Start with the rooms that already cause problems
Before discussing heat pump models, describe how your home is heated now. Note which rooms feel cold, which quickly reach the chosen temperature and whether their behaviour changes when doors are closed. This picture of daily life helps make a site visit useful. The fact that your current boiler can heat the house does not, by itself, prove that every radiator is suitable for a different way of producing heat.
Counting radiator sections is not enough either. A room with large windows, an internal room and one beneath the roof may have different requirements, even if they are the same size. The assessment needs to relate each room's heat demand to its heat emitter.
Water temperature changes a radiator's heat output
A radiator's heat output depends on its operating conditions. With cooler water, it may deliver less heat than the output stated for other temperatures in its catalogue. This makes it important to identify the type, dimensions and, where possible, the emitter's technical data sheet.
A clearly explained proposal should state the temperatures used to assess compatibility. Asking for that information is more useful than seeking a universal answer to whether old radiators will work. It may make sense to keep some, increase the size of others or replace only those in the rooms with the highest requirements.
Include planned home improvements in the calculations
If you are replacing windows or improving insulation, tell the installer before equipment is selected. The assessment should reflect the home you will have after the renovation. Choosing equipment based on its previous condition can leave the system poorly matched to its new requirements.
Prepare a simple plan and distinguish confirmed work from possible future changes. Include how each room is normally used: a home office occupied all day presents a different situation from an occasional bedroom. You do not need to arrive with your own calculations, but clear information will help the professional justify the proposed solution.
Check the distribution pipework too
Radiators are part of a circuit. The installer needs to assess the condition of the pipes, water circulation and the way individual rooms are controlled. Replacing only the heat source without examining the rest may leave imbalances that already existed with the boiler.
To prepare for the visit, gather photographs of accessible radiators and valves, along with any available documents. Do not dismantle valves or carry out pressure tests yourself. If one room has never worked properly, point it out specifically: it deserves a focused check rather than getting lost in a general description of the house.
Clarify what will happen in summer
Keeping radiators for heating does not mean those same emitters will provide cooling. If you also want cooling, the design should explain how it will be delivered and which additional components are required. That decision affects space, service routes and the scope of the work.
Before accepting a proposal, ask for a room-by-room summary: whether the emitter is retained or new, the service it will provide and the control you will use. This lets you compare options without assuming that an undefined result is included. Compatibility is demonstrated by a complete solution, not a general statement about the technology.
More common questions
Will I have to replace every radiator?
Not necessarily. Their output under the proposed operating conditions and each room's requirements need to be checked. The decision may differ from one room to another in the same home.
Can I decide based on floor area alone?
That is not enough. Insulation, windows and other openings, room location, and the characteristics of the emitters and circuit also matter.
Sources and technical reading
Some source documents are available in Spanish.