Ventilation equipment operating in the home can create which effect?

• A. Ventilation effect, generating pressure differences that drive air flow.
• B. Mechanical effect only when combustion devices are present.
• C. No effect on indoor air pressure.
• D. Always equalizes indoor and outdoor pressure.

Answer: (A)

Ventilation devices work by moving air with a fan, which creates a difference in air pressure between the indoors and outdoors. Air always flows from higher pressure to lower pressure, so when a fan exhausts air from the house, the inside becomes slightly negative and outdoor air is drawn in to balance it. Conversely, a supply fan pushes air in, making the indoors slightly more pressurized and causing air to escape through leaks or exhaust paths. This pressure difference is what drives the continuous air exchange the system provides. It’s not true that there’s no effect on indoor pressure, nor that pressure is always perfectly equalized, and it doesn’t require combustion devices to have an effect.