Exhaust Fan Negative Pressure

How exactly does air pressure get out of balance.

Exhaust fan negative pressure.

The air blowing into the house would increase air pressure and force the smoke out of the rooms. Let s put some numbers to that idea. The negative pressure created by the exhaust fans is really something we have to worry about. The article will analyze negative pressure ventilation systems in maintaining air quality house temperature and air movement.

Warm air in your building rises to the upper floors and can result in negative air pressure in the. Conversely if the smoke was localized then we would place the fan about 6 from the door on the inside of the house facing out thus creating a negative pressure in the house. Divide your answer by the system airflow in cubic feet per minute. Static pressure in fan systems is typically less than 2 sp or 0 072 psi.

Like combustion appliances exhaust fans can remove too much air and cause negative air pressure. Positive pressure is simply more effective than negative pressure for aggressive coordinated attack. When should negative pressure ventilation be used. Most homes have at least one negative pressure room.

With two intake fans and three exhaust fans this setup creates negative air pressure. When a bathroom door is closed if the bathroom has a quality working fan unpleasant odors as well as moisture and humidity are vented out through the fan because the forced air ventilation creates a negative pressure room. The exhaust fan drawing below illustrates how static pressures are measured in ductwork with a manometer. My house currently has a blower door test result of 5 200 cubic feet per minute at 50 pascals of pressure difference 5 200 cfm50.

A pressure differential between the duct and the atmosphere will cause the water level in the manometer legs to rest at different levels. The more airtight the house the bigger that negative pressure will be. Negative pressure isolation rooms. Ventry fans are not exhaust fans.

This is the exhaust fan s static pressure. Both approaches have their advantages. It the fan moves 200 cfm then 1 970 200 9 85. Exhaust fans in your bathrooms and kitchen of course will induce some negative pressure.

Negative air pressure should create a slightly cooler environment at least in theory as the fans are working harder to expel hot air.