New Zealand has a temperate maritime climate. Despite mild winters compared to nations with continental climates, New Zealand houses have been reported to often be at temperatures below internationally recommended levels. Sources of additional heating are therefore of interest to many New Zealand home occupants. Roof space solar gains have been identified as one possible source of heating. This paper investigates the energy gains available in New Zealand homes from ventilation systems drawing air from the roof cavity. Three New Zealand houses were monitored and a computer-based thermal building simulation developed to quantify the heating and cooling energy that might be transferred by home ventilation systems. The computer model simulating the temperature in the roof space and occupied spaces was constructed using MATLAB, and used publicly available weather station data as the inputs. A good match between measured and modelled results was obtained. Small heating and cooling benefits are possible at certain times from pumping roof space air into the living areas of some New Zealand houses. The magnitude of these benefits, however, is not significant compared with the space heating required to maintain reasonable indoor temperatures over the New Zealand winter. (C) 2011 Elsevier B.V. All rights reserved.