Assess the home you have now
A design assessment needs room-level information about dimensions, construction, windows and likely heat loss. An EPC can be useful background, but its overall rating is not a room-by-room heating design. Tell the designer about additions, draughty rooms and changes you intend to make.
Separate confirmed facts from assumptions. If an old wall's build-up is uncertain, the proposal should recognise that uncertainty. If roof or window work is already planned, decide which version of the building the heating design is meant to serve. Otherwise, two individually sensible projects can work towards different assumptions.
Find out what can stay
Existing radiators are assessed against each room's heat requirement at the proposed water temperature. Some may be suitable; others may need changing. Their appearance or age alone cannot settle the decision. Pipework and the movement of water through the system also need checking.
Ask for the reason behind each proposed alteration. A recommendation to change one bedroom radiator is different from a plan to replace the entire distribution system. Understanding that distinction helps you compare proposals and decide where disruption is justified.
Make space a design question early
Include hot-water storage, equipment access and routes for pipes and cables in the first conversation. Moving from a combi boiler can introduce a new storage requirement. Measure potential spaces rather than assuming a cylinder will fit because a cupboard looks generous.
For the outdoor unit, consider the usable space around it as well as the unit itself. Airflow, drainage, maintenance access and the effect on neighbouring rooms matter. A neat enclosure is not automatically a suitable solution. The location should be assessed before the garden or interior layout is finalised.
Protect the features you want to keep
Mark the floors, joinery, plasterwork and other features you want the design to respect. Plan service routes deliberately, including where they become visible. In a listed building, alterations to the fabric or historic services may need consent even when the new equipment is inside.
Underfloor heating is an option, not a prerequisite for a heat pump. It can suit a floor already being rebuilt, but creating it within a finished or historically significant room is a different decision. Radiators and other suitable emitters deserve consideration before committing to lifting floors.
Agree the sequence before the specification
Bring together the household's priorities, building work and heating choices. Which rooms must remain usable? What can happen before decoration? Which decisions depend on permission or further investigation? These practical questions help establish a realistic sequence.
Also discuss how you expect to use the heating. A suitable heat-pump system may operate for longer periods than the short boiler bursts you are used to. Commissioning and an understandable handover matter, as do realistic explanations of operating costs and the assumptions behind them.