Power of Extractor Fan

[mhadley]

I am installing an externally ventilated chimney style extractor fan in the kitchen and need to know how powerful of a fan I will need to install. Here are some of the facts: The kitchen is approx 20sqm. After venting into the ceiling the duct work has a 45 degree bend, then runs horizontially along the celing for approx 4 meters, then another 45 degree bend to vent vertically to the outside through a chimney. The chimney is 3 meters long. I assume the duct is approx 12-15cm in width. So given these factors would a extractor fan that can ventilate 700-800cubic meters per hour be strong enough to push air out of the chimney? I would appeciate any comments on how to caculate the proper matching of extractor fan to ventilation system. Thanks, Matt

 

[bernardgreen]

The volume moved will depend on the pressure created by the fan against the resistance of the duct work to air moving through it. The technical data on the duct work will provide the resistance per component of ducting. Add them up and then look at the graphs of flow / pressure graphs in the data of the available fans.

It is important to remember that there must be an easy route for air INTO the kitchen to replace the air extracted. If there isn't then the resistance to air entering the kitchen has to be added to the equation.

Discharging warm moist air into a chimney has problems. If the warm moist air mixes with cold air in the chimney there will be condensation in the chimney which will create damp and related problems ( mold ) in the base of the chimney.

 

[electronicsuk]

With 45 degree bends and using solid ducting rather than corrugated, you shouldn't have a major problem in terms of pressure buildup in the duct.