CFM Calculator for AC Systems in the UAE

It is the standard design figure for air conditioning, and it is not arbitrary.

A cooling coil has to have air passing over it fast enough to carry the heat away. If air moves too slowly, the coil keeps getting colder until moisture on it freezes, and then almost no air gets through at all.

Around 400 cubic feet per minute of air for every ton of cooling keeps the coil in the range it was designed for.

The figure is adjusted for what you want the unit to do. Lower, around 350, makes the coil colder and pulls more water out of the air, which suits a humid coastal climate. Higher, around 450, moves more air and cools without drying as much.

For most UAE installations, somewhere between 350 and 400 is the sensible range, because taking humidity out is a real part of the job here.

When a ducted system stops cooling well, most people assume the gas is low or the unit is tired. Very often it is neither. It is air.

The chain runs like this. A dirty filter, a crushed flexible duct or a blocked return grille means less air over the coil. Less air means the coil runs colder than designed. A colder coil ices up. Ice blocks the airflow further, which makes it colder still.

By the time somebody looks at it, the indoor unit is a block of ice, there is water dripping from the ceiling, and the room is warm.

The frustrating part is that the fix is usually free or close to it: wash the filter, clear the return, straighten the duct. But if it gets diagnosed as low gas, somebody adds refrigerant to a system that did not need it, and the real problem is still there.

So when a ducted system underperforms, check the air path before anything else.

One ducted unit feeding four rooms does not give each room a quarter of the air, and it should not.

Each room should get air in proportion to how much cooling it needs. A west facing living room with a wall of glass needs far more than a small internal bedroom, even if the bedroom is closer to the unit.

That is what dampers are for. Each branch has an adjustable damper, and balancing the system means setting them so every room gets its share.

Almost no system in a home is ever balanced properly, which is why so many villas have one room nobody can sleep in during summer and another that is freezing.

The tool splits evenly as a starting point. If one room is always warm, the answer is usually a damper adjustment rather than a bigger unit.

In rough order of how often it is the cause.

You will meet three units for the same thing, and it is worth being able to move between them.

CFM is cubic feet per minute. It is what fans, grilles and diffusers are labelled with in the UAE.

Cubic metres per hour is the metric equivalent, and it appears on European equipment. One CFM is about 1.7 cubic metres per hour.

Litres per second turns up in some standards and specifications. One CFM is about 0.47 litres per second.

When you are comparing two products, check which unit each one is quoting before you decide one is twice the other. The tool shows CFM and cubic metres per hour side by side for that reason.