Exhaust air ventilation
In an exhaust air ventilation system, a fan runs continuously and this generates a slight vacuum in the house.
Fresh air is drawn in through registers and leakages in the building. Polluted room air is extracted by means of an exhaust air fan, located in the attic in the above illustration. Illustration: Bo Reinerdahl
Supply air is admitted through outdoor air registers that may be fitted in window frames or in walls. There are self-regulating outdoor air registers that limit the air flow when the outdoor air temperature is very low. To enable the air to circulate inside the house, it must be able to flow through gaps at the bottom or top of doors.
Some maintenance is needed to ensure good performance of the ventilation system. Make sure that the ducts, fans and registers are clean, so that the flow of air will not be impaired. There is otherwise risk of the air circulation being inadequate and the fan efficiency will drop. Change the fan filter at regular intervals.
It is possible to connect a heat pump to the exhaust air fan to enable heat to be recovered from the ventilation air.