1 Introduction  
2 Methodology  
3 Recommender systems for energy efficiency in buildings  
3.1 The objectives of energy efficiency recommender systems  
3.2 Methodologies and algorithms for energy efficiency recommendations  
3.3 Computing platforms  
3.4 Evaluation metrics  
3.5 Incentive measures  
4 Critical analysis and discussion  
4.1 Limitations and difficulties  
4.2 Commercialization of developed solutions  
5 Current challenges and future orientations  
5.1 Current challenges  
5.2 Future orientations  
6 Conclusions