What is CFM Per Ton?
CFM per ton is a critical measurement in HVAC systems that relates airflow to cooling capacity. CFM stands for Cubic Feet per Minute, measuring how much air moves through your system. Tonnage refers to cooling capacity, where one ton equals 12,000 BTU per hour of cooling.
The relationship between these two values tells you whether your HVAC system is properly balanced. An imbalanced system wastes energy, provides poor comfort, and can damage equipment over time.
The CFM Per Ton Formula
The calculation is straightforward division:
$$\text{CFM Per Ton} = \frac{\text{Total Airflow (CFM)}}{\text{Cooling Capacity (tons)}}$$
Where:
- Total Airflow is the volume of air moving through the system in cubic feet per minute
- Cooling Capacity is the system's cooling power in tons (1 ton = 12,000 BTU/hr)
- CFM Per Ton is the resulting airflow rate per unit of cooling capacity
Industry Standards
The HVAC industry uses 400 CFM per ton as the standard baseline. Here is what different values indicate:
- 350-400 CFM/ton: Lower range, better for humid climates where moisture removal is priority
- 400 CFM/ton: Standard baseline for most residential and commercial applications
- 400-450 CFM/ton: Higher range, suitable for dry climates where sensible cooling is priority
Calculation Example
Consider an air conditioning system with 1,600 CFM total airflow and 4 tons of cooling capacity:
$$\text{CFM Per Ton} = \frac{1{,}600}{4} = 400$$
This system delivers exactly 400 CFM per ton, right at the industry standard. The system is properly balanced for typical residential applications.
Another Example
A commercial system delivers 2,800 CFM with 7 tons of cooling:
$$\text{CFM Per Ton} = \frac{2{,}800}{7} = 400$$
Again, this yields 400 CFM per ton, indicating proper system balance.
Example with Low CFM Per Ton
An older system moves 1,200 CFM with 4 tons of capacity:
$$\text{CFM Per Ton} = \frac{1{,}200}{4} = 300$$
At 300 CFM per ton, this system has restricted airflow. The evaporator coil may ice up, efficiency drops, and the compressor works harder than necessary. This system needs airflow improvements such as duct cleaning, filter replacement, or blower adjustment.
Why CFM Per Ton Matters
Proper CFM per ton ensures:
- Efficient heat transfer across the evaporator coil
- Proper humidity control by allowing adequate contact time with cold coil
- Equipment longevity by preventing coil icing and compressor strain
- Consistent comfort throughout conditioned spaces
- Energy efficiency by optimizing system performance
Key Takeaways
- The standard CFM per ton is 400 for most HVAC applications
- Acceptable range is typically 350-450 CFM per ton
- Low values indicate restricted airflow that needs correction
- High values indicate excessive airflow that reduces dehumidification
- Regular system maintenance helps maintain proper CFM per ton