Shophouse Airwell Install: Heat Rejection Set the Position

An installation judged on whether it fits and whether the pipe reaches. In a shared space that assessment leaves out the deciding question.

By Team Snowflake | Updated 24 Aug 2026

Teaching case based on recurring Snowflake service patterns; identifying details are combined.

What gets specified

A further outdoor unit proposed for an airwell that already carries two, stacked at different levels. Space exists for it and the pipe route is straightforward. The existing units are reported to be performing adequately.

Setup: Gree Wall-mountedNew installShophouseSingapore River
Misread as: An installation that works on paper and leaves every unit in the shaft performing worse.
Check first: Intake air temperature at the units already discharging into the shaft

What the drawing does not show

Physical space is the easy question and the wrong one to stop at. A shaft removes heat only as fast as air moves through it, and that rate is fixed by the opening at the top and the building around it. Each unit adds heat to the same rising column, so what matters is the total already being rejected against what the shaft can carry. Measuring the air temperature at each existing intake shows how much of that budget has already been spent.

Adequate clearance for a third unit answers the physical question and not the thermal one.
Intake air at the existing units already above the outside temperature shows the shaft is warming.
A narrow opening at the top of the shaft limits how fast air can carry heat away.
A third unit adding to the same rising column would raise intake temperatures for all three.

Why it goes wrong

Air rises through a shaft at a rate the building sets, and every unit discharging into that column raises its temperature. Units higher up then draw air that has already carried heat from those below. The capacity of the shaft is shared and finite. An installation that is sound in isolation can push the total past what the space will carry, and the cost lands on the existing units as much as on the new one.

What the fix involves

The third unit is placed outside the shaft, or the shaft's airflow is improved before anything is added to it. Where neither is possible, the honest answer is that the position cannot take another unit, and saying so is better than installing one that degrades three. This is the check worth making on any shared shaft, light well or plant recess.

How to tell it worked

Intake temperatures at every unit in the shaft, before and after any change. The measure of success is that no unit is breathing warmer air than it was, not that the new one runs.

Before you sign off

A shaft's cooling capacity is shared and finite

Clearance answers whether a unit fits. It cannot tell you whether the space carries the heat.
Measure intake air at the existing units. Above outdoor temperature means the budget is already spent.
A unit added past that limit degrades everything already there, not only itself.

Questions this case answers

How many outdoor units can fit in a shophouse airwell?

There is no fixed number. The shaft carries heat away only as fast as air moves through it, and that rate is set by the building. Every unit discharging into the same column raises its temperature, so the capacity is shared rather than individual.

Is it bad to stack condensers one above the other?

It can be. Stacking makes each unit draw air that has already carried heat from those below. Measure the air entering each existing unit and compare it against the outside temperature: a meaningful gap means the shaft is already warming, and there is little headroom left for anything further.

Where can outdoor units go in a conservation shophouse?

Outside the shared shaft, or failing that, only where the shaft's airflow can be improved first. Inside it, all units suffer and the higher ones worst, because units above draw air that has already carried heat from those below. Adding a unit therefore lowers the performance of equipment that was working perfectly well.

Will I still be able to service an outdoor unit sitting in an airwell?

It depends on the position, and anything that improves the situation is building work rather than aircon work. Opening or enlarging the outlet at the top, adding mechanical extraction, or ducting one unit's discharge clear of the shaft can all increase what the space carries.

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