Replacing a boiler with an air-to-water heat pump requires evaluating the entire system. The radiators can be retained, expanded, or replaced depending on the calculation. The goal is to achieve the desired comfort without requiring an unnecessarily high flow temperature.
The same radiator delivers less heat with warmer water.
The output depends on the difference between the average temperature of the water in the radiator and that of the environment. A catalog power only makes sense under its testing conditions. If that difference decreases, the heat that the emitter can deliver changes; it is not enough to count elements or measure the surface area of the dwelling.
The IDAE and AFEC guide on rehabilitation with heat pump study the integration with existing emitters. Their examples of radiators show why it is necessary to recalculate the emission with the new water regime. The curve or table from the radiator manufacturer should be used and compared with the demand of your room.
What the study must check before replacing the boiler
The installer needs to know about enclosures, windows, infiltrations, orientation, and design temperatures. A room that loses more heat may require a larger emitter even if the rest of the house is compatible. The study should combine thermal load per room, radiator output, flow rate, and equipment capacity under the expected outdoor conditions.
The Daikin's guidance on aerothermal energy and radiators insist on sizing. For its part, Vaillant explains the compatibility factors with radiators.These guides help to formulate the questions, but they do not replace the calculation of your property.
It is also necessary to distinguish between heating and domestic hot water. The accumulator, the demand for showers, and the regulation of DHW are part of the design. The external location, the interior space, and the electrical connection must be addressed in the study. Our guide on the operation of aerothermal energy explain the general system; the question here is how to adapt it to the existing emitters.
Conserve, expand or replace emitters: compare the alternatives.
| Alternative | What to check |
|---|---|
| Maintain the radiators | Sufficient power per room at the expected temperature and hydraulic condition of the installation. |
| Enlarge certain radiators | Available space and new power; it can solve the deficit of specific rooms. |
| Low temperature emitters or fan coils | Power, noise, supply and distribution; if cooling is sought, condensate design. |
| Improve insulation | Reduction of demand that allows operation with lower water temperature. |
Balancing and regulation are important in addition to the nominal power. A circuit that poorly distributes the flow can leave rooms cold. The Vaillant's explanation of hydraulic balancing distinguish the water distribution from a simple bleed: the adjustment requires knowledge of the system.
Conventional radiators should not be considered valid for cooling. If you also want cold, request a solution of emitters, pipe insulation, and condensation management designed for that service. The reversible capacity of the unit does not make all elements of the installation suitable for summer.
How to compare consumption without promising a fixed saving?
COP describes a operating condition; seasonal efficiency reflects a set of conditions. Water temperature and climate influence the outcome. The declared data must be compared for the relevant operating conditions and climate, including electrical support and auxiliary consumptions considered in the study. The explanatory documentation from Vaillant relate lower flow with higher efficiency; it does not establish the savings of any home.
Example of calculation, not forecast of your bill: If the useful annual demand were 10,000 kWh and the seasonal efficiency of the system were 3, the corresponding electricity would be approximately 3,333 kWh. If it were 2, it would be 5,000 kWh. These are two hypotheses to demonstrate the sensitivity of the calculation; the study must justify which one applies and what consumptions it includes. Then multiply by the effective energy price and compare maintenance and investment under the same scope.
What documentation should I request before making a decision?
Request a quote including thermal load per room, preserved or modified radiators, design water temperature, and exact model of the heat pump. It should explain capacity and performance under relevant conditions, regulation, domestic hot water, support, commissioning, and construction items. A total figure without this data makes it difficult to compare proposals and identify missing elements.
To assess your property, consult the Uniclima aerothermal serviceIf your radiators are already experiencing heating issues, first address the cause: replacing the generator does not guarantee correcting poor distribution.
Technical references
Consulted on October 7, 2026: IDAE/AFEC guide on energy rehabilitation with heat pump, Daikin guidance on radiators, and Vaillant documentation on compatibility, operation, and balancing, linked in each section. The values of the chosen model must be verified in its technical documentation.