A side alley can take an outdoor unit when the passage is wide enough for the cabinet plus the manual's side and front clearances, the gate still works, and an engineer can service the panel. It fails when the discharge hits the opposite wall and short-cycles, or when bins, meters and a locked gate leave no access. Airflow and service access fail more often than how the unit looks from the street. Measure the alley. Do not invent a universal width. In England, Planning Portal conditions and the neighbour's windows still apply.
The opposite wall as a solid object
The opposite wall is a solid object. If the fan is closer than the manual allows, the unit cools or heats poorly and runs louder. Side gaps matter too: a coil pulled tight to your own wall is as blocked as one facing the neighbour's bricks.
Bins, a bike and a gate that opens inward
Bins, a bike, and a gate that opens into the gap all count on the day you actually use the alley. A tape measure on an empty Tuesday is not the operating width.
- Front clearance to the opposite wall is the usual fail.
- The gate, bins and meters have to coexist with the panel.
- There is no universal alley width on this page.
- Appearance is the lesser problem.
Sound between two hard walls
Alleys are sound channels. A unit that is quiet in a garden can be sharp between two hard walls, outside a neighbour's kitchen. Defrost water in heating is normal and needs a drain that does not ice the shared path. An oil sheen on that water is not normal. A shared alley or a right of way is not automatically yours to block. Check the deed and, in a terrace, talk to the neighbour before the bracket is ordered. Council noise powers sit in the background if the siting is careless.
A person standing at the panel
Coil cleaning and a breakdown visit need the panel open and a person standing there. If that means moving three bins and a neighbour's gate every time, say so on the price. F-gas commissioning needs the same space on day one.
A long run from the convenient alley
Pipe length back indoors still follows that outdoor unit's manual. A convenient alley on the wrong elevation can be a long, ugly run. Planning Portal heat pump rules are separate from the tape measure. A slimmer cabinet helps only if the remaining air gaps still meet the manual. The slimness does not delete the front clearance.
When the alley is the wrong wall
The alley is the wrong wall when the discharge hits the opposite wall inside the manual's front gap, when the gate and everyday clutter close the service panel, or when the only orientation that fits is one the manual does not allow. Facing the fan down the alley works only if the manual allows that orientation and the air can leave without short-cycling, while the service panel remains usable. The survey should test that, not assume it. There is no single width.
Core buying guides
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Related guides
Sources and further reading
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.