I wanted to find out the right tonnage to buy AC for my office. I did some research online to find out ideal AC tonnage as per room size.
To my surprise, most of the numbers did not match up with my experience.
- Some ask to divide the volume of the room by 1000 to get the tonnage.
- While some are of the view that multiplying the area with 25 will give you correct energy usage.
To my surprise, I found out that both the information are wrong.
Many AC salesmen in India will give you wrong information so that you end up buying larger AC than you need. They will tell you to divide the volume of the room by 1000 to get tonnage because it will always give you higher tonnage.
On the other hand, if you multiply the area by 25 to find out energy usage, this calculation will not be applicable in Indian context.
Don’t worry, I spoke with experts to find out the correct room size for 2 to 1 ton AC in India.
First of all, let’s understand the basic guide to choose the right ton AC as per room size.
Table of Contents
The Right (& Wrong) Ideal AC Tonnage as Per Room Size
While researching for the relationship between tonnage and room size, I found numbers varying wildly. Here is the reason for this confusion.
Certain countries such as the US uses BTU instead of ton to denote the AC capacity. Relationship between BTU and tonnage is this:
1 Ton AC consumes 12000 BTUs/hour
Hence, an AC with 12,000 BTU rating is similar to an AC with 1 ton rating in India.
However, if you see the EPA guidelines (US), relationship between BTU and room size is clearly indicated.
If I follow this guideline from the US government, 1 ton AC should suffice for a room of 550 square feet. It is easy to figure out that this is NOT CORRECT for India.
I spoke with few experts in the AC industry to find out the right room size as per tonnage in Indian context. This is what they have to say.
- US numbers are around 3 times of that of India
- 1 ton AC is ideal for a room of 12000 cubic feet volume in India
This is sufficient to get at these numbers.
However, there are few more factors that should be kept in mind to find out the ideal tonnage for your room.
- If your room gets direct sunlight then increase the tonnage by 10%. Similarly, decrease the tonnage by 10% if there is no direct sunlight in your room. Bungalows, a cottage type houses with open terrace are possible candidates.
- Each person adds around 0.1 ton. It means that if on an average 4 people will occupy the room, increase the ideal tonnage by 0.4 tons.
- If the area includes the kitchen (such as studio apartments), the add 0.2 tons.
2 Ton to 1 Ton AC Room Size
Ideal room height in the US (as per EPA) and India is usually taken as 8 feet. This now gives me the best way to calculate the right room area to find out the correct tonnage.
|Room Size||Room Volume||AC Tonnage||BTU|
|100 sq. ft.||800 cu. ft.||0.7 ton||9,000 BTU|
|150 sq. ft.||1,200 cu. ft.||1 ton||12,000 BTU|
|230 sq. ft.||1,800 cu. ft.||1.5 ton||18,000 BTU|
|320 sq. ft.||2,560 cu. ft.||2 ton||24,000 BTU|
We can clearly see that for a room of up to 150 square feet area, you can use a 1 ton AC.
All you have to remember is this: You need 0.0066 tons of AC per square feet.
In short, if you want to cool an area of 150 square feet, then, this is the formula for AC capacity calculation:
AC Capacity = 150 sq ft * 0.0066 tons/sq ft = 1 Ton
All you need to remember is that you need 1 ton AC for 150 square feet room. You can also use this formula to calculate the tonnage.
AC Capacity = (Area in square feet) * 0.0066 tons/sq ft + number of people*0.1 + 0.2 (If studio apartment)
Other Factors That Should Be Considered
Extremely Hot Climate
If you stay in an area with extremely hot climate, then add an extra 20% to the final tonnage calculation.
Agra (Uttar Pradesh), Chittorgarh (Rajasthan), Churu (Rajasthan), Jhansi (Uttar Pradesh), Ganganagar (Rajasthan), Pilani (Rajasthan), Phalodi (Rajasthan), Bundi (Rajasthan), Gwalior (Madhya Pradesh), Hissar (Haryana) are top hottest cities in India.
Type of Furniture
Most of the area in the room is occupied by furniture. Hence, its type plays a role in tonnage calculation.
Metal and wooden furniture have different heat absorptions. Meta furniture absorbs more heat, which means that if you have more metal furniture, then add 0.1 ton to the actual tonnage. If you have wooden furniture only, then no need to add anything.
Type of Roof
If you have concrete roof, then you don’t have to worry. However, if you have a false ceiling/asbestos ceiling, then you will have to add 0.1 ton to the final tonnage.
Given all other things constant, you can follow this as a rule of thumb:
- For Room size less than 100 sq ft go for 0.75/0.8 Ton AC.
- For Room size between 100-150 sq ft go for 1 Ton AC.
- For Room size between 150-230 sq ft go for 1.25 or 1.5 Ton AC.
- For Room size between 230-320 sq ft go for 2 Ton AC.