Exhaust Fan Negative Pressure

The exhaust fan drawing below illustrates how static pressures are measured in ductwork with a manometer.

Exhaust fan negative pressure.

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. Ventry fans are designed for positive pressure ventilation ppv and attack ppa. Exhaust fans or smoke ejection fans use negative pressure to remove smoke from a structure during firefighting efforts. The more airtight the house the bigger that negative pressure will be.

Like combustion appliances exhaust fans can remove too much air and cause negative air pressure. 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. When retrofitting a standard patient room for use as a negative pressure isolation room it is not often practical to exhaust the air directly outdoors as required. Let s put some numbers to that idea.

A pressure differential between the duct and the atmosphere will cause the water level in the manometer legs to rest at different levels. 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. Static pressure in fan systems is typically less than 2 sp or 0 072 psi. Negative air pressure should create a slightly cooler environment at least in theory as the fans are working harder to expel hot air.

Exhaust fans in your bathrooms and kitchen of course will induce some negative pressure. How exactly does air pressure get out of balance. This is the exhaust fan s static pressure. Warm air in your building rises to the upper floors and can result in negative air pressure in the.

The negative pressure created by the exhaust fans is really something we have to worry about. Both approaches have their advantages. The air blowing into the house would increase air pressure and force the smoke out of the rooms. The article will analyze negative pressure ventilation systems in maintaining air quality house temperature and air movement.

It the fan moves 200 cfm then 1 970 200 9 85. Most homes have at least one negative pressure room. Positive pressure is simply more effective than negative pressure for aggressive coordinated attack. Negative pressure isolation rooms.

With two intake fans and three exhaust fans this setup creates negative air pressure.