Simulating natural convection in a large volume requires significant computational efforts using powerful servers. While scientific research requires high accuracy, applied engineering solution requirements for accuracy can be lowered. The aim of this article is to analyse modern methods of modelling natural convection in a large volume for solving applied problems and choosing the best method when resources are limited. In this paper we reviewed various approaches and the experience of other authors in solving similar problems and proposed a method for calculating the simulation model of the RGSn-100 storage tank with HB-6-1-3000 in-line electric heating in the ANSYS 2021 R1 Fluent. The proposed method reduces the computational effort required by a factor of ten thousand while maintaining the engineering accuracy of calculations.