R290 Heat Pump for Boiler Replacement

An R290 heat pump for boiler replacement can provide space heating and domestic hot water while allowing a suitable existing radiator, underfloor-heating or fan-coil system to remain in use. However, replacing a gas, oil or LPG boiler is not simply a matter of choosing a heat pump with the same rated kilowatt output.

The installer must first assess the building heat loss, outdoor design temperature, existing emitters, required flow-water temperature, pipework, available electrical supply and domestic hot-water demand.

EXINDA supplies R290 monoblock air-to-water heat pumps for European residential and selected light-commercial retrofit projects. We support distributors, regional partners and qualified installers with model selection, technical documents, hydraulic information, commissioning guidance and spare-parts planning.

Can an R290 Heat Pump Replace a Gas or Oil Boiler?

Yes. An R290 air-to-water heat pump can replace a gas, oil or LPG boiler when the building and heating system are suitable for heat-pump operation.

The strongest candidates usually have:

A reliable room-by-room or whole-building heat-loss calculation
Radiators or other emitters that can meet the load at a practical water temperature
Adequate water flow through the heating system
Space for the outdoor monoblock unit and any required indoor hydraulic components
A suitable electrical supply
A workable domestic hot-water arrangement
Acceptable outdoor-unit position, sound conditions and defrost-water drainage

Existing hydronic distribution can often be retained, but every component should be checked rather than assumed to be compatible.

EXINDA has supplied R290 systems for European retrofit applications, including a UK boiler-to-R290 heat pump project integrating radiator heating and domestic hot water.

Why Boiler Capacity Should Not Determine Heat Pump Size

An existing boiler is often larger than the building’s actual design heat loss. Selecting a heat pump solely from the boiler nameplate can therefore result in unnecessary oversizing.

Oversizing may lead to:

Short cycling during mild weather
Lower seasonal efficiency
Reduced comfort control
Higher equipment and electrical costs
More demanding hydraulic design
Increased outdoor sound at unnecessary output levels

Undersizing can leave the building dependent on supplementary heating during cold weather.

The correct starting point is the calculated building heat loss at the local outdoor design temperature. The selected heat pump must then be checked at the required leaving-water temperature—not only at a mild-weather rating such as A7/W35.

What Must Be Checked Before Replacing a Boiler?

Retrofit item	What the installer should verify	Why it matters
Building heat loss	Design load at the local outdoor design temperature	Establishes the required heating output
Existing boiler	Fuel, output, age and actual operating pattern	Provides context but should not dictate heat-pump size
Heat emitters	Radiator, underfloor or fan-coil output at proposed temperatures	Confirms whether rooms will remain warm
Flow and return temperatures	Actual requirement on the coldest design day	Strongly affects heat-pump capacity and COP
Low-temperature performance	Published capacity at relevant ambient and water conditions	Prevents selection based only on nominal output
Hydraulics	Pipe sizes, pumps, valves, flow rate and pressure drop	Ensures stable circulation and defrost operation
System water volume	Available volume under all zone conditions	Helps prevent cycling and flow faults
Domestic hot water	Cylinder type, storage volume and recovery requirement	Determines DHW system design and control
Electrical supply	Voltage, phase, protective devices and available capacity	Confirms installation feasibility
Outdoor location	Clearances, sound, airflow, snow and drainage	Supports safe, reliable operation
Controls	Heating curve, zones, thermostats and backup logic	Affects comfort and seasonal efficiency

Can Existing Radiators Be Retained?

Existing radiators can be retained if they provide enough heat at the proposed flow and return temperatures.

A boiler may have operated at 70–80°C flow temperature, while a heat pump normally achieves better efficiency at lower water temperatures. The important question is therefore not simply whether the property has radiators, but how much heat those radiators can deliver at the new operating condition.

The installer should:

Calculate each room’s design heat loss.
Identify the installed radiator type and dimensions.
Determine radiator output at the proposed mean water temperature.
Compare available output with the room load.
Increase selected radiator sizes where the output is insufficient.
Balance the system after any emitter changes.

Some properties may need only a few critical radiators enlarged. Others may require broader emitter upgrades or building-envelope improvements before full boiler replacement becomes practical.

The EXINDA R290 installation in a German villa provides a related example of a retrofit using a radiator-based hydronic system.

How Does Water Temperature Affect Performance?

Required water temperature is one of the most important variables in a boiler-replacement project.

As leaving-water temperature rises:

Compressor lift generally increases
Heating efficiency generally decreases
Available capacity may change
Electrical input may rise
Domestic hot-water recovery strategy becomes more important

High-temperature capability can make a heat pump suitable for more retrofit projects, but the maximum published leaving-water temperature should not be treated as the preferred continuous design temperature.

The system should be designed to use the lowest water temperature that can still satisfy the building load. Weather-compensated control can reduce the target water temperature during milder weather and raise it only when outdoor conditions require more output.

Should the Heat Pump Cover 100% of the Design Load?

Not every retrofit requires the same sizing strategy.

Full Boiler Replacement

The heat pump and any integrated supplementary electric heater are designed to cover the project load under the selected design conditions. This approach can remove on-site fossil-fuel combustion, subject to the building, electrical supply and local requirements.

Bivalent or Hybrid Retrofit

The heat pump handles most annual heating demand, while the existing boiler or another heat source operates under defined peak-load or economic conditions.

This may be considered when:

The building has very high peak heat loss
Existing emitters require unusually high water temperatures
Electrical capacity is limited
The owner wants staged renovation
Local electricity and fuel prices support hybrid operation
Resilience or redundancy is required

A hybrid system needs a clear hydraulic and control strategy. Two heat sources should not be connected without defining operating priority, changeover conditions, temperature control and safety logic.

Is a Buffer Tank Always Required?

No. A buffer tank is not automatically required in every R290 heat pump boiler-replacement project.

It may be useful when the system has:

Multiple small zones
Frequent zone-valve closure
Low active water volume
A risk of falling below minimum flow
Short compressor cycles
A need for hydraulic separation
Limited system energy available during defrost
Two heat sources requiring hydraulic decoupling

However, unnecessary buffer volume can increase heat loss, occupy space and complicate the system. The decision should be based on the selected heat pump’s minimum flow and water-volume requirements, the emitter circuit, zoning strategy and system controls.

How Should Domestic Hot Water Be Integrated?

A boiler replacement often includes domestic hot-water production, but the existing cylinder may not be suitable for a heat pump.

The installer should confirm:

Required storage volume
Number of occupants and usage pattern
Cylinder coil surface area
Heat-exchanger capacity at heat-pump water temperatures
Target storage temperature
Recovery time
Legionella-control strategy according to local requirements
Position of temperature sensors
Three-way valve and DHW-priority logic
Need for supplementary electric heating

A heat-pump-compatible cylinder typically needs a heat exchanger designed for the available water temperature and capacity. Reusing an unsuitable cylinder can cause slow recovery and poor system performance.

What Happens to Existing Pipework, Pumps and Valves?

Existing pipework may be reusable, but it must support the required heat-pump flow rate.

Compared with a boiler system operating at a large water-temperature difference, a heat-pump system may require a higher water flow to transfer the same output. The installer should check:

Pipe diameter and equivalent length
Available pump head
Pressure drop through radiators, valves and filters
Thermostatic radiator valve behaviour
Bypass arrangements
Dirt and magnetic separation
Air removal
Hydraulic balancing
Minimum open circuit under zoning conditions

The existing system should be cleaned as required before the heat pump is commissioned. Strainers and magnetic separators should remain accessible for inspection and maintenance.

Monoblock R290 Installation Considerations

In an R290 monoblock system, the factory-sealed refrigerant circuit remains within the outdoor unit while water pipes connect the unit to the building.

The installer should consider:

Product-specific safety clearances
Nearby doors, windows, drains and ignition sources where applicable
Free outdoor airflow
Service access
Sound impact on the property and neighbours
Stable mounting and vibration control
Defrost-water collection and drainage
Protection from snow, ice and flooding
Freeze protection for external water pipework
Correct insulation and weatherproofing
Electrical isolation and protective devices

R290 is propane and is classified as a flammable refrigerant. Installation, transport, service and product placement must follow the applicable EXINDA manual and local requirements for the exact model and market.

How Should Outdoor Water Pipes Be Protected From Freezing?

Because a monoblock unit carries water outdoors, freeze protection must be planned for both normal operation and power-loss conditions.

The appropriate method depends on the project and may include:

Correct pipe insulation and weather protection
Short, well-routed external pipe runs
Automatic circulation and anti-freeze control
Suitable glycol concentration where permitted by the product and system design
Freeze valves where appropriate
Backup power or emergency planning in vulnerable locations
Correct installation of external sensors and valves

Adding glycol affects heat transfer, viscosity, pressure drop and pump selection. The concentration and resulting performance correction should therefore be considered during hydraulic design rather than added without calculation.

Why Commissioning Matters in Boiler-Replacement Projects

A correctly selected heat pump can still perform poorly if the system is commissioned like a traditional boiler.

The installer should verify and record:

System pressure and water quality
Clean strainers and unrestricted flow
Flow rate through the heat pump
Entering and leaving water temperatures
Heating-curve settings
Zone operation
Pump and valve control
DHW priority and recovery
Supplementary-heater settings
Defrost-water drainage
Active alarms and sensor readings
Customer controller settings

The heating curve should be adjusted to provide the lowest practical water temperature while maintaining comfort. Excessively high fixed setpoints can reduce efficiency and increase cycling.

When Is Direct Boiler Replacement Not the Best First Step?

Further building or system work may be needed when:

No reliable heat-loss calculation is available
The building envelope has severe uncontrolled heat loss
Required radiator temperature remains excessively high
Most radiators are undersized at heat-pump temperatures
The electrical service cannot support the proposed system
There is no suitable outdoor location
External water pipework cannot be adequately protected
The hydronic system cannot maintain minimum flow
Domestic hot-water requirements have not been assessed
Local planning, sound or safety requirements cannot be met

In these cases, the installer may first improve insulation, resize emitters, upgrade electrical capacity, redesign the hydraulic system or evaluate a staged hybrid approach.

How EXINDA Supports Boiler-Replacement Projects

Project stage	EXINDA support
Initial evaluation	Review of application, climate, heat load and required water temperature
Product selection	Model-specific capacity and performance review
System preparation	Technical datasheets, dimensions and connection information
Hydraulic coordination	Product-side flow and integration information
Documentation	Manuals, wiring diagrams, controller guides and applicable certification files
Commissioning	Product setup and controller guidance
Troubleshooting	Fault-code review and product-side technical support
After-sales planning	Spare-parts identification and service coordination
Market development	Product training for distributors and installer partners

Certification must always be confirmed for the exact model. Applicable EXINDA R290 products are supported by CE, ErP and Heat Pump KEYMARK documentation according to the certified model scope.

Review the EXINDA R290 heat pump range for Europe or the dedicated R290 heat pump supplier page for current platform information.

Frequently Asked Questions

Can an R290 heat pump directly replace a gas boiler?

Yes, if the heat pump can meet the building heat loss at the required outdoor and water temperatures and the radiators, hydraulics, electrical supply and domestic hot-water system are suitable. A site-specific assessment is required before final selection.

Can the existing radiators stay in place?

They can remain if their output at the proposed heat-pump flow and return temperatures meets each room’s design heat loss. Some projects require only selected radiators to be enlarged.

Should the heat pump match the boiler’s rated output?

Not automatically. Boilers are often oversized. Heat-pump selection should start with a design heat-loss calculation and model-specific performance at the project’s outdoor and leaving-water temperatures.

Can an R290 heat pump produce high-temperature water?

Selected R290 models can support higher leaving-water temperatures, subject to the published operating envelope. Efficiency generally decreases as the required water temperature increases, so the system should use the lowest practical design temperature.

Is a buffer tank required for every boiler replacement?

No. It depends on minimum system water volume, minimum flow, zoning, compressor modulation, defrost requirements and whether hydraulic separation is needed.

Can the existing domestic hot-water cylinder be reused?

Only if its heat exchanger, storage volume, sensor arrangement and recovery performance are suitable for the proposed heat-pump operating temperatures.

Is glycol required in a monoblock system?

Not in every installation. Freeze-protection design depends on climate, pipe routing, product requirements and local practice. If glycol is used, its effect on flow, pressure drop and heat transfer must be calculated.

Can the existing boiler remain as backup?

Yes, a bivalent or hybrid design may retain the boiler for peak load or defined operating conditions. The hydraulic arrangement and control sequence must be engineered clearly.

Does EXINDA support installers with product selection?

Yes. EXINDA can review project location, calculated heat load, required water temperature, emitters, electrical supply and application information against the relevant product data.

Are all EXINDA R290 heat pumps Heat Pump KEYMARK certified?

Certification is model-specific. The exact capacity and configuration must be checked against the applicable certificate scope before certification is referenced in a quotation or project document.

Request an R290 Boiler-Replacement Assessment

If you are an installer, heating contractor, distributor or project company evaluating an R290 heat pump for boiler replacement, please provide:

Company name and country
Project city or postcode
Building type and heated floor area
Calculated design heat loss
Outdoor design temperature
Existing boiler fuel and rated output
Existing radiator, underfloor-heating or fan-coil system
Current and proposed flow/return temperatures
Domestic hot-water requirement
Available electrical supply
Hydraulic schematic, if available
Required quantity and project schedule

EXINDA will use this information to help identify the appropriate product data and next technical steps.