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Basic things to know before buying an Air Conditioner

The Air conditioner or AC is no more a luxury in India, it has become an essential item for comfortable living. Before buying an AC in India you should know some basic things about AC, how AC works and how to know the right size of AC to buy for the size of room. This page has tips to buy a good Air Conditioner.

The best place to see all models of Normal and Inverter AC available in India is the Amazon India website. This is the link to Amazon India website to see all models of AC with best discounted prices

An air conditioner removes heat from a room, it is pushing or pumping heat from inside the room to the outside. So the power of AC required for a room depends on the size of the room and how much heat is coming into the room. We give details below on how to calculate the size of an AC required for a room.

While removing heat from the room, the AC also reduces the humidity, filters the air of dust and allergens like pollens and makes living in the room comfortable. Some AC can do both heating and cooling and you should consider such an AC in places like Delhi, where the summers are very hot and winter is very cold.

What to look for when buying an Air Conditioner in India?

We start with the basics of Air conditioners or AC. The first thing to consider when buying an AC is to decide on what size of AC is required. The size of ACs are given in Tons. What is 1 ton in AC is the cooling power that is equal to what one ton of ice will cool the room. There are calculations to determine the ton of cooling required for room size as discussed below. Other most important things to know before buying an AC are how much power the AC consumes and how can the electric cost of running an AC be reduced.

In room AC units there are basically two types of home AC units: the window AC and the split AC and each of these types of AC can be a normal AC unit with a regular compressor and an inverter AC which has a special variable speed compressor. An inverter compressor adjusts the speed of the compressor according to the cooling needs of the room, and since an inverter compressor does not stop and start and run at full speed all the time, it saves upto 40% in power electric costs. This monthly saving in electric bill of an inverter AC pays for the extra cost of Inverter AC in about 2 years depending on the usage. Please see our dedicated page on inverter ACs which explains why the inverter AC is better.

Below we explain everything what we need to know about Air conditioners, like how to choose the right size AC unit, how to size an air conditioner for room size, top AC brands in India, which type of AC is best: inverter AC or normal AC, power saving and pay back period of inverter AC, etc. These topics are all covered below and we have arranged each topic in a clickable list below:

How an Air Conditioner AC works

An AC uses a refrigerant like Freon, which easily changes its state from liquid to gas and back at different pressures and at room temperature. When a liquid evaporates to a gas it absorbs heat and when it is compressed back into a liquid it give off heat. The evaporation of the AC refrigerant liquid happens in a copper coil called the evaporator and is on the inside of the room being cooled. A fan blows the room air over the evaporator coils and the air becomes cold in the room.

The AC compressor sucks the evaporated gas from the evaporator coils and compresses it. This makes the gas to condense into a liquid giving off heat which it absorbed from the room. The condensation of the gas into a liquid happens in a coil called the condenser placed at the back of the AC. A fan blows the outside air over the condenser coils and hot air is being blown out of the AC at the rear portion of the AC which is outside the room. So in effect the AC is pumping heat from inside the room to the outside.

An air conditioner, while cooling the room, also removes the humidity in the room. The comfort of a room depends both on the temperature and the humidity. To remove humidity from the room, the AC needs to work hard, because to condense the humidity in the air into water, the AC has to absorb all the latent heat of condensation of the humidity and that takes a lot of energy.

What is the meaning of ton in AC

The term ‘ton of cooling’ came to being from the time when ice was use to cool warehouses and houses. One ton of cooling is the rate of cooling available when one ton of ice melts over a period of 24 hours. When one ton of ice melts uniformly over a 24 hour period, it absorbs heat at the rate of 286,000 / 24 hours = 11,917 BTU/hour. This figure has been rounded up and the cooling capacity per hour of one ton of ice has been standardised to be equal to 12,000 BTU/Hour. So a one ton air conditioner has 12,000BTU of cooling in one hour, the same amount of cooling as if you had one ton of ice kept in the room.

The British thermal unit or BTU is the de-facto industry standard for measuring heat or cooling. One BTU is the amount of heat required to heat or cool one pound of water by one degree Fahrenheit. In metric terms one pound of water is about 454 grams and one degree Fahrenheit is equal to 0.5556 degrees centigrade and one BTU is equal to 252.2 calories.

Split AC vs window AC, which is best

To know whether the split or window AC is better we will first compare the main differences between Split AC and Window AC. The following are the advantages and disadvantages of split AC over window AC:

1. Split AC is silent compared to a window AC

In a split AC unit, the noisiest parts of an AC unit, that is the compressor and condenser cooling motor and fan are outside the room and so a split AC unit is much quieter than a window AC unit. To install a window AC unit the wall has to be broken to make a big hole to fit the window unit on the wall, whereas for the split AC unit you just need a small 5 to 7 cm hole to be drilled in the wall to connect the indoor and outdoor units of the split AC.

2. Power consumption difference between window AC and split AC is negligible

Power consumption difference between window AC and split AC is so small that it can be considered to be equal. Many are under the impress that a window AC consume more electricity, but the answer to ‘does window AC consume more electricity? is ‘No’ for all practical purposes. Initial cost of a split AC unit will be more expensive and installation costs of a split AC are also more expensive. Many building owners do not allow window ACs to be fitted due to aesthetic reasons and the fear that it may weaken the structure of the building itself, but there is no such problem with split AC units.

3. Advantage of window AC: it allows constant fresh air supply in the room

One major advantage window AC has over split AC is that the window AC can allow fresh air to enter the room and the amount of fresh air entering the room can be adjusted. In a split AC there is no means of constantly having a little fresh air come into the room. The only option to let fresh air into the room is by opening a window.

AC power consumption, monthly electric bill for AC

The bulk of the electric power required by an AC is to compress the refrigerant gas into liquid. How much electricity is required by an AC per hour depends on a lot of factors like the size of the AC, size of the room, the heat load in the room – whether the room has sunlight falling directly on its roof or walls, how many glass windows which allows radiant heat to enter the room, etc.

The power consumption of a 1 ton AC in a middle floor bed room of a flat, will be about 1.33 Kilo Watt Hour or 1.33 unit of electricity per hour during the night. This is a very general figure and the actual may vary by 25% plus or minus depending on outside temperature, insulation factor of the walls and so many other factors. This is how we arrive at this figure as follows

Monthly electricity cost for AC calculation

A one ton AC draws 10 Amps at 220 Volts while its compresser works (this is about the averqage for a non-inverter 1 ton AC) and only 2 Amp when compressor is not working.

The compressor works for 50% of the time the AC is on (depends on outside temperature and how well the room is insulated)

So while compressor works it is using 10×220 watts = 2.2 Kilowatts and works for half an hour in every hour
So energy consumption by the compressor is 0.5×2.2 = 1.1 Kilo watt hour or 1.1 unit per hour cost of running AC.
Energy consumption when compressor not working is 0.5x2x220 = 220 watts =0.22 KWHrs.
So total consumption per hour of a 1 ton AC is 1.1+0.22=1.32 Kilowatt Hours or units per hour.

If the AC is on for 9 hours a day, the power consumption per day will be 1.32×9=11.88 or say 12 units per day
So in a month a 1 ton AC working 9 hours every day will consume 12×30=360 units of electricity. If electricity costs Rs.5- per unit, your AC monthly electricity bill will be about 360×5=Rs.1800- per month.

What is AC star rating in India

The star rating of an Air conditioner in India is a measure of the energy efficiency of the AC. Star rating of an AC is based upon the EER (Energy Efficiency Ratio) of an AC. EER is defined as the cooling obtained per unit of electric power. So EER is obtained by dividing the cooling capacity by the power consumed.

In India the star rating is from the lowest one star for which the EER should be between 2.7 and 2.89 as shown in the table below. For the highest 5 star rating the EER should be a minimum of 3.5.

To show how an AC is star rated let us take an example of a 1 ton AC. 1 ton of cooling is 12,000 BTU per hour. One BTU converted to cooling Watts is 0.2937. So one ton cooling is 12,000×0.2937=3524.4 watts. Assume this AC uses 1000 watts of power, then the EER of this AC will be 3.524 and the AC will be classified as a 5 Star rated AC.

EER (Energy Efficiency Ratio) required for Star Rating as set by India BEE (Bureau of Energy Efficiency)

Star RatingMinMax
1 Star ★2.702.89
2 Star ★★2.903.09
3 Star ★★★3.103.29
4 Star ★★★★3.303.49
5 Star ★★★★★3.50

There have been several changes in the star rating of air conditioners in India, mainly due to the increased efficencies of the newer inverter ACs. We have pages explaining what new star rating of ACs in India mean and also how much more monthly electric bill you can save by buying a 5 star inverter AC instead of a 3 star inverter AC.

AC for room size in tons

To choose the right AC ton size for a room size there are many tables and websites which help you to make that decision. A good online AC ton calculator  is provided by LG on their website.

We also reproduce below a table on the correct tonnage of an AC for a room size as provided by ‘Energy Star’ the world’s leading authority on matters of efficient use of electricity. There is no point in buying a larger capacity AC than what is required according to the size of the room. We quote below from the Energy Star website, the worlds leading authority on matters of efficient use of electricity.

“Many people buy an air conditioner that is too large, thinking it will provide better cooling. However, an oversized air conditioner is actually less effective — and wastes energy at the same time. Air conditioners remove both heat and humidity from the air. If the unit is too large, it will cool the room quickly, but only remove some of the humidity. This leaves the room with a damp, clammy feeling. A properly sized unit will remove humidity effectively as it cools.”

The Energy Star recommended size of AC unit required for size of room in square foot or Metersis given below

Room Size
Square feet
Room Size
Square meter
AC Capacity
AC TonRound-off
100 up to 1509.3 to 13.95,0000.40.75
150 up to 25013.9 to 23.26,0000.50.75
250 up to 30023.2 to 27.87,0000.60.75
300 up to 35027.8 to 32.48,0000.70.75
350 up to 40032.4 to 379,0000.80.75
400 up to 45037 to 41.610,0000.80.75
450 up to 55041.6 to 50.912,0001.01
550 up to 70050.9 to 64.814,0001.21
700 up to 1,00064.8 to 92.618,0001.51.5
1,000 up to 1,20092.6 to 111.221,0001.81.5
1,200 up to 1,400111.2 to  129.823,0001.92
1,400 up to 1,500129.8 to 139.124,0002.02
1,500 up to 2,000130.1 to 185.630,0002.52.5
2,000 up to 2,500185.6 to 232.134,0002.82.5

Note the following:

  1. If you live in an apartment building or a 2 story house, and there is room above your roof, and also if no direct sunlight falls on your outside facing wall, then you can choose a lower capacity AC.
  2. If the roof of your room is exposed to sunlight, then you need a higher capacity AC and the power consumption will be high. In the longer run it would be cheaper to build a shade over the roof with aluminium sheeting. Or you can insulate the roof with Thermocol or other insulating sheets.

Best AC model in India, List of best AC brands in India

We provide below a list of manufacturers Airconditioners in India with links to their websites. All are well know AC brands in India and you can choose the best AC model in India fram any of these famous AC brands in India.

Advantage of Online buying of Home Appliances

Whatever Home Appliance you plan to buy, it is best to first do an online research about all available types and models on the leading online retailers in India, namely Amazon, Flipkart and Snapdeal. The advantage of first doing an online research about products you plan to buy is that you get to see all the available models of the product and you get to compare prices online. After this you can go around to the showrooms and do window shopping.

You should then decide to buy from the cheapest and most reliable source. When buying online, you can be sure that you will not get fake products and you are assured of after sales service. This is because the giant on-line retailers arrange for delivery to your house directly through the manufacturers of the product. Due to the high volume of business from the big online retailers, all manufacturers will make sure that any delivery on behalf of the big online retailers are of the best quality and that after sales service is provided on a priority basis.

If ever you have any problems, then you can go back to these online retailers and complain. All of these big online sellers have a reputation to keep and they always make sure that all complaints are promptly solved.

Advantage of buying AC, Fridge, Washing Machine, etc. online

Buying online fridges, washing machines, dishwashers and other major kitchen appliances is now the better option in India, just like it is in the USA and other advanced countries. There are several advantages of buying online. First of all, you get unbeatable bargain prices. Secondly, you get new and genuine products. Other benefits include no interest EMI payments, able to return the product for a full refund if not satisfied, etc.

Just to give you an example, below are some of the benefits Amazon India, the leading global online retailer, offered in India during their last sale. The same deals are not always available, but it is a good idea to check this link to the special offers page on India website.

Link to deals