German Home Renovation with an Air-to-Water Heat Pump
Upgrading an older German house with an air-to-water heat pump involves much more than replacing the existing heating equipment. The building envelope, insulation and heat distribution system all play an important role in the overall performance of the installation. This case study follows a complete renovation project, from structural preparation and insulation improvements through to low-temperature underfloor heating and the installation of an air-to-water heat pump.
Project Overview
- **Location:** Germany
- **Property type:** Existing residential house
- **Project scope:** Interior renovation and full heating-system upgrade
- **New heat source:** Air-to-water heat pump
- **Heat distribution:** Water-based underfloor heating
- **Supporting work:** Ceiling insulation, internal wall lining, floor preparation
- **Outcome:** Whole-house low-temperature heating system replacing the original setup
The Starting Point
The renovation began by exposing the existing ceiling structure, allowing the construction team to inspect the timber framework and prepare the building for the next stages of the project. Opening the ceiling also created space for insulation upgrades and service routing before the internal finishes were rebuilt.
As with many renovation projects, improving the building envelope before installing the heating system helps create a more suitable environment for low-temperature heating. Insulation, floor construction and equipment placement were therefore considered together during the planning stage rather than as separate tasks. For a broader look at retrofitting underfloor heating into an existing property, see our guide: [Can Underfloor Heating Be Installed in an Existing House? A Retrofit Guide](https://www.nordthermglobal.com/blog/can-underfloor-heating-be-installed-in-an-existing-house-a-retrofit-guide).
Why an Air-to-Water Heat Pump with Underfloor Heating
An air-to-water heat pump performs best when paired with a low-temperature heat emitter. Underfloor heating spreads warmth across the entire floor area rather than concentrating it at a single radiator running at a much higher flow temperature. Once insulation had been improved, the heating system could be designed around the thermal performance of the renovated building.
This is also why the insulation and structural work came first. A heat pump installed into a poorly insulated building will run constantly at higher flow temperatures to compensate, which reduces efficiency and shortens equipment life. Treating the building fabric, the underfloor heating and the heat pump as one connected system — rather than three separate jobs — was the central decision behind this renovation.
Construction Process
Opening the Ceiling and Improving Insulation
The original ceiling finishes were removed first, exposing the timber joists for inspection. This also allowed electrical cabling and other services to be rerouted cleanly before the structure was closed again — work that is far easier to complete at this stage than after the insulation and boards are fitted.
Mineral wool insulation was cut and fitted between the joists, with attention paid to avoiding gaps that would otherwise become thermal weak points. Reducing heat loss through the ceiling matters directly to heat pump performance: every degree of heat retained by the building is a degree the heat pump doesn't have to generate.
Once the insulation was in place, the ceiling and walls were boarded to create a finished internal surface ready for the next stage of the renovation.
Preparing the Floors for Underfloor Heating
With the ceiling and wall work complete, attention moved to the floors. The rooms were cleared down to a suitable base, and the layout was checked against door thresholds and adjoining floor levels before the underfloor heating components were brought in.
Insulated floor panels were laid first, providing a defined route for the pipework and directing heat upward into the room rather than down into the subfloor. Edge insulation was fitted around the perimeter walls to allow for thermal movement and reduce heat loss at the edges of each room.
Laying the Underfloor Heating Pipework
The heating pipes were laid in continuous loops and connected back to the manifold. Careful pipe spacing helps promote even floor temperatures and contributes to consistent comfort throughout the heated areas.
Metal heat-spreading plates were fitted over the pipework to distribute heat evenly across the floor surface. The completed layout was checked room by room before the floor build-up was closed over it.
Heat Pump Integration
The outdoor air-to-water heat pump was installed on a solid, level base beside the house, positioned to allow unobstructed airflow through the unit while keeping the pipe run back into the property as direct as possible.
Connected to the renovated underfloor heating system, the heat pump now operates at the lower flow temperatures the building was specifically prepared for. Rather than producing short bursts of high-temperature heat the way a boiler-and-radiator system would, the combination delivers steady, even warmth across each room — drawing on the insulation work completed earlier in the project to keep the heat pump running efficiently rather than compensating for an under-insulated building.
This project used the heat pump for space heating only. Many [air-to-water heat pumps](https://www.nordthermglobal.com/products/r290-air-to-water-split-heat-pump-for-heating-cooling-and-hot-water) can also be configured to provide cooling and domestic hot water from the same outdoor unit — see our guide: [Can One Air-to-Water Heat Pump Provide Heating, Cooling, and Domestic Hot Water?](https://www.nordthermglobal.com/blog/can-one-air-to-water-heat-pump-provide-heating-cooling-and-domestic-hot-water)
Finished Project
Following the completion of the renovation, the house now benefits from a modern low-temperature heating system combining improved insulation, water-based underfloor heating and an air-to-water heat pump. Together, these elements create a system designed for steady indoor comfort and improved energy efficiency.
Project Takeaways
This project highlights the importance of treating a heat-pump renovation as a complete building upgrade rather than simply replacing the heat source.
That sequencing matters specifically when retrofitting a heat pump into an older property. Before any equipment is selected, the building's heat loss, available floor area, required flow temperature and a suitable outdoor unit position all need to be understood. The final heat pump capacity should always be based on a room-by-room heat-loss calculation — not on matching the output of the boiler it's replacing.
Before starting a similar retrofit, the following should be assessed:
- Existing insulation levels in ceilings, walls and floors
- Available floor height for underfloor heating panels and build-up
- Room-by-room heat loss calculation
- Required flow temperature for the selected heat pump
- Outdoor unit position and airflow clearance
- Pipe layout and manifold capacity for the number of heating circuits
Renovation work of this scope also affects overall project cost. For a broader look at what drives heat pump installation pricing, see: [Why Is Air-to-Water Heat Pump Installation So Expensive?](https://www.nordthermglobal.com/blog/why-is-air-to-water-heat-pump-installation-so-expensive)
Frequently Asked Questions
Can an air-to-water heat pump be retrofitted into an older German house?
Yes, when the building fabric is prepared to support lower flow temperatures. This typically means improving insulation in the ceiling, walls and floors before or alongside the heat pump installation, so the system isn't compensating for excessive heat loss.
Does underfloor heating work better with a heat pump than radiators?
Underfloor heating distributes heat across a much larger surface area than a radiator, which allows it to run at lower water temperatures for the same level of comfort. This generally suits the operating range of an air-to-water heat pump more closely than a high-temperature radiator system.
Why was the ceiling opened up before installing underfloor heating?
Opening the ceiling allowed insulation to be improved and electrical services to be rerouted before the floor and heating work began. Completing this structural work first avoids having to disturb the finished underfloor heating or flooring later in the project.
How is heat pump capacity sized for a renovation like this?
Capacity should be based on a room-by-room heat loss calculation that accounts for the building's insulation, window area, floor area and target indoor temperature — not simply matched to the output of the boiler being replaced.
Can this type of retrofit be done in stages?
Yes, though the sequence matters. Insulation and structural work are best completed before the underfloor heating is installed, and the heat pump should be sized and commissioned only once the building's heat loss has been properly assessed.
Planning a Similar Heat Pump Renovation?
Every renovation project is different. Building insulation, room layout, heat loss and heating requirements should all be evaluated before selecting a heat pump system. If you're planning a similar renovation, our team can help you choose an air-to-water heat pump solution suited to your property and project goals.
[View our air-to-water heat pump range](https://www.nordthermglobal.com/products/r290-air-to-water-split-heat-pump-for-heating-cooling-and-hot-water)
