The building sector accounts for as much as 40% of total energy consumption. Currently, in Poland, most energy is used for heating. For this reason, engineers focus on reducing heating demand, for example by increasing thermal insulation of external walls of the designed buildings. The heat exchange with an outdoor environment in such buildings is limited and might significantly reduce the thermal comfort in a summer period. As a consequence, it may contribute to increased morbidity. The problem can increase with global warming. The aim of the paper is the analysis of heating and cooling demand and human thermal comfort in a single-family house for different climate data and for various types of thermal insulation of building external partitions. In the study two ways of cooling building were taken into account: 1) by using air conditioners and 2) by using outdoor air, where the airflow depends on the angle of a window opening. Two cases were considered for weather files, in the first case for typical weather files from 30-years-period (standard weather data) and in the second for data from the 2018. EnergyPlus software was used to carry out the simulation. The multi-zone model of an existing single-family house was prepared. The model was validated and calibrated based on the indoor temperature measurement. The results of the calculation have shown that due to the climate change, external environment is getting warmer resulting in a decrease in annual heating demand and increase in annual cooling demand, especially in passive buildings. The use of the ventilative cooling instead of the mechanical cooling is a good solution for single-family house. The number of discomfort hours is small compared to all the hours while people are staying in the rooms. This solution causes lower electricity consumption, which in the case of Poland comes mainly from coal-fired power plants.