RADEX non-LTE modeling of the relation between the gas kinetic temperature and the para-H₂CO 3₂₁–2₂₀/3₀₃–2₀₂ integrated intensity ratio (solid line), assuming n(H₂) = 10⁵ cm^-3, N(para-H₂CO) = 2.1 × 10¹² cm^-2, and a line width of 6 km s^-1. Blue points are the results derived from the measured para-H₂CO 3₂₁–2₂₀/3₀₃–2₀₂ and para-H₂CO 3₀₃–2₀₂/C¹⁸O 2–1 ratios. For N159S, 3σ upper limits for the line ratio and the kinetic temperature have been taken.