Ref MVHR intakes.....what happens if:   The fresh air intake is downwind of say muck spreading, a neighbour (or you) emptying their cess pool or a bonfire / adjacent house fire Presumably things get very stinky/smokey pretty quickly. During the day I guess you shut the system down. I appreciate there are filters but down to what level? But at night? Could it get to the point that smokes in the house would go off?