An outdoor unit above a neighbour's window puts noise, warm discharge in cooling, and defrost water in heating at the one place they will notice. It can be unacceptable even when it is the shortest pipe run from your indoor unit. This page will not invent a minimum distance in metres. Follow the Planning Portal heat pump conditions, the manual's clearances, and the manufacturer's noise data, and prefer another elevation when one exists. Clear water dripping in heating is normal defrost. It should not become their problem. An oil sheen is not normal.
Warm air, hum and water at their cill
The fan is a steady noise, and a wall bracket can add vibration. In cooling, the discharge is warm air. In heating, the base sheds defrost water that can blow onto a cill or a pane below. A bedroom window is the sensitive case. A blank gable is a different conversation. Noise, warm air and drip are the impacts. No universal metre separation is stated here. Another elevation is often the better design. Planning Portal conditions still apply.
Talking to the neighbour first is decent and does not replace the rules. A refusal is a reason to look at another wall before you buy the kit.
Mounts, a drain on your side, and a wall you can service
A ground stand away from the window, a different facade, or a model with a lower noise figure can change the impact. Anti-vibration mounts help structure-borne hum. They do not delete airborne noise into an open window a short distance below. Route defrost water to a drain or a soak that is on your side, so the heating season does not mark their glass. Do not cover the unit in winter to keep the drip in. It has to breathe, including during defrost.
On a block, the wall may not be yours. The lease and the freeholder come before the bracket. Section 20 is a separate process when the landlord is doing qualifying works for the building. Your single unit is usually a consent question. Check current consultation thresholds with the Leasehold Advisory Service only if the landlord is billing the block. F-gas installation and a service route still matter. A unit nobody can reach except by leaning from your window is a poor design, whatever the neighbour thinks.
Frequently asked questions
Is there a legal minimum distance above a neighbour's window?
This page will not invent one. Use the Planning Portal heat pump conditions, the noise data for the model, and the manual. If another wall works, use that.
Is drip onto their window normal?
Defrost water in heating is normal for the unit. Letting it fall on a neighbour's window is a siting failure. Route the water on your side. Oil on the water is not normal.
If my neighbour agrees, can the unit go there?
Their agreement helps the relationship. Planning rules, the lease and the manual still apply. Get those right as well. A friendly yes does not authorise a unit that fails a planning condition.
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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.