Infiltration is how air gets into our houses and buildings, even when we don't want it to. It happens when the outside air is able to sneak in through tiny cracks or gaps in our doors, windows, floors, and walls.
Like when you blow bubbles in the bath and the water spreads out, air moves the same way. When the air outside is warmer (or cooler) than the air inside, it tries to move inside to balance out the temperature. Even though we want our homes to be comfortable, we don't want to spend extra money to heat or cool extra air that comes in through these gaps.
That's why HVAC (heating, ventilation, and air conditioning) systems are designed to help control infiltration. Their job is to manage the air inside our buildings and control the temperature, humidity, and air quality. They use things like filters, ducts, and vents to bring in fresh air when needed and push out stale air to keep the air inside clean and healthy.
So, infiltration is like a sneaky visitor that tries to get into our homes, but HVAC systems are like secret agents that protect us and keep us comfortable by managing the air inside.