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Yes,,problem has been there for three years..whole place smelled like poo for three years until a gc removed the rubber plugs from outside vent (way a way to go Mr. plumber ) ..now commode smell vent up pipe. Now about this kitchen exhaust fan....I looked at all the data and curves.. don't have a flow hood..belts are all good. could balance using transference from The other units but it makes the Ducks wet when I do that...

the real question is if this is a recent development, were things going on ok before they called you in the past, then I would agree check the power ventilator operation.

Can u slow it down other than loosening the belt ?

I would also check any mixing boxes or economizers. They might all be at 100 recirc, and the system requires more outside air. If they pulling in outside air, you may need to look into speeding up the units to bring in more outside air. One other solution is to slow down the exhaust on the kitchen hoods. They have a min CFM usually listed on the hood. I would double check what the hood is pulling VS the CFM it should be. Hope that helps.

I agree with RACMT. I see make up air belts torn up all of the time. Or the motor burns up....or the bearings break....

For commercial kitchens they usually want them in a slight negative pressure, just below the neutral pressure plane, this is so smells and smoke doesn't make it into the dining room. But you might have a make up air unit and the belt might be broken. You have to go on the roof to confirm, something so small can cause such a noticeable problem like door slamming shut. Also refer to local codes.

Did you go on the roof? MU/air might be discharged into the conditioned space and maybe it is not working. Check your local codes as far as conditioning the air. Where I'm at, if the air is dumping into the hood it does not need conditioning. Anywhere else it does. You will need to do or have someone do an air balance to find out what needs to be done.

Question about a kitchen hood

I went to a restaurant yesterday because they complained the temperature in the restaurant and I noticed the restaurant is in a huge negative static pressure, the doors will not close from so much air trying to get into the restaurant (The doors close from inside out if you're wondering). I noticed the kitchen hood does not have a makeup air around the "lip" of the hood like I have seen at other restaurants. My question is how would I know how much CFM needs to be entered into the restaurant and what would be the best application in this situation.

It will probably have to go on the roof but do I need a preheat system? Or is an outside air only unit OK to use? will this make the restaurant to cold in the winter?

Any answer provided would be a big help. Thank You ALL