How Long Does an Air Conditioner Takes to Cool a Room?


I wonder how long does an air conditioner takes to cool a room? So, I ran an experiment to find out.

A routinely used 1.5 HP split wall-mounted inverter air conditioner takes 11 minutes to cool a 170 sqft room to a comfortable level at maximum fan speed and a temperature setting of 24°C. It takes 38 minutes for the 1.5 HP air conditioner to cool the 170 sqft room from 30°C to 26°C while reducing the room's relative humidity from 75% to 52%.

At what temperature and relative humidity does a person feel comfortable is subjective. How fast an air conditioner can cool a room is depending on the conditions of the air conditioner, the room, and the outside temperature. Following I outlined all the conditions that I've set in my experiment.

Air Conditioner and Room Size in the Experiment

I'm using the Daikin inverter wall-mounted 1.5 HP air conditioner. I've been using it for three years. Here is the spec. sheet:

As an HVAC engineer, of course, I size the air conditioner myself. I'd selected this air conditioner model based on the calculated cooling capacity required for my bedroom. My bedroom layout as below:

The total area of my bedroom is 170 sqft with a ceiling height of 10 ft (measured from finish floor level).

Most residences in Malaysia have a standard ceiling height of about 9 to 10 ft.

FAQ: Does ceiling height affect air conditioning?

Ceiling height is one of the factors that affect both the size of an air conditioner and the time required for an air conditioner to cool a room. A high ceiling room contains more air volume and thus, contains more heat and moisture compared to a room with a standard ceiling height. Therefore, high ceiling rooms generally required more cooling capacity. Besides, an air conditioner required a longer time to cool a high ceiling room.

Although the ceiling height affects the time required for an air conditioner to cool a room, it is not as significant as other factors such as room size and window area. In addition, if your ceiling is very high, you can always install your air conditioner at an optimum height.

Curious about: Why Air Conditioners are Placed at a Height?

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It is important for me to show you the window size because it significantly affects the time required for an air conditioner to cool a room. It's not hard to understand that a room with large windows allows more heat to enter the room and therefore, takes a longer time to cool the room with the same air conditioner.

Here is the size of my windows:

FAQ: Do curtains keep a room cooler?

Curtains reflect a certain percentage of sunlight and prevent it from entering into a room, reducing the heat gain from the windows and keep the room cool. Keeping the curtains closed, especially on the side where strong sunlight is coming in, not only keeps a room cooler but also helps to reduce the energy usage of the air conditioners.

Also, some people suggested that dark color curtains absorb more heat while light color curtains reflect more heat. Thus, light color curtains will keep your room cooler. But, I've not tested it.

Setting the Conditions for My Experiment

There are many factors affecting the time required for an air conditioner to cool a room. In order for my test result to be relatable, I've set as many conditions as I practically can.

Air Conditioner Cleanliness

The fan blower of my air conditioner indoor unit is considerably dirty (full of dust) but the air filter is relatively clean. Because of the dirty fan blower, the air conditioner is blowing air at inconsistent flow. Sometimes more, sometimes less. I can hear different noise levels when the airflow rate changes. I should definitely service my air conditioner after this.

In addition, the outdoor unit of my air conditioner is well ventilated. I don't have any forced ventilation, just natural ventilation and the spacing is sufficient.

Doors, Windows and Shading of the Room

Both of my bedroom and toilet doors are closed. All windows are closed and the curtains I opened about 50% to let sunlight come in which I believe most people do so. Moreover, the door and windows gaps also shown as some people may want to compare them.

Weather and Outside Temperature

Obviously, the outside temperature affects the test result. If it's raining, the outside temperature is lower, the room also cooler, so, it takes a shorter amount of time for the air conditioner to cool the room. Hence, it is crucial that I record the outside temperature and humidity before I turn on the air conditioner.

Relative humidity is 79% and temperature is 30°C

Throughout my experiment, the weather is quite consistent. I did observe it and there was no sudden change of weather except for a brief period of cloud sky.

Read about: The Effects of Outside Temperature on Air Conditioners

Fixed Variables

It is important to fix certain variables during the experiment so that they don't affect the result. Below are the things that remain unchanged throughout the experiment:

  • All doors and windows were not opened throughout the experiment.
  • Curtains remain opened at 50% except for the last part of the experiment.
  • Remote controller set at cooling mode and temperature setting at 24°C.
  • One person in the room (me) with one laptop only.
  • Typical brick wall room located on the first floor.
  • No ceiling fan.
  • No swing.

Procedures and Time Stamps of the Experiment

Everything is set, I begin my experiment and I recorded it as follow:

  1. Clock 11.47am – RH 75%, 30°C – Turn on the air conditioner with TURBO MODE to test the performance of the air conditioner at full blast and also, this is what I'll normally use my air conditioner.
  2. Clock 11.58am – RH 68%, 28°C – I feel comfortable – It doesn't feel like I'm in an air-conditioned room but it certainly feel comfortable already due to the lower humidity (no more feeling sticky).
  3. Clock 12.07pm – TURBO MODE is off, I switch to maximum fan speed – I let it continue to blast at full fan speed.
  4. Clock 12.25pm – RH 52%, 26°C – I now feeling like I'm in an air-conditioned room – At this temperature, the coldness hits but not as cold as when I go in a shopping mall.
  5. Clock 12.39pm – RH 47%, 26°C – I set the temperature to 16°C – I tried to push the temperature lower and keep the air conditioner running at full capacity.
  6. Clock 12.47pm – RH 45%, 25°C – I close all curtains – I thought it might help to further lower the temperature.
  7. Clock 01.09pm – RH 45%, 25°C – Both RH and temperature didn't budge.

See the cut video as follow:

Result

So, how long my air conditioner takes to cool my room? Here is the result:

TimeTime PassedRelative Humidity & TemperatureMy Observation
11.47am0minsRH 75%, 30°CSlightly hot, sticky, not very comfortable
11.58am+11minsRH 68%, 28°CComfortable, not humid / sticky, not cold
12.25pm+38minsRH 52%, 26°CComfortable, slight cold, no jacket needed

My Takeaways

My experiment and test result may not be perfect but it is a good reference, especially for an air conditioner that is not brand new and perfectly clean. I believe it simulated the conditions of most people. Furthermore, this experiment also demonstrated the result of an “almost worse case” scenario because of the below-average cleanliness of the air conditioner.

Besides, the result of the experiment also indirectly indicated that the sizing of the air conditioner is fair (not undersize or oversize) for the room. However, it does not mean that the air conditioner for a 170 sqft room should be all sized the same way since there are many other factors to be considered when sizing an air conditioner.

This experiment also serves as a reminder for everyone that air conditioners must be cleaned regularly to maintain performance and prevent high power consumption. Whenever I've done servicing the air conditioner, my bedroom usually reaches 24°C within 30 minutes.

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Yu Chang Zhen

I enjoy working on air conditioners and ventilation fans because Malaysia is a very hot country.

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