Heat pumps in terraced and semi-detached houses

A terraced house or a semi-detached house is often well suited for a heat pump: the shared walls save heat, and the heating load is manageable. The real challenge lies outside. The garden is narrow, the neighbour's bedroom window is just a few metres away, and the outdoor unit of an air-source heat pump makes noise. Planning carefully here avoids the most common point of contention surrounding heat pumps.

Why noise plays the leading role in terraced houses

According to an information sheet from the Umweltbundesamt (Environment Agency Austria) and the Environment Ministry (Forum Schall, 2013), air-source heat pumps repeatedly lead to complaints, mostly regarding outdoor units. The low-frequency component, the typical 'humming', is perceived as particularly disturbing.

For guidance, the information sheet specifies two target values for the night:

Directly in front of the neighbour's living areas: a maximum of 25 dB. In quiet residential areas, experience shows that the night-time background noise level is between 20 and 25 dB, according to the information sheet.
At the property boundary to residential building land: 30 dB, derived from the planning guide values of ÖNORM S 5021. klimaaktiv also specifies this maximum value of 30 dB(A) at night at the property boundary.

These values are planning targets, not uniform nationwide limit values. The rules differ depending on the federal state: some link a permit or notification requirement to certain noise levels, others refer to the ÖNORM. An overview is provided by laerminfo.at. According to this site, neighbours can take civil action even without a permit requirement if the noise exceeds the local customary level. You can find out what is required in your municipality from the Bauamt (building authority).

How far is far enough?

The information sheet contains a table with recommended minimum distances to the neighbouring residential building, depending on the sound power level of the appliance and the installation location. A few values from this, in each case without additional noise protection measures and for the target value of 25 dB in front of the window:

Appliance with 50 dB sound power: approx. 7 m free-standing, 10 m in front of a house wall, 14 m in a corner.
Appliance with 55 dB: approx. 13 m, 18 m or 24 m respectively.
Appliance with 60 dB: approx. 22 m, 28 m or 35 m respectively.

Two things stand out. Firstly, even a few decibels more on the appliance multiply the required distance. Secondly, a corner or niche, which is often the obvious location in a terraced house, is acoustically the worst choice because the walls reflect the sound.

In a narrow terraced house garden, such distances are rarely achievable. This makes the adjustment options mentioned in the information sheet all the more important:

Choose a quiet appliance. The supplier must state the sound power level. According to the information sheet, state-of-the-art appliances achieve around 56 dB.
Use the side facing away from the neighbour. According to the information sheet, this can bring a reduction of 5 to 20 dB. Reflections from other structural components must be avoided.
Reduce night-time operation. Reducing the speed at night is possible, may require a suitably sized buffer cylinder and must be checked by a specialist.
Enclosure only as a system. Experience shows that acoustic hoods only work as a system solution from the respective manufacturer, with a specifically stated sound power level, according to the information sheet.

With our noise calculator, you can roughly estimate what level will reach your neighbour for your installation location.

Where the outdoor unit can go

Typical locations in a terraced house and their questions:

Front garden facing the street. Often further away from bedrooms, but visible. Ask your municipality whether there are any requirements regarding clearances or the local townscape.
Garden behind the house. Usually closer to the neighbours' terrace and bedroom. Every metre counts here.
Flat roof or garage roof. According to the information sheet, installation on the roof usually has the same effect as a free-standing installation. Structural analysis, access for maintenance and structure-borne noise into the house must be clarified.
Indoor installation. There are appliances that stand in the cellar or plant room and draw in air via ducts. In this case, the air outlet and duct routing come into focus.

With semi-detached houses, there is an additional special feature: if your appliance is located on the boundary to the other half, the sound hits the neighbouring house directly. An open conversation with the neighbours before planning saves a lot of trouble later on.

Split or monobloc

There are two designs of air-source heat pumps:

Monobloc: The entire refrigerant circuit is located in the outdoor unit. Water pipes lead into the house. The appliance should therefore not be too far from the house, and the pipes must be protected against frost.
Split: The outdoor and indoor units are connected via refrigerant lines. This often gives more flexibility for the installation location, but work on the refrigerant circuit requires appropriately qualified specialists.

The design alone is not decisive for the noise issue. The specified sound power level of the specific outdoor unit is what counts.

Pay attention to a deadline regarding refrigerants: according to the info sheet for the 2026 Kesseltausch relaunch, monoblock heat pumps up to 50 kW and split air heat pumps up to 12 kW using a refrigerant with a GWP value above 150 under the EU F-gas Regulation may only be placed on the market until 1 January 2027 at the latest. Air-to-water units with a GWP between 150 and 750 also receive 20 per cent less public subsidy, while above GWP 750 there is none. Therefore, ask which refrigerant the offered unit uses. You can find details on public subsidy conditions in the Förder-Manager.

Checklist before ordering

What is the sound power level of the offered outdoor unit, according to the data sheet?
Where exactly should it stand, and how far is the nearest window of a living area at the neighbour's house?
Is the appliance standing in a corner, niche or in front of a reflective wall?
Is there a night or whisper mode, and how does it affect performance?
What requirements does my municipality or federal state have? Is a notification or permit required?
Have I spoken to the neighbours?
Which refrigerant does the appliance use?

If the garden is too small for an air-source heat pump, a ground-source heat pump can be an alternative. The differences are explained in the guide Air or ground source. For permits in general, see Permits.

Your next step

In a terraced house, it is worth discussing the installation location during the very first on-site appointment. Via our request for quotes, you will receive quotes from a maximum of three checked installers. Please ask each installer to write the sound power level and planned installation location in writing in the quote: this way you can compare the quotes directly.