Considerable scientific effort and financial resources are involved in conserving historic buildings and creating appropriate indoor climate conditions and thermal comfort for users, visitors, exhibited objects, and the building itself. In Slovenia, the idea of establishing a central monitoring system for heritage buildings was the first step realised as part of participation in the EUREKA Project 1383 PREVENT. In order to improve the indoor conditions in historic buildings and to realise preventive restoration strategy, an international co-operation was established through the PREVENT project based on the permanent monitoring of indoor climate in heritage buildings. The idea of using the “wall heating” method for energy-efficient improvement of microclimatic control in historic buildings was investigated as an additional step. In this paper, climate monitoring in different types of heritage buildings (heated and unheated) in Slovenia is described and the effects of wall tempering on indoor climate are presented in more detail, based on computer simulations and monitoring the performance of demo-installations. Further ideas for research on improving indoor climate and consequently integrated preventive conservation are also described.