Survey a brick outbuilding as its own shell: solid or cavity, damp or dry, powered or not. The decision is a single split for the way you use it, fed from a real supply, with condensate taken to a drain that may not exist yet. It is not a log cabin and it is not a spare bedroom upstairs. Pipes back to the house outdoor unit usually fail on length, and a new indoor unit on that outdoor unit is usually not a mix-and-match. An F-gas certified company installs the pair at the outbuilding if planning allows the spot.
Solid brick or a proper cavity, seen before the quote
Victorian outbuildings are often single-skin solid brick, damp at the base, with a bitumen roof. A modern garden office in brick may be a proper cavity with insulation. Those are different duties and different drills. A solid wall is a core through the full thickness and a finish, not a cavity-tie detail. The survey has to see which one you have before the quote is fixed. Use decides the setpoint. Say which, because an afternoon office and a short workshop visit are not the same duty. A shut, uninsulated shell will still be harsh at the edges whatever the badge on the unit. Say this is a brick outbuilding, not a room in the house, what you use it for, how far it is from the house, and whether it has its own consumer unit. Photos of the wall thickness if a window reveal shows it, the roof, the outdoor side, and any damp, are the set. Confirm insulation and damp before sizing.
A socket on a long cable, and a pair on this building
Many brick outbuildings have a single socket on a long cable, or nothing lawful at all. A dedicated circuit is an electrician's confirmation, not a guess at cable size from this page. If there is no spare capacity at the house end, that work sits in front of the split. The outdoor unit can go on the outbuilding wall if the brick is sound and the neighbour is considered. In England, check Planning Portal conditions. A building at the boundary makes noise the main test. Planning permission for the outbuilding's use is a separate question from the heat pump. The clean job is a matched pair on the outbuilding, commissioned there. Keep the outdoor unit on this building if the length back to the house fails. Ask for a pair at the outbuilding, with model codes, solid-wall or cavity drill called correctly, and a condensate route.
As a 2026 illustration, the split is often in the low thousands including VAT when the wall and a basic supply already exist. A new supply and a damp-related lining are the larger unknowns, and they should be named rather than folded into a hopeful lump sum. Supply and drain are often missing. Energy Saving Trust describes reversible air-to-air units as heat pumps, which is why heating mode is a separate question from the cooling visit.
Frequently asked questions
Can I connect the outbuilding to the house outdoor unit?
Only if the pipe length and height are inside the limit and the indoor unit is a listed combination. Across a garden, that is rare. Price a pair on the outbuilding. A multi-split on the house does not reach a building at the end of the garden inside normal pipe and height limits. Measure before anyone suggests it. Ask them to confirm the house system cannot reach it if someone has already suggested that.
Will cooling a damp brick shed make the damp worse?
Cooling a wet single-skin wall can mark cold surfaces. Sort drainage and a lining if the building is still a damp store. The split's own condensate must not add to that water.
Does a brick wall need cavity ties for the pipes?
Only if there is a cavity. Solid brick is a core drill and a finish. The survey should say which wall you have so the quote does not copy a cavity detail.
Where does condensate go if the outbuilding has no gully?
Condensate needs a gully, a soakaway or a pumped line. Dripping down solid brick onto a dirt floor is not a design. Supply and drain are often missing, and both belong on the quote.
Does a home office in the outbuilding need a different duty from a workshop?
A home office occupied all afternoon needs the glass and the roof counted. A workshop you visit for an hour is a weaker reason to spend the money. Say which before the kilowatt is chosen.
Is heating mode relevant in a brick outbuilding?
Heating mode matters if you work there in March and the brick stays cold. Energy Saving Trust describes reversible air-to-air units as heat pumps. The outdoor unit still has to pass Planning Portal conditions, and a boundary location makes noise the main test.
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How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.