This paper presents an assessment of how to minimise excessive energy consumption in a case study school classroom while maintaining optimal indoor air quality. Using mixed method research with qualitative interview data supporting quantitative key data measurements, essential primary data was extracted from temperature and carbon dioxide monitoring equipment in the classroom. This was then used, along with other ancillary data, to develop an IES computer model of the classroom as a “base case” reflecting existing energy consumption, temperatures and CO2 levels. Eight different interventions were then developed and modelled which reflected improved energy supply and a variety of ventilation strategies. The results show that adequate control and design of energy supply systems is critical to minimising excessive energy consumption, and that adequate internal air quality is achievable through a variety of low cost strategies.