Mechanical assessment should include multi-room heat loads, home-office use, glazing on later extensions, and whether one outdoor unit can serve distant rooms without exceeding pipe-run limits. Access for a larger condenser on a gravel drive is usually easier than in a terrace, but screening, noise toward neighbours and condensate still have to work.
Conservation areas run from the town into several villages, including places such as Otford and Kemsing. If an outdoor unit would affect a protected building or street, check with Sevenoaks District Council before work starts. Installers can advise on typical siting on large plots, but they are not the planning authority.
For typical house rules, listed buildings and when to check with the council, see planning permission for domestic air conditioning. If the building is protected, the council decides — an installer can help you think about where the unit would go.