NATE Core cheat sheet
NATE Core · Keep the key ideas within reach.
Core HVACR Fundamentals
Sensible heat formula: Qs = 1.08 × CFM × ΔT (BTU/h, sea level); latent heat: QL = 0.68 × CFM × ΔW (grains/lb).
Total heat (enthalpy) formula: Qt = 4.5 × CFM × Δh, where h is enthalpy in BTU/lb dry air.
Pressure conversions: 1 psi = 2.31 ft of water; 1 in. w.c. = 0.0361 psi; 1 atmosphere = 14.696 psi = 29.92 inHg.
Temperature conversions: °F = (°C × 1.8) + 32; °C = (°F − 32) / 1.8; absolute zero = −459.67°F = −273.15°C.
Ohm's law: E = I × R; power: P = E × I (watts); for three-phase: P = E × I × 1.732 × power factor.
Superheat = actual suction line temp − saturation temp at suction pressure; subcooling = saturation temp at liquid pressure − actual liquid line temp.
Refrigerant glide: difference between dew point and bubble point at a given pressure; zeotropic blends require average or midpoint for charging.
Air properties: standard air density = 0.075 lb/ft³ at 70°F and sea level; specific heat of air ≈ 0.24 BTU/lb·°F.