Describes a simple method of controlled ventilation comprising an extract system and air inlets. The extract system is effectively a flue connecting to vents in the kitchen and bathroom and relying on thermal differences and the wind to create air flow, air enters the house via slot vents over windows. Theproposed system has been installed in a timber framed house. Air has been extracted through the system up to the equivalent of 0.3 ac/h for the house volume, but this is less than expected.< The house needs to be tightly constructed, the extract tubes need to have very low air resistance and care is needed in siting the inlets for efficient operation. The effect of wind has not been measured, but a device may be necessary to prevent over-extraction. Modifications to the system are proposedfor future work.