# Fan Interlock!



## erics37 (May 7, 2009)

Mcsparkin said:


> Worked for a company for years that used a current sensing donut and relay to turn the air intake on when the exhaust fans were running. I was wondering how others accomplished this? I would like to be accustomed to other ways of achieving intake/exhaust interlock to avoid pilot light getting "sucked" off *snicker*


"Fan status" current switches and "Fan start/stop" relays are typical with HVAC control systems. There was probably a programmed controller module somewhere with the exhaust fan and intake inputs and outputs wired to it. Or it could have been old school and had a relay board.


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## walkerj (May 13, 2007)

Relay in a box.


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## Wirenuting (Sep 12, 2010)

Aux contact on the starter. 
I don't like fans sucking when they shouldn't be. 

Besides, in a few of our larger kitchens, the make up dampers opened before the exhaust started. This prevented unwanted back sucking. 
If a supply fan fed the space, that aux contact began the exhaust fan sequence. 
Dampers before the fan starts.


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