Providing the right temperature in the living space has been one of the needs of human beings today, and therefore the use of different types of cooling and heating systems in buildings has become common. By replacing the energy from fossil fuels with heating and cooling systems with renewable energy, there will be significant effects on optimizing energy consumption, reducing the growing trend of global temperatures, reducing air pollution, and reducing fossil fuel consumption. In this paper, the technical-environmental performance of solar heating systems in Iran and the effect of buffer tank type on their performance using Valentin T*SOL software in 3 different configurations and in climatic conditions of 3 cities of Tabriz, Tehran and Shiraz have been studied. Is. The studies showed that in the first arrangement (using a hot water tank) in Shiraz had the greatest savings in natural gas consumption and the greatest reduction in CO2 emissions. In the second arrangement (using two hot water tanks) in Tabriz, the highest savings in natural gas consumption have the greatest reduction in CO2 emissions and the amount of energy produced, and in the third arrangement (thermosiphon system) in Shiraz with the greatest savings in natural gas consumption and Reduced CO2 emissions have been associated. The results of the present work show the need to study different systems for stations located in different climates to find the most suitable system for each station. Manuscript profile