Load Calculations, Sizing, and Energy Code Requirements
This domain tests load calculations, equipment selection, airflow, and New Jersey energy-code requirements. The exam expects Manual J, S, and D logic rather than square-foot rules.
Loads and sizing
Manual J calculates room-by-room sensible and latent loads using design conditions, envelope, infiltration, internal gains, and duct losses. Manual S selects equipment using actual capacity at design conditions, not nominal tonnage. Manual D sizes ducts. In New Jersey's humid summer, latent capacity matters; oversizing reduces runtime and dehumidification.
Energy code
The Uniform Construction Code adopts the IECC with state amendments. Requirements include envelope insulation, duct sealing and insulation, equipment efficiency (SEER2, HSPF2, AFUE), and ventilation. Verify the edition in force before submitting plans.
Worked example
A room has a Manual J sensible load of 24,000 Btu/h with a 20°F design temperature difference. Required airflow = 24,000 ÷ (1.08 × 20) = 1,111 cfm. At 400 cfm/ton, that is about 2.8 tons; select equipment whose actual capacity covers both sensible and latent load, then set airflow per the manufacturer. Do not size from 500 ft²/ton.
What costs marks
- Using square footage or “one ton per 500 ft².”
- Ignoring latent load and duct gain.
- Selecting nominal tonnage without checking capacity tables.
- Forgetting duct sealing in unconditioned spaces.
- Using outdated efficiency metrics such as SEER instead of SEER2.