Is your AC really 3-tons?

Understanding how an air conditioner functions, its energy rating, cooling capacity and other factors is slightly complicated to understand; especially as there as so many values and numericals involved.

What does it mean when you install an air conditioner that is 3 tons? Is that the weight of the AC? Is that the cooling capacity? Why is it weighed in tons?

One may have many questions related to air conditioner weight or tonnage. Let’s try to see what this value really means.

1. What is AC tonnage?

Air conditioning and heating capacities are generally measured in British Thermal Units (Btu) per hour. This refers to the amount of heat required to increase the temperature of a pound of water by one degree.

Air conditioner cooling capacity is described in ‘tons.’ One ton means the rate of heat transfer needed to freeze one ton of water in 24 hours. This is equivalent to 12,000 Btu/hr.

So, a 3-ton AC for instance, does not actually weigh 3 tons. It means that it has a nominal capacity of 36,000 Btu/hr.

2. How does AC capacity affect cooling?

Because of this system, home owners often feel that a bigger AC is better as it has higher cooling capacity. But this is not necessarily beneficial for your house. An over-sized conditioner will face short cycling (constant shutting down and restarting of the compressor). This results in too much pressure on the system, early wear and tear, and the need for recurrent repairs. It also prevents the air conditioner from dehumidifying indoor air. As a result, your Bay Area house may be cool but will still feel clammy. If you decrease the AC temperature further to combat this problem, it will raise your monthly energy bills.

3. Nominal capacity and actual capacity

Nominal capacity refers to the capacity of the air conditioner that manufacturers claim their product has, when they are selling it. This is also known as nameplate capacity. This is the number that you will find on your product or one that a sales manager will use while telling you the AC capacity and features. But it does not mean that 3 ton, for instance is the actual cooling capacity of the air conditioner.

Cooling a house depends on many factors, not just the HVAC system in itself. As other factors are variable, the actual capacity of an AC is slightly lesser than the mentioned nominal capacity.

4. Operating conditions

Operating conditions for ACs are quite different once you install it in your house. Ambient temperature and humidity play a big role in how well your AC can cool or remove moisture from air. Due to actual operating conditions, ACs are usually able to cool less than their capacity and hence, you may have to purchase a unit that is 3.5 ton instead of 3, for example; for comfortable cooling.

5. Other reasons for capacity variation

Air conditioner cooling capacity may also be low due to other factors like bad ductwork, dirty coils and poor airflow. Resolve these issues instead of oversizing your AC.