In winter, with an exhaust air extractor, along with the cooking vapours warm heating air is also channelled outside the building. The result: valuable energy is lost. In passive homes or particularly airtight low-energy homes, this can negatively affect the home’s energy balance. For this reason, building experts recommend installing recirculating air systems rather than kitchen exhaust air systems with conventional extractor hoods in highly insulated new builds. In many new builds kitchen exhaust air systems are even prohibited. Contrary to conventional extractor hoods BORA systems work with a relatively low displacement volume, whereby from the outset very little warm air from the room escapes to the outside, however, in airtight buildings recirculating air is often the best option as such buildings generally have controlled ventilation systems. This automatic ventilation allowing the air to enter and exit the room ensures that moisture is safely carried away and, together with a recirculating air extractor, the air in the kitchen remains fresh. In old buildings, on the contrary, kitchen exhaust air is normally recommended. This is because there are often large temperature differences in old buildings, which encourage the formation of condensation. With a kitchen exhaust air system, the moisture in the air is quickly removed to the outside.