What is CFM in air conditioning?

CFM means cubic feet per minute. It is how much air is moving. Fans, grilles and ducts in the UAE are usually labelled in CFM, so it is the number you shop with.

How many air changes per hour does a bathroom need?

Around 8 as a starting point. Steam has to leave quickly, because moisture landing on walls and ceilings is what causes mould.

Does my air conditioner bring in fresh air?

Most split units do not. They cool and dry the air already in the room. Fresh air comes from windows, from an extract and supply system, or from a dedicated fresh air unit.

Why does my bathroom keep growing mould?

Almost always ventilation. The fan is too small, blocked with dust, ducted badly, or not run for long enough after a shower. Cleaning the mould without fixing that just delays it.

How do I convert CFM to cubic metres per hour?

Multiply CFM by about 1.7 to get cubic metres per hour, or divide by 1.7 to go back the other way. The tool shows both figures.

Is more ventilation always better?

No. In this climate every cubic metre of outside air you bring in has to be cooled and dried, which costs money. The aim is enough, not maximum.

HVAC Airflow Calculator

Room length

Room width

Ceiling height

Air changes per hour

How many times the whole volume of air is replaced each hour.

People in the space

Used to check the fresh air figure as well.

Your answer

Airflow needed

212 CFM

That is 360 cubic metres an hour.

Room volume: 60 m3
Air changes an hour: 6
In cubic metres an hour: 360 m3/h
In litres a second: 100 L/s
Per person: 106 CFM

Air changes are a design guide, not a regulation. Anything commercial should be checked against the rules that apply to that building.

HVAC Airflow Calculator for Dubai and the UAE

This tool works out how much air needs to move through a space. It is measured in CFM, which means cubic feet per minute, and also given in cubic metres per hour.

This is a different question from how much cooling a room needs. Cooling is about removing heat. Airflow is about changing the air, so the room does not get stale, damp or smelly.

It is used for extract fans, fresh air supply, kitchen hoods and ventilation in rooms that have no window.

What air changes per hour means

Take all the air in a room. Air changes per hour is how many times that whole volume gets replaced in an hour.

A room with 60 cubic metres of air at 6 air changes per hour needs 360 cubic metres of air moving through it every hour.

The higher the number, the faster stale air leaves and fresh air arrives. A kitchen needs a high number because it produces smoke, steam and smells quickly. A bedroom needs much less.

CFM is the same idea in different units: cubic feet per minute. One cubic metre per hour is about 0.59 CFM. Fans and grilles in the UAE are usually labelled in CFM, so that is the number to shop with.

Why ventilation matters in a sealed UAE home

Homes here are built and lived in to keep the heat out. Windows stay shut for eight months of the year, doors close behind you, and gaps get sealed. That is the right thing to do for the electricity bill.

The side effect is that air does not move on its own. In a cooler climate people open windows without thinking, and the house breathes. Here it does not.

Sealed air gets stale. Cooking smells stay, bathroom damp lingers, and the air feels heavy by the end of a day. In a bedroom with the door shut and two people sleeping, carbon dioxide builds up overnight.

Damp is the practical problem. A bathroom with a weak or blocked extract fan grows mould in the corners and along the ceiling every year, and no amount of cleaning fixes it while the fan is the real cause.

The air conditioner does not solve this. Most split units only recirculate the air already in the room. They cool it and dry it, but they do not bring any new air in.

Rough figures for different rooms

Common design starting points. A commercial space should be checked against the rules that apply to it.

Bedroom and living room
Around 4 air changes an hour. These rooms produce little moisture or smell, and people spend long quiet hours in them.
Bathroom
Around 8. Steam has to leave quickly or it lands on the walls and the ceiling, and that is where mould starts.
Kitchen
Around 15, and much more directly over the hob. Cooking makes heat, steam, grease and smell all at once.
Laundry
Around 10. A washing machine and a dryer put a lot of moisture into a small closed room.
Office
Around 6, but people are the driver here rather than the room. A meeting room full of people needs far more than an empty one.
Restaurant or gym
Around 20 and up. High occupancy, high moisture and high smell all at the same time.

Signs a room is not getting enough air

These come up constantly in UAE homes and they are all ventilation, not cooling.

Mould in the bathroom corners
Steam is not leaving fast enough. Either the fan is weak, blocked, or it is not being run long enough after a shower.
Cooking smells all evening
The kitchen extract is not pulling properly, or the hood is recirculating through a filter instead of ducting outside.
The room feels heavy in the morning
A closed bedroom with no fresh air supply. The air is cool but it is the same air it was eight hours ago.
Damp smell in a store room
No air movement at all. Small internal rooms with no window and no extract are the usual place this happens.
Condensation on cold surfaces
Moist air meeting a cold pipe or grille. More ventilation removes the moisture at the source.

Getting the airflow you calculated

A fan rated at 200 CFM does not necessarily move 200 CFM once it is installed.

That figure is measured with nothing in the way. In a real installation the air has to travel down a duct, round bends and out through a grille, and every one of those takes something off.

A long flexible duct with sags in it is the usual culprit in a home. So is a grille clogged with dust, which happens fast here.

The other half is where the air comes from. If a bathroom fan is pulling 100 CFM out, 100 CFM has to get in from somewhere. A door with a gap under it is usually enough. A tightly sealed door means the fan runs against a closed box and moves far less than it should.

So when you size a fan, allow some margin over the calculated figure, keep duct runs short and straight, and clean the grilles.

Questions people ask

What is CFM in air conditioning?: CFM means cubic feet per minute. It is how much air is moving. Fans, grilles and ducts in the UAE are usually labelled in CFM, so it is the number you shop with.
How many air changes per hour does a bathroom need?: Around 8 as a starting point. Steam has to leave quickly, because moisture landing on walls and ceilings is what causes mould.
Does my air conditioner bring in fresh air?: Most split units do not. They cool and dry the air already in the room. Fresh air comes from windows, from an extract and supply system, or from a dedicated fresh air unit.
Why does my bathroom keep growing mould?: Almost always ventilation. The fan is too small, blocked with dust, ducted badly, or not run for long enough after a shower. Cleaning the mould without fixing that just delays it.
How do I convert CFM to cubic metres per hour?: Multiply CFM by about 1.7 to get cubic metres per hour, or divide by 1.7 to go back the other way. The tool shows both figures.
Is more ventilation always better?: No. In this climate every cubic metre of outside air you bring in has to be cooled and dried, which costs money. The aim is enough, not maximum.

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