The main aim of any kind of ventilation systems is to ensure optimal comfort conditions of indoor air quality for inhabitants independently of outdoor air parameters. Until the end of 90-ties all dwelling buildings in Latvia were equipped with mandatory natural ventilation systems with stack effect. Nowadays in many cases there is only exhaust mechanical ventilation in dwellings but air tight windows prevent natural air intake. The operation of existing ventilation systems is inefficient and result in bad IAQ. Installation of regular mechanical “inflow - outflow” ventilation systems in dwelling buildings was limited by such factors as high noise level during operation time, limited buildings’ area and high construction expenses. In order to improve the situation in existing multi –flats buildings new technical decisions are being introduced. One of such decisions is use of hybrid ventilation. The implementation of principles of hybrid ventilation systems in Latvia poses some difficulties due to climatic conditions. In general Latvian climate can be described by moderate temperatures with all year round high relative humidity. In order to ensure optimal comfort parameters of indoor air it is necessary to use not only air heating devices but also air humidifiers. The paper deals with Latvian average climate parameters on the basis of statistical data for 10 year time period. As the result optimal working regimes of ventilation systems are found. The paper studies the principles of the ventilation systems’ automatic control in any climatic conditions. It was found out that in Latvian typical apartment buildings annual energy consumptions for traditional ventilation and for heating are approximately identical. Providing comfortable relative humidity of indoor air annual heat consumption for ventilation considerably increases.