CSLB C-20 HVAC ContractorVentilation and Air DistributionEasy
A technician is commissioning a new 3-ton residential split-system air conditioner. Using the standard industry rule of thumb for cooling airflow, what target airflow should the system deliver?
- A1,200 CFM
- B1,500 CFM
- C900 CFM
- D2,000 CFM
Show answer & explanationAnswer & explanation
Correct answer: A. 1,200 CFM
The standard rule of thumb for residential cooling design is approximately 400 CFM per ton of capacity. For a 3-ton system: 3 tons × 400 CFM/ton = 1,200 CFM.
Why the other options are wrong
- B. This would be 500 CFM/ton, higher than typical residential design airflow.
- C. This is only 300 CFM/ton, below the typical design target.
- D. This value is far above the standard design ratio and would indicate an oversized duct or undersized coil mismatch.
CFM per Ton Rule of Thumb
Residential cooling systems are typically designed to deliver about 400 CFM of airflow per ton of cooling capacity to achieve proper sensible/latent split and coil performance.
- 1 ton = 12,000 BTU/hr
- Standard design airflow ≈ 400 CFM/ton
- Humid climates may target 350 CFM/ton for better dehumidification
Memory trick: '400 for cooling, keep it flowing.'