A study is made of the steady state heat balance of the O+, H+, and electron gases in the topside of the nocturnal equatorial ionosphere. The method used is that developed previously by Bailey and others; input plasma concentrations and drift velocities are taken from work by Moffett and Hanson. In the present study, additional terms in the plasma heat flow vectors, as suggested by St.-Maurice and Schunk, are included. The additional term that depends on relative flow of O+ and H+ gives rise to diffusion-thermal effects in the O+ and H+ gases. On the other hand, with a zero-current condition relating the electron, O+, and H+ field-aligned flows, the electron heat flow vector reduces to the usual thermal conduction form. It is found that for the conditions considered, on the field line with equatorial crossing point at about 800 km at 2200 LT, the H+ temperature is raised by about 50 K and the O+ temperature is raised by about 30 K over the equator in comparison with results obtained when the terms suggested by St.-Maurice and Schunk are omitted. In the winter hemisphere the H+ temperature may be lowered by about 20 K, and the O+ temperature by about 10 K. It is suggested that diffusion-thermal effects will become more important with increasing altitude in the equatorial topside ionosphere at night.