same compact footprint as the 5 kW and 7 kW units. That makes it easier to site against a wall or tuck into a side return, and it stands out less in the garden. Weigh the twin-fan plus against the single-fan pro before you commit to the bigger box.
Noise
This is one of the sections we most needed to revisit. When we first compared these two heat pumps, the plus ran at 51 dB(A) (5 kW) and 53 dB(A) (7 kW), against the pro's 49 dB(A) at both sizes, and the pro came out quieter. Vaillant has since updated the plus. The current generation runs at 44.3 dB(A) and 46.8 dB(A) at those sizes, quieter than the pro at every comparable size.
At the top of the range it's the same story: the plus runs at 50.0 dB(A) at both 10 kW and 12 kW, against the pro's 54.8 dB(A) at 11 kW. For installations near bedroom windows, neighbouring properties, or anywhere noise matters, the plus is now the quieter option across the board.
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 used to ship in white. Vaillant now makes it in anthracite (RAL 7021) as standard, the same finish as the pro. Colour is no longer a reason to choose one over the other. The pro still ships with an optional base skirting that hides the feet for a cleaner finish at ground level; check whether the plus offers the same before deciding it matters.
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, since the majority of properties fall comfortably within the 5 to 11 kW range. But if a proper heat loss assessment puts you below 5 kW or above 11 kW, the plus is your only Vaillant option. Check with your installer, who can 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
Our recommendation has changed since Vaillant updated the plus. The pro still costs less and stays on a single fan right up to 11 kW, which matters if your outdoor space is tight. The plus is now the quieter option at every size, matches the pro's anthracite finish, has the same Flexible Space Function, and carries a longer guarantee through Heat Geek. For most UK homes, either one performs well; the choice comes down to price, guarantee length, the exact size you need, and how tight your outdoor space is.
The plus makes clear sense in a few 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, noise or guarantee length is the deciding factor, 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.
