Proper sizing is very important for efficient air conditioning. A bigger unit is not necessarily better, because a unit that is too large will not cool an area uniformly. A small unit running for an extended period operates more efficiently and is more effective at dehumidifying than a large unit whose cycles switch on and off too frequently.

The thumb Rule for Tonnage

 The Bureau of Energy Efficiency (BEE) gives  the basic thumb rule for selecting appropriate sized AC for our needs.

0.75 Ton (AC capacity) – 75 to 100 sft (Room size)

1 Ton – 100 to 150 sft

1.5 Ton – 150 to 225 sft

2 Ton – 225 to 325 sft

3 Ton – 325 to 450 sft

3.5 Ton – 450 to 575 sft

The Star rating effect

Now couple that thumb rule with the ‘Star rating’, you almost have the perfect energy saving AC for your room. The Star ratings start from 1 to 5, with 5 being the most energy efficient. Ask any sales person in any AC showroom regarding 5 stars rated AC’s, they will all say the same thing ‘go for the 5 star, if you use your AC for at least 10 hours a day’. While that is almost a correct statement, lets get more practical and see how mush you can save ‘per year’, when you use a 1 star, 3 star and a 5 star AC under some fixed conditions.

More Rated ,More savings….

For this purpose, I’m going to consider the most common household choice of AC (Split, that is) which is a 1.5 TON AC that is used for a 150 – 225 sft sized room and lets just say that you use the AC for 12 hours a day for 150 days in a year in a hot and humid city like Hyderabad.

For a 1 Star AC, the annual Electricity bill you will incur is about Rs.16341 (Rs.1361/month).

For a 3 stars AC, the annual Electricity bill could be Rs.14002 (Rs.1166/month).

For a 5 stars AC, the annual Electricity bill could be Rs.12249 (Rs.1020/month).

For most of the household, those bills per month could be quite burdensome, but the thing to look here is the difference in savings between 1, 3 and 5 star rated AC’s.

The savings details for a 1 Ton AC .

1 TON AC (for 12 hours a day and 150 days a year)

1 star rated AC can bill up to Rs.10894 per year (Rs.907/month)

3 stars rated AC can bill to Rs.9335 per year (Rs.777/month)

5 stars rated AC can bill up to Rs.8166 per year (Rs.680/month)