Indoor Air Quality A study was carried out to compare CO2 levels in bedrooms by MosArt, a leading Irish environmental design practice. They compared levels in a conventional house with those in an air-tight house which had mechanical ventilation with heat recovery installed. The results for a 4 day period are shown in the attached graph. CO2 concentrations in excess of 1000 ppm suggest inadequate ventilation. Problems such as lack of concentration, headaches and general drowsiness start to appear at high CO2 levels. Optimal conditions minimising health risks to humans occur when the Relative Humidity (RH) at normal room temperatures is between 40% and 60%. Bacteria, moulds and viruses all thrive in clammy moist environments. These can cause coughing, lung irritation and general discomfort. A comfortable and healthy indoor environment in terms of temperature and relative humidity is represented below A paper published in 1986 in the journal, Environmental Health Perspectives by Arundel Anthony V et al, (Indirect Health Effects of Relative Humidity in Indoor Environments), showed that many adverse health effects increase severity above 60% RH and/or below 40% RH. Among the health effects listed were levels of bacteria, viruses, mites, fungi, respiratory infections, allergic rhinitis and asthma, chemical interactions and ozone production. Optimum relative humidity range for minimising adverse health risks. Maximum advantage should be taken of new technologies to improve IAQ. Ventilation plays a crucial role in relation to indoor pollution levels. A ProAir heat recovery ventilation system will reduce the relative humidity of the indoor air to c50%. The incoming fresh air is filtered to remove any large particulate matter. At the same time sufficient fresh air is being supplied and energy requirement is reduced.