Understand the building first
Insulation, roof construction, glazing and air leakage vary widely between garden rooms. A well-insulated office has different requirements from a highly glazed summer room or a converted outbuilding.
The survey should consider when the room is occupied and whether it needs cooling, heating or both. Computers, exercise equipment and several occupants can add meaningful heat even in a small footprint.
One system for year-round use
A reversible split system can cool the space in summer and provide responsive heating when the outdoor temperature falls. Model performance should be checked against the room construction and the manufacturer operating range.
Schedules and app controls can be useful where the room is separate from the house, allowing comfort to be prepared before use without conditioning an empty space all day.
Keep the installation practical
The outdoor unit may be close to boundaries, seating or neighbouring properties, so sound, airflow and access require thought. Condensate drainage and the electrical supply should be agreed before installation.
Pipework can often be kept short, but the neatest route still needs suitable clearances and service access. The quotation should identify any electrical or groundwork outside the normal installation scope.