BTU stands for British Thermal Units – it is a measurement of heat which is defined as the heat that is necessary to increase the temperature of one pound of water by one degree fahrenheit.
Now this seems really technical, but what you really need to know is just that this is relevant when looking to buy air conditioners because it is the standard used to measure how many units of heat an air conditioner can remove. So you would use it to ensure you're buying an air conditioning system that can remove sufficient heat from your space – otherwise you will be sitting in a hot room even though the aircon is on!
While the definition of BTU is complex, calculating the amount of BTU that you need for your space is actually surprisingly simple. All you have to do is to multiply the length of your room in feet by the width of your room in feet, and then multiply that by 25. That will give you the BTU needed to properly cool your room. All it takes is a simple multiplication!
Here is a really easy example: Most HDB rooms are around 5 meters by 3 meters. First we convert meters to feet, so that gives us around 16 feet by 10 feet (to convert meters to feet, you can multiply by 3.3). Multiplying those two numbers together, we get 160. Then we take that and multiply again by 25 as mentioned above. That gives us 4000 BTU using the formula defined above. So to cool a standard HDB room would take an air conditioner with 4000 BTU of cooling power. It is that straightforward!
If you don’t pick the right BTU, you are either choosing one that is too low, or one that is too high for your room.
Issues of BTU that is too low: If you choose an aircon with a BTU that is too low, it will result in longer cooling times, a poor cooling capacity, and also a higher electricity bill. Because the air conditioning unit is underpowered, what will happen is that it will have to operate for a longer period just so that it can bring the room to the best temperature. And because it is operating longer, that then impacts the electricity bill and costs you more in energy in the long run.
Issues of BTU that is too high: One would think that perhaps choosing a larger BTU would then mean the opposite, and cool a room much faster, which would be good. However, this is a common misconception and there are actually downsides with choosing an oversized aircon. The issue here is that you aircon is supposed to both lower the temperature and also remove moisture from the air. This keeps you cool and comfortable. However, with an aircon that is too large, what happens is that while the cooling happens very rapidly, the moisture extraction does not keep up. This will mean that while it is cooler, the moisture is still in the air and starts to condense. This can make you feel humid and sticky. Furthermore, because the aircon is too powerful, it will have to stop its cooling cycle very frequently, and start again. This extra cycles creates extra load on the compressor and this causes your aircon lifespan to be reduced.
So given the above, it is absolutely critical that you choose just the right BTU for your air conditioners — especially for a tropical country like Singapore.
Now we’ve shown you the math needed to calculate the right BTU, and also the importance of choosing the right and best number. Now to make your life even easier, we’ve taken the most common room sizes and made a table for easy reference.
Not every room and every house are created equal – some are on different floors, get different amount of sun exposure etc and all of this also has some impact on the optimal BTU. So in this section we will outline the other factors that you should consider when choosing BTU, and how to adjust your optimal BTU accordingly.
1. Floor of House
Typically, the top floor of the house will receive more heat and its share of sunlight. This is logical because the top floor directly borders the roof, which absorbs and transmits heat from direct sunlight. Meanwhile, the floors below would be insulated from that direct sunlight by the top floor. As such, if your room is on the top floor, we would recommend that you adjust the BTU upwards by 10%.
2. Degree of Shade
Again, the rooms in a house sometimes face the sun directly or are in the shade most of the time. This again will affect the amount of humidity that the room accumulates and thus has to be removed. Our recommendation is that if that room faces the sun and has its own share of considerable heat, especially during the hotter times of the day, increase the cooling BTU required by 10%. Conversely, if the room mostly faces the shade or does not get its share of direct sunlight, you can reduce the BTU estimate by 10%.
3. Number of Persons in the Room
As people, we all generate body heat. This is why it is so hot in a packed concert. If you typically have a lot of people in a room, e.g. a living room, bedroom, classroom or conference room, you will have to factor that into your BTU calculations. In general, the calculations that we have assume 2 people in the room. If you have more than 2 people, the rule of thumb here is to add 600 BTU per extra person you expect the room to handle.
4. Heat Generating Home Appliances
Our home appliances also generate a lot of warm energy. Appliances with high electrical consumptions like the refrigerator generate this the most. If you are calculating the BTU for your kitchen which will have a lot of heat-generating items like the stove, the fridge, ovens, etc. then we would want to take into account that is heat which the air conditioner has to remove. So in these cases, for rooms like the kitchen, we recommend adding 4000 BTU to the number derived above.
5. Ability to Close Off Cooling Space
Sometimes, your bedrooms may be connected to another room, and there may not be a door between the rooms. In these cases, you would want to add the size of both rooms together to calculate the BTU. This is because the air will circulate between the two rooms, and the real load on your air conditioner is actually the sum of the volumes.
We hope this guide explains what BTU is, why it matters in choosing air conditioners, and helps you choose the best air conditioner for your needs!