The paper presents a linear and non-linear study of convection in a viscoelastic dielectric liquids. The upper convected Jeffrey model, also known as Oldroyd-B model is used to represent the viscoelasticity. A modified method of the Venezian type is used to obtain a correction to the eigenvalue. The Khayat-Lorenz model is derived for the dielectric liquid with the aid of minimal mode double Fourier series. The classical Lorenz model is obtained as a limiting case of the present study. The effect of different parameters on heat transfer is presented. A comparison of heat transfer in different viscoelastic liquids is also discussed.