Three different approaches to estimate the vapor pressure by thermogravimetric analyses (TGA) of commercial paraffins-based phase change materials (PCMs) have been compared. The known Langmuir vaporization relation and two additional models based on the mass transfer by molecular diffusion at isothermal and non-isothermal conditions, using the Fuller equation for estimating binary diffusion coefficients in the gas phase, were developed. The Antoine equation was used to express vapor pressure as function of temperature and the unknown constants were obtained by non-linear regression. n-Hexadecane and n-decane were used as reference compounds to estimate the deviation between experimental and predicted values. The non-isothermal model exhibited the highest accuracy for obtaining the vapor pressure and allowed to obtain boiling points and heat of vaporizations very close to those reported for the reference compounds.