A comparison of passive stack ventilation and mechanical extract fans in reducing condensation problems in homes.

A study comparing the effectiveness (as reported by occupants) of passive stack ventilation (PSY) and mechanical extract fans (MEFs) was carried out during the winter of 1996. This involved a face-to-face survey of 437 homes in England. More than 50% of the homes in the study had MEFs, 14% had PSV and 8% had humidistat-controlled MEFs (HMEFs). About 25% of the homes had either a kitchen or a bathroom with no ventilation device and 16% had no ventilation device in the home. Four measures of condensation problems were analysed: condensation overall in the home, in the kitchen and in the bathroom, and a combined index of condensation and mould. For the measures analysed, the reported effectiveness of PSV and MEFs was not significantly different. The effectiveness of both, however, was reported to be better than HMEFs. This report concludes that allowing the use of PSY for dwellings is supported by these results. HMEFs may save energy, but are reported by occupants to be less effective. However, this may be due to problems with their acceptance and use by occupants, rather than any technical failing.