This study aims to provide a detailed understanding of indoor environment. The study has been undertaken as part of the Energy Innovation for Deprived Communities (EIDC) project, which aims to deliver a new approach to energy efficiency and renewable energy projects within a minimum of 10 of the most deprived communities across 6 Local Authorities within Yorkshire and the Humber, UK. It is important for the success of the EIDC project that detailed monitoring and post occupancy evaluation is performed on a sample of houses before rolling out wider refurbishment. The data were collected from the indoor monitoring equipment for two housed and statistically analysed to investigate the indoor thermal condition and air quality. Temperature and relative humidity levels within an indoor environment will vary with the time of year and physical indoor environment. However, increased temperature within a confined space such as an indoor environment can create a more suitable environment for the growth of unwanted bacteria and fungi. In general, it would be reasonable to maintain a temperature of around 23°C to 25°C within an house. Also If levels of humidity become too dry, below 40% this can have adverse effects, some people susceptible to sore throats due to the dryness of the air. The optimum level of humidity should be between 40-70%. Air temperature (°C), relative humidity (RH%), and carbon dioxide (CO2) were monitored and the results were compared to accepted standard guidelines. The results showed that the indoor thermal environment conditions in the two naturally ventilated homes had a mean air temperature and relative humidity of 20.5 °C and 47% respectively in autumn time. The mean CO2 levels were in the range 520 to 1400 ppm and followed a pattern that rising during morning and evening in response to human indoor activity. Detailed analysis of CO2 at four periods during the day showed that afternoon times contained lower values of CO2 compared with morning, and evening.