Ducted and concealed air conditioning in London

Ducted systems are popular in high end refurbishments in Kensington, Chelsea, Hampstead and Richmond, where owners do not want a white box on a decorated wall or near original cornicing. They also suit basement conversions, where ceilings are being built new, and loft rooms where a void sits behind a knee wall. The unit itself sits in a dropped ceiling over a corridor, bathroom or cupboard, and short insulated ducts carry air to linear or square grilles in each room.

Ducted units need space. You usually need:

• a ceiling void deep enough for the unit, often in a corridor or bathroom with a lower ceiling
• a return air path back to the unit so air can circulate
• an access hatch to reach the filter and fan for servicing
• a condensate drain with a proper fall, or a pump
• a route for refrigerant pipes to the outdoor unit

In a period house with shallow joists, that may mean lowering one corridor ceiling. That is why the system needs to be designed at the start of a project, not added at the end.

The indoor part is hidden, but the outdoor unit still needs a legal, quiet position, and the same planning rules apply as for any heat pump or air conditioner. In a listed building, cutting into historic ceilings and walls needs listed building consent as well as planning. In central boroughs the noise at the nearest neighbour's window is often the deciding factor, so we choose the outdoor unit and its spot early and share the figures with your architect.

Hidden does not mean maintenance free. Filters need cleaning, the coil and drain tray need checking, and the condensate drain must stay clear or water will find its way into your new ceiling. A good access hatch and a regular service plan protect the decoration as much as the system. See our servicing page for what a service includes.

On a refurbishment we need to be involved at the drawing stage. The architect needs to know where bulkheads and dropped ceilings will go, the structural engineer may need to approve notches or holes in joists, and the builder needs to know when first fix pipework and ducts must be in. Electrical first fix also has to include the power supply and control cable runs. Getting this into the programme early avoids the most common problem with ducted systems, which is discovering at second fix that there is no room for the unit or no access to service it.

The refrigerant side of a ducted system is the same as any split, so the work must be done by an engineer with an F-gas qualification working for a certified company, and the new electrical supply must meet Part P. Ask for the commissioning record at handover and keep it with your building paperwork.