My shop has 2 ceiling registers that blow air whenever the furnace or A/C is on, so if I am making any dust, even with the DC on and the ambient cleaner going, some dust will be circulated to the rest of the house. That is one downside to a shared HVAC system in a home. Without those registers open it can get real chilly in the shop. Small price to pay. The amount of time that there might be dust in the shop air and the furnace is running is quite small.