Electricity Saving Tips For Homes And Offices

Ideal Air Conditioner temperature for electricity savings

By on March 6, 2014

Air Conditioner Temperature Buying an air conditioner once considered a sign of luxury, is now becoming quite common in India. Many urban homes are equipped with air conditioners in one or more rooms. But everyone who owns an air conditioner knows that it comes at the cost of increasing electricity bills. Although cooling does take a lot of electricity but taking effective steps can surely get it down. One of the main things that can help is maintaining the right temperature for the air conditioners.

How does an air conditioner work?

For most people, air conditioner just throws cool air at the temperature one sets it at. But does it really work that way? In fact air conditioner during cooling process, takes the indoor air, cools it  by passing it through evaporator coil and throws it back in the room. It is quite opposite to how our good old air coolers used to work. Air coolers used to take outside air, cool it with water and throw it in. But air conditioners just work on internal air.

How does the thermostat work?

If you set the thermostat at 18oC (64.5oF), does it mean that the air conditioner will cool the room faster than if set at 25o(77oF)? No. The thermostat just checks the temperature of the air inside the room and stops the compressor when the temperature reaches the desired level. This means that the compressor will work longer if the temperature is set to a lower level, i.e it will work more and use more electricity if temperature is set to 18oC (64.5oF) than if it is set to 25oC (77oF). This is because it will take less time for air to reach to 25oC (77oF) than 18oC (64.5oF) as the compressor is working with the same power or wattage.

What happens when the compressor stops?

The air conditioner just blows the fan when the compressor stops and thermostat reaches the desired temperature level. At this stage the electricity consumption is only for the fan which is running and not for the compressor. The compressor will start again when the thermostat detects that the temperature has increased again from the levels that are set. Compressor is the most electricity consuming component of an air conditioner.

What factors impacts electricity consumption of Air Conditioner?

There are 4 factors that influence the electricity load:

1) Indoor air temperature

2) Outdoor temperature

3) Thermal insulation of the room

4) Temperature setting of the air conditioner.

If the difference between temperature desired and indoor/outdoor temperature is huge, then the air conditioner will need lot more electricity to cool the indoor air to desired temperature as the compressor will run for longer duration. If the temperature is set at 18oC (64.5oF) and the outdoor temperature is 38oC (100oF) then the electricity required will be lot more than when thermostat temperature is 24oC (75oF) and outdoor temperature is 38oC (100oF). As per study by ACEEE (American Council of Energy Efficiency Economy), increase of each oC can save 3-5% of units consumed. This can considerably bring down the units consumed per month in the electricity bill.

What is the ideal temperature that should be set on thermostat?

Having said that, increase in temperature does not reduce the comfort level. In fact as per ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers), the ideal temperature for thermal comfort is between 23.5oC (74.3oF) and 25.5oC (78oF) in summers (depends on several factors as listed on wikipedia). Thus setting the temperature to 24oC (75.2oF) saves on electricity bill and provides good comfort. Using ceiling fans along with air conditioners can additionally help in increasing the thermostat temperature.Air Conditioner Temperature Infographic

Does “Quick Cool” option in Air Conditioners help?

Setting an air conditioner to quick cool sets it’s temperature to 18 or 16 oC (64.4oF or 60.8oF. This means that the compressor stops only when indoor temperature reaches this level. But while coming down from 35 or 40 oC (95oF or 104oF) it would have surely crossed 24oC (75.2oF) which is a comfortable temperature. So using “Quick Cool” option does not help because more electricity is used to get the temperature down to 18oC (64.5oF) whereas compressor would have stopped in between if the temperature was set to 24oC (75.2oF) thereby consuming less electricity.

How do old air conditioners without thermostat work? 

Old air conditioners without thermostat have high, medium and low cool options. As we learnt earlier that compressors of air conditioners work in binary mode (either they are on or off), an air conditioner without thermostat does not control air temperature. The high, medium and low options just changes the air conditioner fan speed. High means that air conditioner will throw more air and low means that the fan speed will be slow. The options do not change the temperature of the room, nor do they change the electricity consumption. 

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There Are 140 Comments

  1. Anumakonda Jagadeesh says:

    Excellent. Yes. Air conditioning consumes much of power mostly in Cities. According to one study in Mumbai out of 2700 MW Consumption Air conditioning share is 1000 MW !
    Dr.A.Jagadeesh Nellore(AP),India

  2. Karyn M. Bruce says:

    My husband keeps changing the thermostat all day long. When we go out, he sets the thermostat at a higher temperature (from 76 to 80). When we come home, it goes back down. When he go to sleep, it goes up. When I get too hot, I change it to make it cooler in the house. When he sees that, he sets it higher again. I believe that this constant change in A/C temperature affects the electric bill. Does it?

    • Abhishek Jain says:

      Hi Karyn,

      It will depend on the temperature outside. In winters if you keep temperature high, then heating will take a lot of electricity. In summers if you keep temperature low, then cooling will take a lot of electricity. Frequent change does not impact electricity bills, but the temperature difference between the room and the outside does.

  3. Usman says:

    Hi. I have two rooms.One is of 160square foot and the other 170 square foot. I am currently using a 1 ton A.c.I have installed a ventilating fan 250mm in the wall between the rooms which transfers cold air from one room to another. The thing is that the other room’s temperature becomes moderate, better than outside temperature but it does not cool.There is still a marked difference in temperature between the room containing the A.c and the one being controlled by the fan. I wanted to know if shifting to a 1.5 ton A.C would increase the cooling in the room controlled by the ventilating fan ?

    Kindly let me know.
    Thank you.

    • Abhishek Jain says:

      Hello Mr Usman,

      AC works very differently from an air cooler. Cooler takes air from outside, cools it and throws it inside. Whereas working of AC is very different. It does not take any air from outside, in fact it takes inside air, cools it and sends it back. The tonnage or cooling capacity of AC depends on the total amount of air inside a room. If the room is small you need smaller capacity, if room is big, you need bigger capacity. And that is also why it is always recommended to keep the doors and windows of the room closed while using AC because any amount of extra hot air from outside will increase the load on AC which will either result in extra electricity consumption and/or in inadequate cooling.

      The sizing is done not just based on size of the room but also on several other factors like: number of people, number of appliances in the room, etc as everything adds to heat in the room. It also depends on city where you live in as some cities are hot and some are cooler. Now 1 ton AC is small for 160 sq ft room even in cities like Mumbai where temperature is not high but humidity is high. And what you are trying to cool is 160+170=330 sq ft. And 1 ton AC will never ever cool 330 sq ft space. Even 1.5 ton AC would not work.

      The most ideal setup would be to have individual AC in each room for their individual size.

      • Usman says:

        Hey Abhishek,
        Thanks for your reply.
        I have installed 1.5 ton A.c . Its working very well . The thing is even if i keep the temperature at 28degrees,it gets very cold and i have to use a blanket.I want to know should I switch to a 1 ton A.c since I dont think a 1.5 ton A.C would be used to its full capacity. And whether a one ton A.c would be a cheaper option bill wise? I am using the 1.5 ton A.c at a higher temperature fluctuating between 26 to 30 degrees.
        The room dimensions are the same.160sq foot and a 170 square foot room linked together by a ventilating fan in between them.
        Thank you.


    hello Abhishek… appreciate your article.. I own 1 ton Godrej *** AC, by reading your article i keep temp @ 25 nowadays i wanted to know about the ideal mode and fan speed… the AC is installed in my bedroom say a standard family bedroom.the different modes are FEEL COOL DRY FAN & HEAT we often keep it in COOL MODE. the different fan speeds are AUTO HIGH MID LOW we often keep it in AUTO. are these ideal settings or should i change them. what you suggest ?

    • Abhishek Jain says:


      It truly depends on what keeps you comfortable. You should certainly derive the convenience that you need from your AC. 24-25 degrees is a good setting to keep. If you can keep it higher than that without being uncomfortable, nothing like it. Also looking at the number and kind of modes in your AC, it is better to keep it in cool mode. Dry mode would be good if you have high humidity. Also same for fan, if you are comfortable with low fan speed, then you can use that, however low fan speed will not circulate the air much, and if you are using a ceiling fan, then it would be good (as you can reduce AC fan speed as well as can increase AC temperature which can reduce your electricity bills).

  5. Buddhika says:

    can save energy by reduce air conditioner capacity for same heat load?

  6. prabu says:

    Thanks Abhishek for good article. Im living in chennai. My room is around 12X10sqft and located in first floor, direct sun light on roof and one side of wall, Im using 1ton LG split AC. Usually I used it during night time only, normally temperature will be around 34 – 38 deg. I have switched off swing mode in AC and have allowed to flow air in single direction directly to me. I always keep temp in 29 or 30 with energy saving mode enabled and fan speed is below normal. Is this good for power saving and AC? Whether I need to keep AC in swing mode, also I need to decrease temperature? What about fan speed? Please advice to save power and which is good practice for AC.

    Thanks in advance,

    • Abhishek Jain says:

      Hi Prabu,

      First thing that is important is your comfort. You should derive the comfort you need from the AC. 24-25 is good for body’s thermal comfort. If you are comfortable at 29-30 then that is certainly better for saving electricity. Certainly if the flow of air is directly towards you, then you will feel more comfortable. If you put it in swing mode then the air will not flow in your direction and you may not feel that comfortable. Even for fan speed: the electricity consumption is higher at higher speed and lower at lower speed. But your comfort is primary. Else AC will not solve its purpose. So I think whatever you are doing now is good enough. Additionally what you can do is get a reflective white paint applied on the roof top or get something like XPS (Extruded polystyrene) board put on ceiling. This will reduce the heat in your room. Try to put some sun film on windows that do not reduce light but reduce heat. You may also use thermal insulating wall paper. Do check our section on insulation: http://www.bijlibachao.com/save-electricity/insulation

  7. Khaled says:

    Thanks Abhishek for the nice write-up. My question is related to savings when the AC is in heating mode not cooling mode. Does the equation above work. If for example outside is 12C and temp is 24, now I set it to 20, the savings will be around 41%?

    • Abhishek Jain says:

      It should work in heating mode as well. However the savings will be (4/12)*100 or ((24-20)/(24-12))*100 so about 33%.

  8. ravi s says:

    In my office i am comforatble ac temp is 28 degree, but some told that if i put 28 degree ac may damage since comprosser will work minimum. it is correct. And sugest me 28 degrees ideal degree.

    • Abhishek Jain says:

      The compressor will have lower life if there is frequent switch on and switch off. And that will happen when you keep it too cold. So there should be no problem at 28. If you are comfortable with your AC temperature at 28, then it is the best. Below 24 should be avoided.

  9. MEENA says:

    Hi Abhishek

    i have bought LLOYD LS13A5LN AC 1 TONE 5 STAR , BUT its fan is not running at low fan speed .Please advice me there is problem in AC. it is just 2 day before installed. what you suggest , ? i should go for replacement ? tell me more thing to check, so i come to know its working properly or not.


    meena sharma

    • Abhishek Jain says:

      You should contact Llyod customer support and ask for inspection and replacement. Its fan should have options to run at high, medium and low speeds. It certainly looks like a problem. Does it not have option to run at low speed or it does but it is not changing to it?

  10. deep says:

    Is case if air conditioner is off but it’s switch remains in.so does the electricity bill comes

    • Abhishek Jain says:

      in some cases yes. Old ACs had 4-5 watts of standby power consumption. New ACs are much better (especially the split ACs). But yes it does consume electricity if switch is not off.

  11. Madan says:

    Hi Abhishek
    Nice article i have 0.75 Ton blue star ac, my room is 10×10 feet in second floor. My problem is whether i set any temperature, ac come to room temperatur then decreases temperature but never reach to my setting in remote . Is there anything wrong with ac or it is not sufficient for room. I am
    Iiving in new delhi.

    • Abhishek Jain says:

      You need 1 ton AC if your room does not get direct sunlight on walls or ceiling. If you do get sunlight then it would need 1.2 ton.

  12. Mohit says:

    Sir does split ac bring air from external environment ?
    If we keep room close will it suffocate?
    I have a voltas 1.25 ton ac.

  13. Sanjay Chandelia says:

    Hi, I have gone through most of your articles and they have been a deciding factor in purchase of my AC. Initially i had shortlisted Godrej 1.5T, 5 star AC but after reading your articles i went for Sharp AX-XP13PHT 1.1 Ton Invertor AC.

    My question is whether i will be able to recover my spendings. I live at Delhi, my room size is 9X12, height about 10Feet, middle floor, no direct sunlight, I run this at around 26-27 C.

    What would be the per hour unit consumption?

    Thanx and Regards.

    • Abhishek Jain says:

      As per my calculations, you need 1 ton AC for your room or 0.75 ton inverter AC. Even 1.1 ton inverter AC would work good. Electricity consumption should be about 0.6 to 0.7 units per hour max.

  14. arunkumar says:

    If we turn on Air conditioner compressor will (on) immediately or it will take some time (seconds or minutes). which one is correct? Please suggest.

  15. sanjay singhal says:

    Dear Sir,

    now a days, i am feeling less cooling from My window AC (1.5 T, Hitachi) in comparison to when it was new. How can i check the system is healthy.

    • Abhishek Jain says:

      How old is your AC? There is a concept of derating and with time the ACs derate and their cooling capacity decreases. But should not be a lot.

  16. tarun says:

    As u said ac will set 25 degree in less time than 18 degree its ok.and compressor stop, But as soon room temperature increases for say 26 degree or to 19 degree. Compressor starts it will take both same time to reduce 1 degree temp. So it vill consume same time same power.

    • Abhishek Jain says:

      It should consume same power and same time to reduce 1 degree temperature. However the room will get from 18 to 19 faster and it will be slow in going from 25 to 26. As the heat flow rate will be directly proportional to the difference between outside and inside temperature. So the compressor cycle will be more frequent at setting of 18 than at 25. So in a longer duration, power consumption will be more at 18 degrees.

  17. nida subhan says:

    Hii abhishek,
    Mai jan na chahti ho ki agar compressior per pani gir jae ya zyada garmi ho to hum pani daal sakte hain ac mai koi probblam to nahi hogi

    • Abhishek Jain says:

      problem तो नहीं होनी चहिये. infact अगर AC के आस पास काफी गर्मी है तो पानी ज़रूर डालना चाहिए , उससे AC अच्चा चलता है. वैसे भी बारिश के दिनों में AC पर पानी गिरता है.

  18. Suresh says:

    I brought Samsung split AC 1 ton 4 years before since now i never seen my AC temp reduced less than 26 after running continue 9 to 10 hrs, most of the time it will touch the Temp max 28 after running 4-5 hrs.
    1. My room temp will be 34 -35
    2. My ODU is kept directly face to sunlight
    3. The ODU and IN-DU is just attached by the same wall, but inside and outside
    4. What mode has to be kept in summer season

    What should i do get a cooling air?


    • Abhishek Jain says:

      Which city are you located in and what is the size of your room? From your response it seems one of the wall is directly facing the sun, does the roof also exposed to sun or do you have more floors above the room?

      • Suresh says:

        Abhishek, First thanks for your reply. I am from chennai, we stay in first floor there is no building above and side. My room window and door is fully enclosed with glass not wooden door so the sunlight directly fall to my room. size of my bedroom is small coarsely i can say 12×15. considering my room size i brought 1ton.

  19. tapan says:

    Sir pl suggest. i bought a new 1.5t window ac and after installation set temp to 23 c.
    from the night of the installation if find
    1) compressor takes about 5 minutes to start after switching on the ac till then the lcd display shows “UP” (installation person said it happens for the first day only)
    2) in the middle of the night again the compressor was off and only fan running for a long time . the lcd display again shows “UP”. and room was not cool.
    Is this the first day blues or a defective unit pl advise

    • Abhishek Jain says:

      Hello Mr Tapan,

      It sounds like a defective piece, as the compressor should not go off at Night. Can you check if it is running in the right “mode”? Make sure it is in cool mode.

  20. meenal says:

    I have 1.5 ton ac how much bill will come if i set it at 13 degree celsius

  21. raza says:

    Hi, I wanted to know how much average time a room ac takes to achieve a set temperature from the time it is switched on, assuming set temperature was 24 degrees.

    • Abhishek Jain says:

      Depends on room size and in general on the heat in the room and heat outside. However if you have sized your AC properly, it should not take more than 15-20 mins.

  22. Rishabh says:

    I am looking for an air conditioner which is power efficient as well as should have a good performance at the times when there is high outdoor temperatures..
    I concluded to go for an inverter ac of 1ton..

    The thing which is confusing me is operating temperature of compressor. In my city temperature hits 48 sometimes 49 in peak summer.. But all good brands (general, daikin, mitsubishi, etc) gives operating temperature till 46.. I have seen only hitachi claiming it is designed to work on 52…

    I this condition, how significant is this criteria while choosing the right one or is hitachi the only option left for me?

    • Abhishek Jain says:

      Hi Rishabh,

      Typically if the temperature is very high around the outdoor unit and there is direct sunlight on it, the efficiency of condenser goes down. To a certain extent it will try to work by consuming more electricity, but if the temperature goes really high, the compressor stops working and the air does not get cooled. However you can avoid that situation by making sure that the ODU does not face the sun directly and is in a place that has a good shade or is surrounded by plants that keep the temperature around the ODU cooler. So if you go for a model which has operating temperature of 46, you will have to take care in placing the ODU in a place that is cooler as compared to outside and does not get any direct sunlight.

  23. saialuka says:

    we have 1.5 ton 3 star a.c during night time temperature changes automatically from 22c to 24,25,26c gradually is thi normal in energy saving mode.

    • Abhishek Jain says:

      Well if temperature increases, it will certainly save energy. Unless it is causing any discomfort, it should be good. Every brand has different kind of energy saving modes. In some ACs, the AC actually switches of completely for some time in energy saving mode and restarts automatically after some time.

  24. sandy says:

    Hi sir
    my name is sandy my room is 8 x 10 i have window ac 0.75 ton voltas 2 star my question is how much to consume Tha electricity unit for 1 hour plz reply .thanks

  25. kiran kumar says:

    sir my name is kiran kumar from jammu my room is 12 x 12 i have window ac 1.5 ton my question is 1. under what condition we will change the speed of fan low to high and high to low question 2 it is possible to use comprassior only and fan will be off if yes under which condition. qurstion 3 if outside temp is 45 than what is the room temp to be set without fan.

    • Abhishek Jain says:


      Fan is absolutely necessary in an AC. You can alter the fan speed from low to high but you cannot run an AC without it. When you want higher air flow in your room/ faster cooling then you need higher fan speed. Once the room is cool enough, you can switch to lower fan speed. Ideal temperature is about 25 degrees.

      • kiran kumar says:

        thanks sir i have few more questions. 1. is there any time line for switch off of ac so that it can take rest i am asking this question because my ac is continuosaly running more than one day . question 2 i our remote two option shown for cool which one is better a) first showing sun b) second showing 6 corner. i confuse which one is better. most of time i change 1 to 2 and 2 to 1 but no difference found is there any difference

        • Abhishek Jain says:


          There is no guideline specific for switching off an AC. But it will be better if you switch it off and open up your room for some external air for better air quality in your room. Else the air inside will become stale and it will not be good for your health. Also every brand and model have different options, so I am not sure about the two options you are talking about. Which brand and model do you have?

        • amjad says:

          What is the ideal position for remote setting for Electricity saving. there are three options 1- Auto 2-Cool 3-Dry. I have Panasonic Inverter, Econavi Split AC.

  26. Shahid says:

    I have an lloyd 1.5 ton 3 star split ac and room size is 10×12 feet on first and top floor, kindly advise how I can save electricity as it seems that it is using 2+ unit/ hour

    • Abhishek Jain says:

      Hi Shahid,

      There are several ideas in our insulation section that you can try: http://www.bijlibachao.com/save-electricity/insulation , especially the reflective white paint on the roof top and XPS (extruded polystyrene) insulation boards. Also you should try to keep the AC on as high temperature as comfortable. 25 should be ideal. Once you have done the insulation, try using ceiling fan along with the AC which will help you increase the temperature settings on the AC. Also make sure that you get regular maintenance done for your AC.

  27. vijay says:

    Im using lg window ac,1.5 t, 3star
    Im in sirsa,haryana
    The temp is above 40
    If i use ac whole night what will be my avrg electric bill
    Please help

  28. S.K.Sharma says:

    What does 1 ton or 1.5 ton actually mean ?

    • Abhishek Jain says:

      Ton represents speed at which AC can remove heat. You can read more at: http://www.bijlibachao.com/air-conditioners/air-conditioner-selection-understand-tonnage-eer-cop-and-star-rating.html

  29. azhar says:

    if i keep my AC at 26oC than electricity will consume more or at 25oC?

  30. Inderjeet singh says:

    good morning sir the Air conditioner of 1.5 ton how much unit get if we set temp 25 digrees auto indoor while outdoor temp is 45 digrees ( room is 10 feet x 12 feet ) looking forword for your risponse thanks

  31. VK Singh says:

    I have bought a 1.5 ton used AC from RK Refrigeration in New Delhi. It is installed in a room that is 15′ X 10′ X 8 ‘. The room is in a single storey building with a concrete roof. The outdoor unit is installed on the roof. The cooling appears to be less, when compared to a window AC in the neigbouring room of the same size. What is the ideal temperature at the vent of the AC?. How does one go about measuring it? Where can I buy a temperature gauge ?

    • Abhishek Jain says:

      Hello Mr Singh,

      1.5 ton is a good enough size for your room. It should work fine. May be that you AC’s outdoor unit is not working efficiently because it is getting direct sunlight on it’s outdoor unit. Efficiency is less when the outdoor unit is in a hot environment. Secondly the temperature near the vent should be the temperature you have set on the thermostat. And you can measure it using a room thermometer. You can easily get one in the market.

  32. Sudharsan says:


    I want to purchase Ac
    1. Split AC or floor standing AC
    2. Direct Sun Light on Roof & West side, so wall or too heat.
    3. What tonnes 1 or 1.5.
    4. i want to save power.

    please suggest me sir.


    • Abhishek Jain says:

      Which city is this for? What is the size of the room? How much is your usage in hrs/day and months/year?

  33. Titus says:

    I have voltas 1.5 tone split AC. The thermostat does not switch off the compressor when the desired room temperature is attained. This happens for the last one week.

    • Abhishek Jain says:

      What is the size of your room? Which city are you in? Does any of your walls/ceiling get direct sunlight? If AC is undersized, the compressor may not switch off. But undersized AC may not cool to the desired temperature as well. How are you measuring the room temperature?

  34. Jay says:

    its mentioned that changing temperature from 20 to 25 will give 20% savings. What is the time duration for that means in how much time it will provide 20% savings? Kindly help.

    • Abhishek Jain says:

      Hi Jay,

      Firstly the savings will also depend on outdoor temperature. Also as mentioned in the picture, it is an approximation. The AC compressor will switch off earlier (from the time you start the AC) if you keep thermostat at 25. Also the in between cycles will be shorter. So even in an hours use, you can save electricity.

  35. nitin says:

    Hi Abhi… I want to ask u that my room dimensios are 12*9*10 at ground floor above there are 2 floors more.. No direct sunlight at all ..I m in delhi…. What should be the size of AC?? Thanx in advance

    • Abhishek Jain says:

      1 ton AC would be good for you.

      • nitin says:

        Hi… But I bought a 1.5ton 3star voltas 183dya Ac .. My daily usage is around 5 hours.. Is it worthy.. And one more thing..
        With in one week my outdoor unit leaked gas.. So after talking to dealer I replaced it..but this model wasn’t available at him so he give me outdoor unit of another model 183pya.. Whose marked power is 1616W where as previous model power was 1532w…. So will the replaced unit created problem as indoor unit is of another model and outdoor unit is of another model… Whereas EER fir both model was same 3.15..

        • Abhishek Jain says:

          Hi Nitin,

          DYA is the delux version and PYA is premium version. PYA has higher cooling capacity (5150 as compared to 4850), which means it will cool faster and more. But will it be really beneficial is something that one can determine only by knowing the need of your room. Which city are you from? What is the size of your room? Does any wall/ceiling get direct sunlight? Typically over sized AC over cool and thus result in extra electricity consumption. So if AC is over sized and you keep the AC at 25, it may cool up to 22 or 20 degrees as it has higher cooling capacity. It should not cause problem in working, it may just consume extra electricity.

  36. abir banerjee says:

    hello abhishek, i purchased daikin 1 ton inverter ac ftke35gv1 couple of days ago. my house is on top floor size 100 sq/ft, wall height 10 ft . the aircon seems works ok but not good enough. i switch on the aircon in afternoon when the outside temp is 40° c i set the temp 20° c and after 2 hour its only cool down to 25° c and the next 30 mins it’s barely cool down to 24° c but never 20° c. bt at night it’s catch the set temp.
    my house is well sealed, i don’t know is it normal the way my ac works or not?

    • Abhishek Jain says:

      Hi Abir,

      Which city are you in? Although 1 ton inverter AC for 100 sq/ft sound quite reasonable. How are you measuring the temperature in the room? Where is the thermometer kept in the room? If you keep the AC at 20 and it does not cool it down to that temperature then it does not sound right. However let me take this image as reference to explain you how inverter AC works:

      Inverter AC

      non inverter ACs are fixed speed ACs, where as inverter ACs are variable speed ACs. Non inverter ACs have compressors that go “On” and “Off”. Whereas inverter ACs have compressors that are “On” all the time. As non inverter ACs are sized for peak summer load, they are over sized all the other times (in fact most of the time people oversize even for peak summer season). The drawback of the same is that the AC “Over cools” most of the time. So if you set AC at temperature of 25, it will cool it down to 23 or 22. Now one would question: then what is the use of thermostat? Well the thermostat (in a non inverter AC) switches off the compressor when the outside temperature has reached 25. But a lot has happened before that. In an AC, refrigerant moves from liquid to gas (by taking heat from the room) and then back from gas to liquid as the compressor compresses it. But if the refrigerant is more and heat in the room is less (which happens in over sized AC), it does not get enough heat from the room to convert from liquid to gas and it keeps moving as liquid. Now when the thermostat detects temperature and switches off the compressor, the refrigerant still remains in liquid state and thus has capacity to take heat from room to convert to gas. And so it takes more heat from the room and cools the room below the set temperature.

      In comparison, the inverter tech AC changes the flow rate of refrigerant based on the heat of the room. When heat is less, the flow rate is less, when heat is more, the flow rate is more. And it does not switch off the compressor ever. It just makes sure that if temperature setting is 25, it is maintained at that level.

      So the difference is: non inverter AC would over cool as shown in the picture. Whereas inverter AC will cool optimum. And thus you may feel that inverter AC does not cool or is slow.

      Hope this helps.

      • Abir Banerjee says:

        thanks abhishek for your quick and helpful reply, i got it now. i am from kolkata i scale the temp with a thermostat 15 ft away from the ac vent. and one more question my unit is installed 9 ft above the floor, and the distance between ceiling and the unit is 6 inch is that ok ?

        • Abhishek Jain says:

          Hi Abir,

          15 ft is a little far away from the AC. Mostly ACs have a reach of 7-8 ft unless you put on the fan so that the cold air circulates. And the thermostat measures the temperature of air near the vent. 9ft above the floor and 6 inch space is fine for the AC.

  37. Manish Gaur says:

    Hello Abhishek, Indeed this discussion is very informative and I got most of the answers to my curiosity.

    I have recently purchased a 1.5 ton split Ac with 2 star rating. can you please give me an idea about how many units of electricity it will consume each day by assuming the run time of around 8 hours and the temperature setting at 20-22 degrees. On the cover they have written around 1852 watts for power consumption.

    Looking forward to your quick and informative reply.


    • Abhishek Jain says:

      Hello Mr Manish,

      Your AC will consume approximately 1.852 * 0.7 = 1.3 units in an hour when you keep the internal temperature to 22 and external temperature is about 33-34 degrees (considering that the AC is rightly sized). If the outside temperature is higher or AC is undersized, it will consume more up to 1.9-2 units an hour. Or if you keep it at 20, again it will consume more.

  38. Inderjeet Maurya says:

    If i hang black plastic sheet on the wall directly getting exposed to Sun light, will it not help reducing temperature of wall of my room and hence help my AC work more efficiently?

    • Abhishek Jain says:


      It will be better if you hang white plastic sheet instead of black. Black absorbs heat, whereas white reflects heat.

  39. Balaji says:

    Is it better to keep the fan in auto mode or select manually at preferred level namely 1, 2 or 3 while in cooling mode from an energy efficiency aspect and comfort aspect. I have 1 ton ac for 150 sq ft room. Thanks.

  40. Amogh says:

    i have carrier kurve split 1 ton ac.. i have to keep it at 17 degree celsius then only it cools the room. at 24 degree celsius i start feeling hot.. What would be the problem with my ac?
    Any suggestions? I live in Mumbai

  41. Kaushik says:


    I have just purchased a 1.5 ton 3 star LG split ac which gives pretty good cooling at 26 deg. I live in Chennai and its peak summer time here. My room is about 130 sq.ft. My query – is it okay if i keep switching the AC on and off for 3 or 4 times a day depending on my usage [by switching off i mean i switch it off entirely including the stabilizer]. Or should i just switch off the machine alone and let the stabilizer run the whole day.

    And also, being in Chennai during summer, it is necessary for us to us the AC for the whole night as well as during the noon time for about 4 to 5 hrs. So we ll be using it for about 12 to 14 hours a day atleast for another 2 months. Is that okay.

    Any tips on energy saving.


    • Abhishek Jain says:

      It is perfectly fine to switch off the AC along with stabilizer. In fact if you are not using the AC, there is no point in keeping the stabilizer on.

      There are several things that you can do to save electricity:

      1) Make sure that the doors/windows are closed when the AC is on.
      2) Do not stuff the room with things as every thing will need cooling and will increase electricity consumption.
      3) Have as less appliances switched on in the room as possible when you use AC.
      4) You can try insulating walls/ceiling if they receive direct sunlight during the day. Use thick curtains or insulate windows by using heat blocking sheets on window.
      5) Use ceiling fans with AC which can let you increase temperature on your air conditioner without reducing comforts and thus help saving electricity.

      You can find a lot of details on our

      AC section: http://www.bijlibachao.com/save-electricity/air-conditioners
      Insulation section: http://www.bijlibachao.com/save-electricity/insulation

  42. Nitish says:

    Hi ,

    I bought a LG 1ton inverter . Its working fine . But electricity usage is almost 12 units in days . I use it for 10 hours everyday . Is it normal ? Thermostat is set usually at 24.

    One more doubt is the coolant inside outdoor unit ? Bcz service people didnt fill any and checked any pressures .

    • Abhishek Jain says:

      Which city do you live in and what is the size of your room? 12 units in 10 hours for a ton inverter AC is on a higher side. It cannot happen unless your AC is undersized (which mean compressor is running at top speed most of the time).

      The refrigerant moves between indoor and outdoor unit. But is filled in outdoor unit during maintenance.

  43. Raja says:

    Voltas vertis platina 1.5 WAC is showing E2 error message. Compressor runs for some time then only fan. What could be wrong?

  44. saikat chakraborty says:

    Hi abhishek, I am cnfusedd about sharp eer rating of 4.41 in AHXP18PMT because its rated cooling capacity is 5270 watt and power input is 1440 w.So please calculare for me the eer .

    • Abhishek Jain says:

      Inverter ACs have a range of EER as they have varying cooling capacity and corresponding varying power consumption. Typically EER is high at lowest cooling capacity and lowest at highest cooling capacity. 4.41 is the highest cooling capacity of the model. The nominal EER is 3.66 which is 5270/1440.

  45. chanshuk says:

    Hi Abhishek

    Thank you for reply.

    I stay at Ahmedabad, and cost of electricity per unit is almost Rs. 6.5 / Rs. 7. Expected temperature to run is around 25/26. The room is on the upper floor (first floor) and catches direct sun light in the morning.

    I have found the EER of Daikin 1.5 Ton Inverter FTKP50PRV16 as 3.46. I am trying to find the EER of the Mitsubishi model, to calculate the savings as you have explained.

    Checked with the dealer and the model name is Mitsubishi SRK 18 CL 1.5 Ton 3 Star. Now, I can find this on few sites but none of the popular one. And also, still not on the Mitsubishi site. Please let me know your thoughts on the Mitsubishi SRK 18 CL if compared to Daikin inverter model and which one of the two would be best in terms of savings and price.

    Thanks again.

  46. chanshuk says:

    Hi Abhishek,

    A nice article and helpful replies in comments.

    I have a room of around 160 sq feet. I expect the AC / Inverter to run for around 6 hours a day for 4 months / year. I am confused between whether to buy a 1.5 Ton 3 star ac (Mitsubishi rsk18cl) or the 1.5 Ton inverter (Daikin ftkp50prv model), the price difference between the two is 10,000. I am more towards inverter but would it be able to save me enough if I am spending 10,000 more in comparison to 3 star AC?

    Also, I don’t find much information for Mitsubishi rsk18cl model (Dealer suggests this model) – not even on the Mitsubishi site : , whether this is an old model or a latest one can you throw a little light on this too?

    Thanks in advance!!

    • Abhishek Jain says:


      Which city do you stay at? Typically we recommend people to go for BEE 3 star rated AC is usage is less than 1000 hrs and price of electricity is Rs 5 per unit (if price is more, the hours come down), for BEE 5 star when usage is between 1000-1500 and inverter tech if usage is 1500 and beyond (at Rs 5 a unit). However a very important thing to consider is EER.

      Inverter tech is 15-20% more efficient at the same EER of BEE 5 star. So if two ACs both at nominal EER of 3.5 one BEE 5 star and one Inverter Tech, the inverter tech will give 15-20% savings. However if the nominal EER of Inverter tech is 3.2, then that means that at 1.5 ton Inverter tech is 9% less efficient. So you will have to reduce 9% savings from that.

      %savings at 2 different EERs can be obtained as ( (1/EER1)-(1/EER2) ) *100 / (1/EER1) so 1/3.2 = 0.32 and 1/3.5 = 0.29 so efficiency = (0.31-0.29)/0.31 = 0.09 or 9%.

      Now a typical BEE 3 star rated AC at temperature setting of 22 would consume 1.3 units in an hour (or 0.7 * wattage / 1000). So based on your usage of 720 hrs, your unit consumption would be about 936 units a year.

      By the way even I could not find the model. You need to ask for more details from the dealer.

      • chanshuk says:

        Hi Abhishek

        Thank you for reply.

        I stay at Ahmedabad, and cost of electricity per unit is almost Rs. 6.5 / Rs. 7. Expected temperature to run is around 25/26. The room is on the upper floor (first floor) and catches direct sun light in the morning.

        I have found the EER of Daikin 1.5 Ton Inverter FTKP50PRV16 as 3.46. I am trying to find the EER of the Mitsubishi model, to calculate the savings as you have explained.

        Checked with the dealer and the model name is Mitsubishi SRK 18 CL 1.5 Ton 3 Star. Now, I can find this on few sites but none of the popular one. And also, still not on the Mitsubishi site. Please let me know your thoughts on the Mitsubishi SRK 18 CL if compared to Daikin inverter model and which one of the two would be best in terms of savings and price.

        Thanks again.

        • Abhishek Jain says:

          You need 1.8 ton cooling for your room. If you go inverter tech, a 1.5 ton inverter AC would work for you. If your usage is more than 800-900 hrs a year, go for BEE 5 star rated AC. If it is more than 1300-1400 hrs a year, go for inverter tech.

          Mitsubishi Inverter tech model of 1.5 ton (MSY-GE18VA) has EER of 3.36.

          Hitachi Ace Inverter
          Samsung AR18HV5DAWK
          Daikin FTKM50PRV16 all 3 have EER of 3.8

          Hitachi iClean Inverter EER of 3.73
          LG BS-Q186C8R6 EER of 3.67
          Sharp 1.5 ton models have EER of 3.66

          The Mitsubishi model you mentioned has EER of 2.8. Inverter tech of same EER would save 15-20% extra because of its variable tonnage feature.

  47. Sonal says:

    Fantastic article. Exactly what I was looking for.

  48. Arunabh says:


    I have a window AC of BEE 5 star level. My room is of 14 x 11 ft. No direct sunlight comes to my room. What will be the ideal temperature at night when sleeping.


  49. Suditie says:

    Best air conditioner for a medium sized room. ….for small flats in split options

    • Abhishek Jain says:


      There are several factors that one need to consider while buying AC:

      1) Tonnage of AC: Depends on several factors, but primarily on size of room, city where you live in, window sizes, people in the room. Oversized AC consumes more electricity, and undersized does not cool properly.

      2) Star Rating: Choice of BEE 5 star/inverter tech or a lower rating depends on your usage of AC. If your usage is more than 1000 hrs (with traiff more than Rs 5), it is better to go for higher efficiency models. Benefit of inverter tech is that it is a variable tonnage AC and as the tonnage requirement is different every month and every day, this AC auto adjusts to the needs and thus saves electricity.

      3) Brand: Some brands offer better reliability/technology and some have better service network. One has to factor in both. Once you have decided on star rating, the most efficient models from good brands can be selected.

      If you provide us with more details as in which city do you live in, size of your room, which floor is it on, is there any floor above it, are the walls exposed to sun, usage in hours per day and months per year, and approximate budget, then we can recommend you something.

      Hope this helps.


  50. Pradeep says:

    just want to know that all major brands like Daikin and O general is having a operational temperature of 46 Degree cel in there inverter ac, so what will happen if the ambient temperature goes beyong 46Deg/C. Is the ac shut of or still remain working.

    • Abhishek Jain says:

      Hello Mr Pradeep,

      Can you please share the link where you have seen this? All I can say is that if temperature is high and the cooling capacity of any AC is low (as per the heat load), it may not cool effectively, but I don’t think any AC shuts off because of this. I have seen people use small 1 ton AC for a large 200 sq ft room. They do not cool properly but they do not shut off.

      Hope this helps.


  51. Gaurav Dighe says:

    Dear Abhishek,

    Thanks for the article, it provides simple explanation to Air Conditioning basics.

    Once the set temperature is achieved the compressor stops, right, then what is the differential temperature after which the compressor starts again. My guess (2 to 3 deg C).

  52. Nomad Travel says:

    ASHRAE standards are notably not reliable, since they are working to increase the sales of the industry. 24°C is way too low, and in particular if outside there are 35°C 40°C it’s an incredible thermal shock for the body

  53. Rameez says:

    Nowadays these AC’s have an option of “AUTO” mode cooling. Does this help in lowering the electricity bill ?

    • Abhishek Jain says:

      Hi Rameez,

      “Auto” mode is better, but the most important thing is the thermostat setting. If it is too low, then it will not help. It needs to be set right (about 24-25 degrees or may be higher) to get right amount of savings.


  54. Abcd says:

    This is a big help :)

  55. Ramshiva says:

    Hi abhisekh,

    Very good informative article yu have provided but i would like to know i am using 1.5 ton voltas a.c, on the prodcut they have written 1870 watts per hour consumption what it means at what temperature will it consume this wattage per hour.is it 18 or 24 degrees. pls help.

  56. Srinivas Rao says:

    I have a question if we on and off the ac does have any impact on power consumption.

    • Abhishek Jain says:

      It depends on how frequently you do it. If there is considerable time difference (say about a few mins or so), then power consumption will be less.

  57. Niren says:

    Thats really Informative….Thanks for nicely written aricle

  58. Sandeep says:

    Hi Abhishekh,

    Nice Article there. I have a question. Nowadays these AC’s have an option of “AUTO” mode cooling. Does this help in lowering the electricity bill ?

  59. kalpan says:

    i want to knowhow much energy consumption reduce by using sleep mode in ac per month?

  60. Sachin. says:

    Hi Abhishek
    Your site is excellent, I have actually got answers to many of questions by reading different articles posted.

    • Abhishek Jain says:

      Thanks Sachin. I am glad that you found it useful. You can sign up for our monthly newsletter with which we provide latest updates on the site and also provide seasonal tips.


  61. yagnesh says:

    I want know about capacity of Air conditioners i.e, 1 ton or 1.5 ton will effect the power bill, and which one gives fasstest cooling

    • Abhishek Jain says:

      Hello Yagnesh,

      Choice of 1 ton or 1.5 ton depends on size of the room, number of people in the room, number of things kept in the room and the number of sun facing walls. A 1.5 ton AC may not be effective in removing humidity in a small room and a 1 ton AC may not be effective in cooling a big room. Lot depends on size of the room. Although we are in process of collating information on sizing of air conditioners, if you can let us know the size of your room, we can suggest you the right size.


  62. Ramesh Shivnani says:

    pl.through some light on efficient motors (for fans,compressor)efficiency of condensers, filter, regular service,its part in saving power if any?

    • Abhishek Jain says:

      Hello Mr Sivnani,

      We have a different article on the same topic: http://www.bijlibachao.in/Air-Conditioners/air-conditioner-maintenance-and-operation-tips-for-electricity-savings.html.


  63. LittleCrow says:

    This Information was very helpful.Thank you

  64. Priyadarshan says:

    First of all, I must say that your site is really excellent. Very useful as well.

    I would like to know, what if the temperature is set to 27 degrees instead of 25 degrees? Will it save more electricity?

    Please let me know

    • Abhishek Jain says:

      Thanks for the good words Mr Priyadarshan. As for your question, you would surely save more electricity if you keep the temperature to 27 degrees. The air conditioner works to bring down the temperature of the room to the temperature set in the air conditioner. If the difference between room temperature and air conditioner is less, then the air conditioner will have to work less and thus it will consume lesser electricity. So certainly electricity consumption will be less at 27 degrees setting.

  65. rajiv mehta says:

    my dear friend, it is not the ‘ condenser ‘ which shuts off when the desired room temperature is achieved but it is the
    ‘ compressor ‘. plz make necessary correction in the article.

    • Abhishek Jain says:

      Mr Mehta, Thanks for your observations. The article has been corrected.

      • ASMA says:

        plz help me ,i want to know that .the thermostat is in every AC’s??? i have Sabro Split Ac but its compressor is not turning off when room temperature is maintained.Where is problem????

        • Abhishek Jain says:

          Hi Asma,

          All ACs have thermostat. So either your AC is smaller for your room or certainly there can be a technical problem.