Siting an aroTHERM plus: protective zone and the sound figures
R290 puts a dimensioned exclusion zone around the outdoor unit, and Vaillant's sound power rises with flow temperature. Both decide where the unit can stand.
What this means
R290 is heavier than air, so Vaillant defines a protective zone around the outdoor unit. Nothing inside it may be a window, door, light shaft, cellar entrance, escape hatch, flat-roof window, ventilation opening, or permanent ignition source, and the zone may not reach an adjacent building or a public traffic area. For ground installation on the premises the operating instructions give that zone as 1000 millimetres.
Equipment and model context
Vaillant aroTHERM plus, VWL 35/6 to VWL 125/6
- VWL 35/6 at 3.5 kilowatts
- VWL 55/6 at 5 kilowatts
- VWL 75/6 at 7 kilowatts
- VWL 105/6 at 10 kilowatts
- VWL 125/6 at 12 kilowatts
Figures taken from the Vaillant operating instructions covering VWL 35/6 A 230V S2 to VWL 75/6 A S2, document 0020330791_01. Zone dimensions differ by installation type, the manual gives several, and the installation manual for the model actually supplied is what governs a real position.
What this guide covers
- A proposed outdoor unit position sits under a window or beside a cellar light well.
- A boundary or a neighbour's wall is close to the only sensible position.
- A survey moved the unit and the reason given was the refrigerant rather than the pipework.
What changes the answer
- R290 is denser than air, so a leak collects at low level and near openings.
- Sound power is published per operating condition and rises with the water temperature.
What the protective zone excludes
Vaillant's reasoning is stated plainly in the operating instructions: R290 has a higher density than air, so escaping refrigerant may collect near the ground, and it must not reach the inside of a building through an opening or settle in a groove.
The list of things that may not sit inside the zone is specific. No windows, doors, light shafts, cellar entrances, escape hatches, flat-roof windows, or ventilation openings. No permanent ignition sources, and the manual names plug sockets, light switches, lamps, and electrical switches as examples. The zone may not extend to an adjacent building or to a public traffic area.
There is a clause that reaches beyond the installation day as well: no later structural alteration may be made that breaks those rules. A window added afterwards into a wall that the zone touches is a change to the installation, not a change to the house.
The dimensions change with how the unit is mounted
The manual does not give one number. Ground installation on the premises is dimensioned at 1000 millimetres. Ground installation in a building corner is drawn with several dimensions at once, running from 200 or 250 millimetres up to 2600 and 3100. Flat-roof installation is given as 1000 millimetres.
The pattern behind that is enclosure. A unit standing in open ground disperses a leak in every direction, and a unit tucked into a corner has two walls holding it, so the zone has to reach further along the ground before the concentration falls.
This is why moving a proposed position by half a metre can change what the installer is willing to sign off. The distance to the wall changes which drawing in the manual applies, and the drawings are not interpolations of one another.
Sound is published at three conditions, not one
The specification table gives sound power under EN 12102 and EN 14511 at A7/W35, A7/W45, and A7/W55. On the 3.5 and 5 kilowatt units the readings are 51, 53, and 54 dB(A), so the quiet figure quoted in brochures is the low-temperature one.
Three decibels is a doubling of acoustic power. A system designed to run at a 55 degree flow temperature is at the top of that range through the heating season rather than the bottom, which matters where the position is close to a boundary.
The 7 kilowatt unit reads 53, 53, and 55, so it matches the smaller pair at the middle condition and sits above them at either end. A single quoted number would not predict that.
The step between 7 and 10 kilowatts
The cabinet grows from 965 millimetres tall on the VWL 75/6 to 1565 on the VWL 105/6, and the sound power goes from 53 to 58 dB(A) at A7/W35. Five decibels arrive in one step of the range.
Above that the range flattens. The 10 and 12 kilowatt units share the cabinet height and publish identical figures of 58, 58, and 60. Sizing up from 10 to 12 costs nothing acoustically; sizing down from 10 to 7 recovers the five decibels.
Vaillant lists Quiet Mark accreditation for the 3.5, 5, 7, and 12 kilowatt outputs and does not list the 10, despite the 10 and 12 publishing the same figures. That is worth checking against current Vaillant literature for a specific project rather than reading either way.
What R290 removes and what it does not
Vaillant states that R290 is exempt from the European F-gas regulation, which removes the periodic leak-checking and record-keeping duties that attach to a fluorinated refrigerant above a threshold charge.
It buys the flow temperature as well. The range reaches 75 degrees Celsius and operates down to minus 25 outdoors, and Vaillant states it can use existing radiators, which is what keeps an emitter replacement programme off the critical path in a retrofit.
What it adds is the zone. The exemption from one regulation and the arrival of a dimensioned exclusion around the unit are the same property of the fluid seen from two sides.
| Feature near the position | Why it matters |
|---|---|
| An opening window or a door | Named as excluded from the protective zone |
| A cellar entrance or light shaft | Named, because R290 collects at low level |
| An external socket or light switch | A permanent ignition source inside the zone |
| A neighbour's wall or a pavement | The zone may not extend to either |
| A building corner rather than open ground | A different drawing with larger dimensions applies |
| A gully or downpipe | Vaillant states these pose no risk inside the zone |
| Model | A7/W35 | A7/W45 | A7/W55 |
|---|---|---|---|
| VWL 35/6, 3.5 kW | 51 | 53 | 54 |
| VWL 55/6, 5 kW | 51 | 53 | 54 |
| VWL 75/6, 7 kW | 53 | 53 | 55 |
| VWL 105/6, 10 kW | 58 | 58 | 60 |
| VWL 125/6, 12 kW | 58 | 58 | 60 |
Two come from the refrigerant and two from the acoustics. A position that satisfies one pair and fails the other is not a position, which is why siting is settled before the model is fixed rather than after.
- Zone dimensionSet by the installation type, from the manual's drawings
- Openings and ignition sourcesNone permitted anywhere inside the zone
- Sound at the design conditionRead at A7/W55 if the system runs at 55
- Condensate routeDischarged frost-free, gullies permitted in the zone
Questions people ask about this
How far does the aroTHERM plus protective zone extend?
It depends on the installation type. Vaillant's operating instructions give 1000 millimetres for ground installation on the premises and for flat-roof installation, and a set of larger dimensions running to 2600 and 3100 millimetres for installation in a building corner.
Can an aroTHERM plus be installed under a window?
Not where the window falls inside the protective zone. Vaillant's instructions state that the zone must contain no windows, doors, light shafts, cellar entrances, escape hatches, flat-roof windows, or ventilation openings, because R290 is denser than air and can enter a building through them.
How loud is the Vaillant aroTHERM plus?
Sound power runs from 51 dB(A) on the 3.5 and 5 kilowatt units at A7/W35 to 60 dB(A) on the 10 and 12 kilowatt units at A7/W55. The size and the design flow temperature decide which figure applies.
Does an R290 heat pump need F-gas leak checks?
Vaillant states that R290 is exempt from the European F-gas regulation, so the periodic leak-check and record-keeping duties do not attach. The installation requirements that come with a hydrocarbon refrigerant, including the protective zone, still do.
Which aroTHERM plus sizes carry the Quiet Mark?
Vaillant lists the accreditation against the 3.5, 5, 7 and 12 kilowatt outputs. The 10 kilowatt is not in that list even though it publishes the same sound figures as the 12 kilowatt unit.
Can a drain or gully sit inside the protective zone?
Vaillant states that open gullies or downpipes within the protective zone pose no safety risk, and describes routing condensate to a sewer, pump sump, or soakaway. The requirement it does attach is that the discharge is frost-free.
Evidence recordHow this page was checked
official manufacturer support article, operation manual · checked 2026-09-07
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Vaillant technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- official manufacturer support article, operation manual
- Scope of the definition
- Vaillant aroTHERM plus, VWL 35/6 to VWL 125/6
- Last checked
- 2026-09-07