A window AC does something a split unit does not: it sits in the opening, so the gap around it leads back into your room. Add the condensate drip — a reliable water source through the hottest months — and it becomes one of the most attractive spots on a flat.
At a Glance
The projecting body of a window AC gives a flat shelf at exactly the height birds like, with the window reveal sheltering it on both sides and the sunshade often covering it from above. It is a three-sided alcove with a floor.
Two things then make it better than any other spot on the building: the gap around the unit, and the water.
Nesting material ends up in your window recess
A window AC is rarely a perfect fit in the opening. There is almost always a gap around the casing, filled with foam, wood packing or nothing at all. Birds work into that gap, and unlike a split unit — where the cavity is against a solid wall — this one opens back toward the room.
That is how nesting material, feathers and mites end up on the inside sill. Sealing the gap properly is half the job here, and it is the half that most people skip because spikes on the outside feel like the whole answer.
A window AC sheds condensate through the summer, which is when open water is hardest for birds to find in a city. A unit that drips onto its own casing or into a tray below is supplying drinking water on demand, and birds will use a spot with water over an identical spot without it.
Where the drip collects rather than falling clear — a blocked drain, a sagging tray, a ledge below — fixing the drainage removes part of the attraction before anything is fitted.
| Location | What happens there | Fix |
|---|---|---|
| Top of the projecting body | The main perch. Flat, sheltered, at height. | Spikes across the full top |
| Gap around the casing | Nesting, and material works back into the room | Seal it properly |
| Support angle or frame below | Perch, and often the nest platform | Spikes on the angle |
| Sunshade above | Perch, then drop onto the unit | Spikes on the sunshade |
| Window sill beside | Continuation of the same ledge | See window sills |
| Grille bars around it | Perch every few inches | Spikes on the top rail |
Do not block the rear grille
Like any air conditioner, a window unit sheds heat by moving air through the back and sides. Spikes belong on the top and on the support frame — never across the intake or discharge grilles, and never wrapped in net. If it cannot breathe, it works harder.
Unlike a split unit on a high wall bracket, a window AC is at window height and reachable from inside. That makes it one of the few surfaces on this site where no external access is needed.
The top of a window AC is a wide, flat, inviting shelf and pigeons are the usual occupant. Pin height and spacing set for a heavier bird is what makes it unusable.
Fits: unit top, wide sunshades
Narrower base for the support angle, the frame and the grille top rail, where a wide strip will not sit flat.
Fits: support angles, frames, grille rails, adjacent sills
The main case. Flats and houses, one or two units each, and usually extended to the whole block once one flat has done it.
Older offices, hotels, guest houses and hostels with window units on every room. Bulk quantity, small per unit.
Site offices, cabins, security posts and staff quarters, generally specified with the rest of the block.
Three things together: a flat shelf on the projecting body, a sheltered alcove formed by the window reveal, and water from the condensate drip through the summer. Very little else on a building offers all three.
Because the gap around the casing opens back toward the room. Unlike a split unit, where the cavity is against a solid wall, a window AC's gap is a route inside. Sealing it properly is half the fix.
No. The unit needs airflow through the back and sides. Use spikes on the top and the support frame, keep the grilles clear, and seal the gap around the casing.
Not if they are on the top panel and the support frame and clear of the intake and discharge grilles. What does affect cooling is a nest packed into the casing, which is what this prevents.
Usually yes, and this is one of the few surfaces where that is true — a window AC is reachable from inside. Switch the unit off first, and check there is no active nest before you clear anything.
That drip is part of the attraction in summer. If it pools on the casing or on a ledge below rather than falling clear, clearing the drain removes some of the appeal before anything is fitted.
Yes. Give us the number of units and we will quote by total running metres — the quantity per unit is small but it adds up quickly across a building.
Send a photograph of the unit from outside, including the gap where it meets the window frame. We will tell you the spike metres and whether the gap needs sealing before anything is fitted.